GAO-11-71 Climate Engineering: Technical Status, Future Directions, and Potential Responses

Climate engineering

Center for Science, Technology, and Engineering

United States Government Accountability Oce

GAO

July 2011

GAO-11-71

Technical status, future directions, and

potential responses

TECHNOLOGY ASSESSMENT

2 What are potential future directions

for research on climate engineering

technologies, 2010 through 2030, and

possible consequences?

1 What is the current state of

climate engineering technology

and related science?

3 With respect to gauging

potential responses: What is

the level of awareness of

climate engineering technologies,

and what are attitudes

toward researching and

implementing them?

Science

Technology

Climate

Future

2010 - 2030

Report to Congressional Requester

Cover image from GAO represents gaseous carbon dioxide (CO

) molecules in ambient air, currently measured

at around 390 parts per million. Carbon dioxide consists of a central carbon atom doubly bonded with two

oxygen atoms (O=C=O). Carbon dioxide is colorless and odorless at room temperature. Plants consume CO

photosynthesis, which converts CO

into nutrients using energy from the Sun. Many scientists believe that the

increased atmospheric CO

concentration has increased the acidity of ocean waters and is the primary cause of

increased global average surface temperature. Global management of CO

and related risks underlies current ideas

about engineering the global climate system.

What GAO found

Climate engineering technologies do not now offer a viable response to global climate change.

Experts advocating research to develop and evaluate the technologies believe that research on

these technologies is urgently needed or would provide an insurance policy against worst case

climate scenarios—but caution that the misuse of research could bring new risks. Government

reports and the literature suggest that research progress will require not only technology studies

but also efforts to improve climate models and data.

The technologies being proposed have been categorized as carbon dioxide removal (CDR) and

solar radiation management (SRM). CDR would reduce the atmospheric concentration of

, allowing more heat to escape and thus cooling the Earth. For example, proposed CDR

technologies include enhancing the uptake of CO

in oceans and forests and capturing CO

from air chemically for storage underground. SRM technologies would place reflective material

in space or in Earth’s atmosphere to scatter or reflect sunlight (for example, by injecting sulfate

aerosols into the stratosphere to scatter incoming solar radiation or brightening clouds) or would

increase the planet’s reflectivity (for example, by painting roofs and pavements in light colors).

(See figure.)

Examples of climate engineering technologies. Source: GAO.

GAO found these technologies currently immature, many with potentially negative consequences.

Some studies say, for example, that stratospheric aerosols might greatly reduce summer

precipitation in places such as India and northern China.

Many experts advocated research because of its potential benefits but also recognized its risks.

For example, a country might unilaterally deploy a technology with a transboundary effect.

Research advocates emphasized the need for risk management, envisioning a federal research

effort that would (1) focus internationally on transparency and cooperation, given transboundary

effects; (2) enable the public and national leaders to consider issues before they become crises;

and (3) anticipate opportunities and risks. A small number of those we consulted opposed

research; they anticipated major technology risks or limited future climate change.

Based on GAO’s survey, a majority of U.S. adults are not familiar with climate engineering.

When given information on the technologies, they tend to be open to research but concerned

about safety.

Why GAO did this study

Reports of rising global temperatures

have raised questions about responses

to climate change, including efforts

to (1) reduce carbon dioxide (CO

)

emissions, (2) adapt to climate

change, and (3) design and develop

climate engineering technologies for

deliberate, large-scale intervention in

Earth’s climate.

Reporting earlier that the nation lacks

a coordinated climate-change strategy

that includes climate engineering,

GAO now assesses climate engineering

technologies, focusing on their

technical status, future directions

for research on them, and potential

responses.

To perform this technology assessment,

GAO reviewed the peer-reviewed

scientific literature and government

reports, consulted experts with a wide

variety of backgrounds and viewpoints,

and surveyed 1,006 adults across

the United States. Experts convened

with the assistance of the National

Academy of Sciences advised GAO, and

several reviewed a draft of this report.

GAO incorporated their technical and

other comments in the final report as

appropriate.

View GAO-11-71 or key components at

www.gao.gov. For more information,

contact Timothy Persons at (202)

512-6412 or [email protected].

Report multimedia

Depiction of the global carbon

cycle changes over time

www.gao.gov/multimedia/

interactive/GAO-11-71a

Global average energy budget of

the Earth’s atmosphere

www.gao.gov/multimedia/

interactive/GAO-11-71b

Highlights of GAO-11-71, a report

to the Ranking Member, Committee

on Science, Space, and Technology,

House of Representatives

Climate engineering

Technical status, future directions, and potential responses

TECHNOLOGY ASSESSMENT

GAO

Growing treestrees

rowing

Cloud brightening at sea

Capturing CO

from the air

Iron fertilization of

the ocean

Pumping liquid

CO into geological

formations

Aerosols in stratosphere

Light-colored roofs

and pavements

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TECHNOLOGY ASSESSMENT GAO-11-71

iii

July 28, 2011

The Honorable Eddie Bernice Johnson

Ranking Member

Committee on Science, Space, and Technology

House of Representatives

Dear Ms. Johnson:

In response to committee reports accompanying the legislative branch fiscal year 2008 appropriations bill,

the U.S. Government Accountability Office established a permanent operational technology assessment

group within GAO’s Applied Research and Methods team: the Center for Science, Technology,

and Engineering. Responding to your request that we conduct a technology assessment on proposed

technological approaches toward engineering the climate, we examined the current state of climate

engineering science and technology, experts’ views of the future of U.S. climate engineering research, and

potential public responses to climate engineering. We also discuss in this report key considerations for the

use of climate engineering technologies and their policy implications.

As agreed with your office, we plan no distribution of this report until 14 days after its issue date

unless you publicly announce its contents earlier. We will then send copies of this report to interested

congressional committees; the Secretaries of Agriculture, Commerce, Defense, Energy, and State;

the Administrator of the National Aeronautics and Space Administration; the Administrator of the

Environmental Protection Agency; and the Director of the National Science Foundation. We will provide

copies to others on request. In addition, the report will be available at no charge on the GAO website at

www.gao.gov.

If you have any questions concerning this report, you may contact me at (202) 512-6412 or

[email protected]. Contact points for our Offices of Congressional Relations and Public Affairs may

be found on the last page of this report. Major contributors to this report are listed on page 117.

Sincerely yours,

Timothy M. Persons, Ph.D.

Chief Scientist

GAO-11-71 TECHNOLOGY ASSESSMENT

TECHNOLOGY ASSESSMENT GAO-11-71

Summary

Reports of rising global average surface temperature have raised interest in the potential for engineering

Earth’s climate, supplementary to ongoing efforts to reduce greenhouse gas emissions and prepare for

climate change through adaptation. Proposed climate engineering technologies, or direct, deliberate,

large-scale interventions in Earth’s climate, generally aim at either carbon dioxide removal (CDR) or solar

radiation management (SRM). Whereas CDR would reduce the atmospheric concentration of carbon

dioxide (CO

), thus reducing greenhouse warming, SRM would either deflect sunlight before it reaches

Earth or otherwise cool Earth by increasing the reflectivity of its surface or atmosphere.

In conducting this technology assessment, we focused primarily on the technical status of climate

engineering and the views of a wide range of experts on the future of research.

Our findings indicate that

• climate engineering technologies are not now an option for addressing global climate change, given our

assessment of their maturity, potential effectiveness, cost factors, and potential consequences. Experts

told us that gaps in collecting and modeling climate data, identified in government and scientific

reports, are likely to limit progress in future climate engineering research.

• the majority of the experts we consulted supported starting significant climate engineering research now.

Advocates and opponents of research described concerns about its risks and the possible misuse of its

results. Research advocates supported balancing such concerns against the potential for reducing risks

from climate change. They further envisioned a future federal research effort that would emphasize risk

management, have an international focus, engage the public and national leaders, and anticipate new

trends and developments.

• asurvey of the public suggests that the public is open to climate engineering research butis concerned

about its possible harm and supports reducing CO

emissions.

Technical status

To assess the current state of climate engineering technology, we rated each technology for its maturity

on a scale of 1 to 9, using technology readiness levels (TRL)—a standard tool for assessing the readiness

of emerging technologies before full-fledged production or incorporation into an existing technology or

system. We found that climate engineering technologies are currently immature, based on the TRL scores

we calculated, and may face challenges with respect to potential effectiveness, cost factors, and potential

consequences. (We characterized a technology with a TRL score lower than 6 as immature.)

CDR technologies are designed to do one of the following: (1) chemically scrub CO

from the atmosphere

by direct air capture, followed by geologic sequestration of the removed CO

; (2) use biochar and biomass

The request for this assessment was originally made during the 111th Congress by the Chairman of the House Committee on

Science and Technology, who has since retired.

GAO-11-71 TECHNOLOGY ASSESSMENT

approaches to capture and sequester CO

; (3) manage land use to enhance the natural uptake and storage

of CO

; (4) accelerate CO

transfer from the atmosphere to the deep ocean for sequestration. We

scored all but one CDR technology at a maturity of TRL 2. This means that we found that scientific or

government publications have reported

• observation of the technology’s basic scientific principles through theoretical research or mathematical

models and

• conceptualization of an application of the technology in the context of addressing global climate

change—but not an analytic and experimental proof of concept.

The highest-scoring CDR technology (at TRL 3) was direct air capture of CO

, which has had

laboratory demonstrations using a prototype and field demonstrations of underground sequestration

of CO

. However, direct air capture is believed to be decades away from large-scale commercialization.

Additionally, for each of the currently proposed CDR technologies, we found that implementation on a

scale that could affect global climate change may be impractical, either because vast areas of land would be

required or because of inefficient processes, high cost, or unrealistically challenging logistics.

SRM technologies would inject aerosols into Earth’s stratosphere to scatter a fraction of incoming

sunlight, artificially brighten clouds, place solar radiation scatterers or reflectors in space, or increase the

reflectivity of Earth’s surface. All SRM technologies’ maturity measured TRL 2 or less. That is, none

had an analytical and experimental proof of concept. Additionally, we found that the SRM technologies

that we rated “potentially fully effective” have not, thus far, been shown to be without possibly serious

consequences. Further, each SRM technology must be maintained to sustain its effects on Earth’s

temperature; discontinuing the technology for any reason would result in Earth’s temperature rising to a

level dictated by other changes, such as an increased concentration of CO

in Earth’s atmosphere.

A key challenge in climate engineering research is safely evaluating the technologies’ potential risks in

advance of large-scale field tests or deployment. Climate modeling would be a helpful evaluative tool,

but a number of both federal agency and scientific reports have identified limitations in climate models

and their underlying bases. Expanded scientific knowledge, enhanced precision and accuracy of tools for

measuring key climate variables, and the development of dedicated high-performance computing would

help fill the gaps and make future research more effective.

Future directions

To determine how experts view the future of climate engineering research, we consulted 45 experts with

a wide range of backgrounds and professional affiliations. We used future scenarios developed by one set

of experts as a foresight tool to help elicit other experts’ views. We found that the majority of those we

consulted advocated starting significant research now or soon and believed that such research would have

the potential to help reduce future risks from climate change. However, some conditioned their advocacy

on the continuation of efforts to reduce emissions. Additionally, some pointed to new risks that the

research or technologies developed from it might introduce.

TECHNOLOGY ASSESSMENT GAO-11-71

vii

Many of the experts we consulted advocated research now because of their anticipation that substantial

progress toward effective technologies might require two or more decades. Others said that climate

engineering research is needed, even if future climate trends (such as the pace of change) are currently

uncertain, because such research represents “an insurance policy against the worst case [climate change]

scenarios.” Many of those who called for research now saw the situation as urgent, reflecting foresight

literature that warns against falling behind a potentially damaging trend—with possibly irreversible and

very costly consequences. Their view was that climate engineering research now would constitute timely

preparation for action and thus may help minimize the possibility of negative outcomes.

A small number of those we consulted opposed future research on climate engineering. Research

opponents reasoned that future climate change will not be great enough to warrant climate engineering or

that alternatives such as pursuing emissions reductions (without climate engineering) would be preferable.

However, the reason for opposing climate engineering research that was most strongly expressed

concerned the risks associated with the research itself or the technologies’ deployment.

Both research advocates and opponents cautioned that climate engineering research carries risks either

in conducting certain kinds of research or in using the results (for example, deploying potentially risky

technologies that were developed on the basis of the research). Some also noted that other nations are

conducting research and warned that, in the future, a single nation might unilaterally deploy a technology

with transboundary effects. The research advocates suggested managing risks from climate engineering by,

for example, conducting interdisciplinary risk assessments, developing norms and best practice guidelines

for open and safe research, evaluating deployment risks in advance—and, potentially, as we discuss below,

conducting joint research with other countries. Some advocates also indicated that rigorous research

could help reduce risks from the uninformed use of risky technologies (as, for example, might occur in a

perceived emergency) or emphasized the need to weigh potential risks from climate engineering against

risks from climate change.

Research advocates envisioned federal research that would foster developing and evaluating technologies

like CDR and SRM and emphasize risk management. The majority of research advocates supported

research that would include

• an international focus, sponsoring, for example, joint research with other nations (to foster cooperation

and shared norms) and the study of how one nation’s deployment might affect others, including those

that might respond negatively or be especially vulnerable;

• engagement with the public and U.S. decision-makers that might entail conducting studies to address

concerns and support decisions (for example, studies of economic, ethical, legal, and social issues and

studies of systemic risks); and

• foresight activities to help anticipate emerging research developments, key trends, and their implications

for climate engineering research—notably, the new or emerging opportunities and risks that such

changes might bring.

GAO-11-71 TECHNOLOGY ASSESSMENT

viii

Such features are broadly relevant to risk management in that they might (1) reduce risks of international

tensions or even conflict resulting from climate engineering, (2) help prepare the nation in advance of

possible crises, and (3) anticipate new risks that might be associated with future technologies.

The United States does not now have a coordinated federal approach to climate engineering research, and

we earlier recommended that such an approach be developed in the context of a federal strategy to address

climate change (GAO 2010a). Other approaches to addressing climate change include efforts to (1) reduce

emissions and (2) adapt to climate change.

Potential responses

To understand public opinion, we analyzed survey data from 1,006 adults 18 years old and older selected

to represent the U.S. population. We provided them with basic materials on climate engineering—that

is, information similar in amount and type to what they might receive in the news media. The materials

included a definition and examples of climate engineering technologies. Our survey revealed that a

majority of the U.S. population is not familiar with climate engineering but may be open to research.

Once provided with explanatory material, about 50–70 percent of the respondents across a range of

demographic groups would be open to research on climate engineering and about 45 percent would be

somewhat to extremely optimistic about its benefits. Such optimism would be tempered by caution, as we

estimate that about 50–75 percent of the U.S. adult public would be concerned about the technologies’

safety. Our survey results also indicate that support for reducing CO

emissions is more widespread than

support for climate engineering. About 65–75 percent of the public would support the involvement of

multiple organizations and interests in decision-making on these technologies. They included the scientific

community, a coalition of national governments, individual national governments, the general public,

private foundations, and not-for-profit organizations.

TECHNOLOGY ASSESSMENT GAO-11-71

Highlights i

Letter iii

Summary

1 Introduction 1

2 Background 9

3 The current state of climate engineering science and technology

3.1 Selected CDR technologies

3.1.1 Direct air capture of CO

with geologic sequestration 20

3.1.2 Bioenergy with CO

capture and sequestration 23

3.1.3 Biochar and biomass 25

3.1.4 Land-use management

3.1.5 Enhanced weathering

3.1.6 Ocean fertilization

3.2 Selected SRM technologies

3.2.1 Stratospheric aerosols

3.2.2 Cloud brightening

3.2.3 Scatterers or reflectors in space

3.2.4 Reflective deserts, flora, and habitats

3.3 Status of knowledge and tools for understanding climate engineering

3.3.1 Better models would help in evaluating climate engineering proposals

3.3.2 Key advancements in scientific knowledge could help improve climate models

3.3.3 Better observational networks could help resolve uncertainties in climate

engineering science 44

3.3.4 High-performance computing resources could help advance climate engineering science 46

4 Experts’ views of the future of climate engineering research

4.1 A majority of experts called for research now

4.2 Some experts opposed starting research

4.3 A majority of experts envisioned federal research with specific features

4.4 Some experts thought that uncertain trends might affect future research

5 Potential responses to climate engineering research

5.1 Unfamiliarity with geoengineering

5.2 Concern about harm and openness to research

5.3 Views on geoengineering in the context of climate and energy policy

5.4 Support for national and international cooperation on geoengineering

Contents

GAO-11-71 TECHNOLOGY ASSESSMENT

6 Conclusions 71

7 Experts’ review of a draft of this report

7.1 Our framing of the topic

7.2 Our assessment of the technologies

7.3 Our assessment of knowledge and tools for understanding climate engineering

7.4 Our foresight and survey methodologies

8 Appendices

8.1 Objectives, scope, and methodology

8.2 Experts we consulted on climate engineering technologies

8.3 Foresight scenarios

8.4 The six external experts who participated in building the scenarios

8.5 Experts who commented in response to the scenarios

100

8.6 Experts who participated in our meeting on climate engineering

102

8.7 Reviewers of the report draft

103

9 References

105

GAO contacts and staff acknowledgments

117

Related GAO products

118

Other GAO technology assessments

118

Figures

Figure 1.1 The Keeling curve, 1960–2010 1

Figure 1.2 Earth’s carbon cycle

Figure 2.1 Global average energy budget of Earth’s atmosphere

Figure 3.1 Capturing and absorbing CO

from air 20

Figure 3.2 CO

-absorbing synthetic tree 20

Figure 4.1 Taking early action to avoid potentially damaging trends: Illustration from

foresight literature 51

Figure 5.1 U.S. public support for actions on climate and energy, August 2010 67

Figure 5.2 U.S. public views on who should decide geoengineering technology’s use, August 2010 68

Figure 8.1 Four scenarios defining alternative possible futures

Tables and boxes

Table 1.1 Selected climate engineering proposals, 1877–1992 6-7

Table 3.1 Selected CDR technologies: Their maturity and a summary of available information 15-19

Table 3.2 Selected SRM technologies: Their maturity and a summary of available information 31-32

Table 5.1 Geoengineering types and examples given to survey respondents

Table 8.1 Nine technology readiness levels described 78-79

Box 4.1 Climate engineering research: Risk mitigation strategies from the literature 52

TECHNOLOGY ASSESSMENT GAO-11-71

AOGCM atmosphere-ocean general circulation model

BECS bioenergy with CO

capture and sequestration

CCS carbon capture and sequestration

CDR carbon dioxide removal

CLARREO Climate Absolute Radiance and Refractivity Observatory

DOE U.S. Department of Energy

EOR enhanced oil recovery

ESM Earth system model

GCM general circulation model

GPU graphics processing unit

IPCC Intergovernmental Panel on Climate Change

NAS National Academy of Sciences

NASA National Aeronautics and Space Administration

NETL National Energy Technology Laboratory

NIST National Institute of Standards and Technology

NOAA National Oceanic and Atmospheric Administration

NRC National Research Council

NSF National Science Foundation

PNNL Pacific Northwest National Laboratory

R&D research and development

SRM solar radiation management

TRL technology readiness level

USDA U.S. Department of Agriculture

Abbreviations

GAO-11-71 TECHNOLOGY ASSESSMENT

xii

TECHNOLOGY ASSESSMENT GAO-11-71

Every day, millions of tons of carbon-rich

compounds called fossil fuels are extracted,

refined or processed, and combusted to supply

the world with energy, releasing as a byproduct

millions of tons of carbon dioxide gas (CO

From 1900 to 2007, annual global CO

emissions from fossil fuel consumption increased,

on average, at a rate of about 2.6 percent

per year (Boden, Marland, and Andres 2010).

Fossil fuels, such as coal, oil, and methane, are natural organic

compounds of mostly carbon (C) and hydrogen (H). These

fuels are formed from dead plant and animal matter that

has been subjected to intense pressure and heat over geologic

time scales.

Compound annual growth rate calculated from available

emissions estimates.

As emissions increased, the atmospheric

concentration of CO

rose. Figure 1.1 shows the

rise in the concentration of CO

between 1960

and 2010 (Ralph Keeling 2011).

C. D. Keeling (1960), noting that CO

levels at

observation stations were increasing over time,

attributed this increase to fossil fuel combustion.

Although CO

is not the most abundant

Over time, atmospheric CO

can be reabsorbed as sediment

on the ocean floor through the carbon cycle.

In the atmosphere, greenhouse gases absorb and reemit

radiation within the thermal infrared range of the

electromagnetic spectrum. This is the fundamental cause of

the greenhouse effect, or the warming of Earth’s atmosphere.

In order of their prevalence by volume, the primary

greenhouse gases are water vapor (H

O), CO

, methane

(CH

), nitrous oxide (N

O), and ozone (O

) (Baird 1998).

Figure 1.1 The Keeling curve, 1960–2010. Source: GAO, adapted from Ralph Keeling (2011).

The orange line indicates the annual average atmospheric concentration of CO

derived from monthly in situ air

measurements at Mauna Loa Observatory, Hawaii. The cyclical pattern of the monthly measurements shown in light

grey indicates seasonal fluctuations. The approximate preindustrial concentration of 280 parts per million (ppm)

indicates the estimated atmospheric abundance of CO

around the year 1750. In 1960, the atmospheric concentration of

was about 317 ppm; by 2010, it had risen to about 390 ppm.

CO concentration (ppm)

280

300

320

340

360

380

400

1960 1970 1980 1990 2000 2010

Calendar year

Approximate

preindustrial

concentration

1 Introduction

GAO-11-71 TECHNOLOGY ASSESSMENT

greenhouse gas, many scientists have concluded

that CO

emitted by human activities is the

principal cause of the enhanced greenhouse effect

(Lacis et al. 2010).

Over the past century, global mean surface

temperature increased by about 0.75 degrees

Celsius, and many scientists expect the rise

to continue in coming decades (NRC 2010a;

Solomon et al. 2007), as we describe in the

background section of this report.

A few

scientists have argued that a doubling of the

atmospheric CO

concentration, by itself,

would increase the global average temperature

by only about 1 degree Celsius and that the

models predicting rising temperatures in

the coming decades are incomplete and are

therefore considerably uncertain (Lindzen 2010;

Lindzen and Choi 2009).

Nevertheless, there

is a consensus of many authoritative scientific

bodies, which have conveyed a sense of urgency

on the climate change issue; hence the following

discussion on climate engineering, or direct,

Water vapor (H

O) is the most abundant greenhouse gas

and has a powerful effect on warming (Solomon et al. 2007;

Kiehl and Trenberth 1997). Scientists have shown that

the tropospheric water vapor concentration significantly

affects the global average surface temperature. The enhanced

greenhouse effect caused by emissions from human activities

is sometimes called anthropogenic climate change. The

increased concentration of CO

is also known to be the

leading cause of another major environmental concern in

addition to warming: ocean acidification, manifested by

decreases in pH (hydrogen ion concentration), is caused

by the oceans’ greater uptake of atmospheric CO

as its

abundance increases (Sabine et al. 2004).

Multiple, interrelated systems can influence the enhanced

greenhouse effect.

These scientists argue that all current climate prediction

models incorrectly project more warming, based on positive

feedback from water vapor and clouds. Specifically, they

argue that such feedback has a negative effect (Lindzen

and Choi 2009). The Intergovernmental Panel on Climate

Change (IPCC) has also noted the uncertainty surrounding

such feedback (Solomon et al. 2007).

deliberate large-scale interventions in

Earth’s climate.

The future effects of warming are uncertain.

The National Research Council (NRC) recently

examined potential consequences of rising

temperatures over the next century, such as

changes in vegetation, precipitation, and the rate

of sea level rise (NRC 2010a). NRC’s report

suggests an overall potential for negative effects

on people, infrastructures, and ecosystems. For

example, the projected rise in sea level could

threaten several large ports and urban centers in

the United States, such as Miami, New York, and

Norfolk, as well as low-lying island groups, such

as the Maldives.

Some researchers have suggested

that climate change could have even more

extreme adverse consequences.

Others have

proposed that rising temperatures might benefit

certain geographic areas or economic sectors; for

example, agricultural productivity might increase

in some areas, although researchers caution that

how climate change affects agriculture is complex

and uncertain (Gornall et al. 2010). Additionally,

while global surface temperature is increasing on

average, it is not increasing uniformly (Solomon

et al. 2007). For example, scientists have observed

that temperatures have risen more in areas that

This report is an assessment of technologies to engineer the

climate and the quality of information available to assess these

technologies. In this report, we did not assess whether the

climate is changing or what is causing any climate change that

is occurring or whether current scientific knowledge supports

the notion that the climate is changing or its causes. We did

not assess whether climate change is or will be sufficient to

warrant using these technologies.

Mohamed Nasheed, President of the Maldives, has said that

sea level rise is already causing coastal erosion in his country,

evidenced by salt intrusion in the water table and relocations

affecting 16 islands (Eilperin 2010).

For example, climate change might lead to greater scarcity of

food, water, or shelter and social upheaval in many countries

in Africa, Asia, and the Middle East (CNA Corporation 2007,

44). Some have suggested that disrupted food and water

supplies in certain regions might lead to mass migrations or

international conflict (Dyer 2010).

TECHNOLOGY ASSESSMENT GAO-11-71

are relatively colder, and the observed change in

temperature is greater in winter than in summer

and greater at night than in the day (Solomon

et al. 2007). Disproportionate warming of cold

temperatures could have important implications

for human health and mortality, if exposure

to heat is less dangerous than exposure to cold

(NRC 2010a).

Two broad strategies to meet the challenges

of climate change through public policy are

mitigation and adaptation. Mitigation aims

to limit climate change, usually by decreasing

greenhouse gas emissions (GAO 2008a). For

example, mitigation might replace high-carbon

fuels, such as coal, with fuels that emit less

per unit of energy, such as natural gas.

Mitigation might also enhance the capacity of

sinks, which reabsorb CO

from the atmosphere

and store it on Earth (GAO 2008a). For example,

incremental changes in land use could increase

the amount of carbon stored as cellulosic fiber

in forests and other vegetation that removes

from the atmosphere by photosynthesis.

Adaptation aims to adjust Earth’s systems,

infrastructures, or social programs in response to

actual or expected changes in the climate.

For example, adaptation can make systems more

robust in the face of climatic extremes, exploit

new opportunities, or cope with adversity

(GAO 2009a).

Success in mitigating climate change or adapting

to it can depend on technological progress.

For example, the cost of mitigation is likely

to be lower if alternatives to fossil fuels are

less expensive (Popp 2006). Adaptation can

also be affected by the technology, as happens

in predicting the weather, controlling indoor

temperatures with heating and air conditioning,

or managing a sea level rise, as in building harbor

gates in Venice, Italy (Spencer et al. 2005).

However, neither mitigation nor adaptation

has progressed sufficiently to moderate current

climate projections or diminish the seriousness

of their effects. For example, the relative expense

of low-carbon energy technology presently tends

to limit its use. And requirements to reduce

emissions can be difficult to enforce, as the Kyoto

Protocol demonstrates, or can fail to encourage

advances in low-carbon energy technology

(Barrett 2008; Barrett 1998).

Even if deep emissions cuts were to stabilize the

atmospheric concentration of CO

at the current

level, scientific models predict that average global

surface temperature is likely to rise 0.3 to 0.9

degrees Celsius by 2100 (Backlund et al. 2008).

Some scientists suggest that climatic perturbation

from anthropogenic CO

emissions is nearing a

tipping point beyond which it will be difficult

or impossible to remediate changes in Earth’s

climate. Figure 1.2 illustrates Earth’s carbon

cycle, which regulates the flow of carbon between

the atmosphere and land-based and oceanic sinks.

These and other possible challenges to the

success of mitigation and adaptation have

helped stimulate public policy interest in

climate engineering, which would develop and

use technology to moderate Earth’s climate

by controlling the radiation balance and,

thus, average global temperature. The United

Kingdom’s Royal Society (the oldest scientific

academy in continuous existence) has identified

other distinguishing characteristics of this

strategy as well, highlighting the “deliberate,

large-scale intervention in the Earth’s climate

system” in its definition of geoengineering

(Royal Society 2009, ix).

We use the term “geoengineering” in appropriate contexts,

as when it refers to information we collected in a survey

of U.S. adults and their attitudes toward technologies to

address climate change. We described the alternative terms

“climate engineering,” “climate remediation,” and “climate

intervention” in a September 2010 report (GAO 2010a, 3).

GAO-11-71 TECHNOLOGY ASSESSMENT

In its 2009 report, the Royal Society described

two major approaches to climate engineering:

accelerating the movement of carbon from the

atmosphere to terrestrial and oceanic carbon

sinks, or carbon dioxide removal (CDR), and

controlling net incoming radiation from the Sun,

or solar radiation management (SRM). As CDR

reduces the atmospheric concentration of CO

the enhanced greenhouse effect is weakened,

and thermal radiation more easily escapes into

space.

SRM, in contrast, attempts to reduce net

Although experts differ on which technologies to define

as climate engineering (Gordon 2010, ii), in this report

we limited our assessment to key climate engineering

technologies among those reviewed by the Royal Society

(Royal Society 2009).

incoming solar radiation by deflecting sunlight or

by increasing the reflectivity of the atmosphere,

clouds, or Earth’s surface.

The concept of engineering the climate is not

new (Fleming 2010). Table 1.1 shows examples

of climate engineering proposals dating from

1877. Today, policymakers and scientists are

examining climate engineering as a way to

manage potential catastrophic risks from

climate change.

Because SRM would not affect the atmospheric concentration

of CO

, it would not abate increased ocean acidification.

Figure 1.2 Earth’s carbon cycle. Source: GAO, adapted from Sarmiento and Gruber (2002), updated

using Field, Sarmiento, and Hales (2007).

Note: All numeric values are in gigatons (GtC), or billions of metric tons, of carbon. In Earth’s carbon cycle, preindustrial

reservoir sizes are represented by black numbers. Cumulative postindustrial reservoir transfers are represented by

red numbers. Current fluxes between reservoirs are shown in smaller type; the largest flux is 6.4 GtC per year from

industrialization. This ongoing carbon imbalance is causing ocean water to become more acidic and is believed to be the

primary cause of increased global average surface temperature. (An animated depiction of changes in the global carbon

cycle over time may be accessed at www.gao.gov/multimedia/interactive/GAO-11-71a.)

TECHNOLOGY ASSESSMENT GAO-11-71

We designed this report to complement our

September 2010 report on geoengineering (GAO

2010a). In this context, we conducted this

technology assessment of climate engineering.

Our objectives for this report were to examine

(1) the current state of climate engineering

science and technology, (2) expert views of the

future of U.S. climate engineering research, and

(3) public perceptions of climate engineering

(we describe our methodology in section 8.1).

To determine the current state of the science

and technology of climate engineering, we

reviewed a broad range of scientific and

engineering literature, including proceedings

from conferences such as the 2010 Asilomar

International Conference on Climate

Intervention Technologies (Asilomar Scientific

Organizing Committee 2010). We revisited

GAO-10-903, a complementary report on

climate engineering we issued in September

2010 (GAO 2010a). We reviewed relevant

congressional testimony. We interviewed a broad

range of experts and officials working on climate

engineering and proponents of specific climate

engineering technologies. This report is an

In the Senate report accompanying the proposed bill for

the legislative branch fiscal year 2008 appropriation, the

Senate Committee on Appropriations recommended the

establishment of a permanent technology assessment function

within GAO (United States Senate 2007, see S. Rep. No.

110-89, at 42–43 (2007)). The House Committee on

Appropriations, in providing funding to GAO to perform

technology assessment studies, noted that “it is necessary for

the Congress to equip itself with effective means for securing

competent, timely and unbiased information concerning the

effects of scientific and technical developments and use the

information in the legislative assessment of matters pending

before the Congress” (U.S. House of Representatives 2007,

see H.R. Rep. No. 110-198, at 30 (2007)). GAO established a

permanent operational technology assessment group within its

Applied Research and Methods team: the Center for Science,

Technology, and Engineering. GAO defines technology

assessment as the thorough and balanced analysis of significant

primary, secondary, indirect, and delayed interactions of a

technological innovation with society, the environment, and

the economy and the present and foreseen consequences and

effects of those interactions.

assessment of technologies to engineer the climate

and the quality of information available to assess

these technologies. We did not independently

assess whether climate change is occurring

or what is causing any climate change if it is

occurring or whether current scientific knowledge

supports the occurrence of climate change or

its causes. We did not assess whether climate

changes are or will be sufficient to warrant using

these technologies.

To ensure a balance of views and information,

we analyzed and synthesized information from

an array of experts with diverse views on our

subject. We used the Royal Society’s classification

of climate engineering approaches to focus our

analysis on CDR and SRM technologies

(Royal Society 2009, 1). From the information

we found in the literature and our interviews

with experts, we assessed climate engineering

technologies along four key dimensions:

(1) maturity, (2) potential effectiveness, (3) cost

factors, and (4) potential consequences. We did

not independently assess the accuracy of the cost

estimates, but we report estimates we found in

the literature.

To assess how experts view the future of climate

engineering research, we (1) conducted a foresight

exercise in which experts developed alternative

future scenarios; (2) elicited comments,

stimulated by the scenarios, from a broad array of

experts; and (3) asked other experts to respond to

the preliminary synthesis we developed from the

scenarios and earlier comments.

GAO-11-71 TECHNOLOGY ASSESSMENT

Date Who Proposal

1877

Nathaniel Shaler,

American scientist

Suggested rerouting the Pacific’s warm Kuroshio Current

through the Bering Strait to raise Arctic temperatures as

much as 30 degrees Fahrenheit

1912

Carroll Livingston

Riker, American

engineer, and

William M. Calder,

U.S. Senator

Proposed building a 200-mile jetty into the Atlantic Ocean to

divert the warm Gulf Stream over the colder Labrador current

to change the climate of North America’s Atlantic Coast;

Calder introduced a bill to study its feasibility

1929

Hermann Oberth,

German-Hungarian

physicist and engineer

Proposed building giant mirrors on a space station to focus

the Sun’s radiation on Earth’s surface, making the far North

habitable and freeing sea lanes to Siberian harbors

1945

Julian Huxley,

biologist and

Secretary-General of

UNESCO 1946–48

Proposed exploding atomic bombs at an appropriate height

above the polar regions to raise the temperature of the

Arctic Ocean and warm the entire climate of the northern

temperate zones

c. 1958

Arkady Markin,

Soviet engineer

Proposed that the United States and Soviet Union build a

gigantic dam across the Bering Strait and use nuclear

power–driven propeller pumps to push the warm Pacific

current into the Atlantic by way of the Arctic Sea. Arctic ice

would melt, and the Siberian and North American frozen

areas would become temperate and productive

1958

M. Gorodsky,

Soviet engineer and

mathematician, and

Valentin Cherenkov,

Soviet meteorologist

Proposed placing a ring of metallic potassium particles into

Earth’s polar orbit to diffuse light reaching Earth and increase

solar radiation to thaw the permanently frozen soil of Russia,

Canada, and Alaska and melt polar ice

1965

President’s Science

Advisory Committee,

United States

Investigated injecting condensation or freezing nuclei into the

atmosphere to counteract the effects of increasing

carbon dioxide

1977

Cesare Marchetti,

Italian industrial

physicist

Coined the term “geoengineering” and proposed sequestering

in the deep ocean

Table 1.1 Selected climate engineering proposals, continues on next page

TECHNOLOGY ASSESSMENT GAO-11-71

We also conducted focus groups and a web-

based survey of the U.S. adult population. We

surveyed a representative sample of U.S. residents

18 years old and older from July 19 to

August 5, 2010, receiving usable responses

from 1,006 respondents. We used the term

“geoengineering” in the information we gave the

focus group and survey participants, given that

we and others, such as the Royal Society, had

used this term earlier.

We convened a meeting of scientists, engineers,

and other experts, with the assistance of the

National Academy of Sciences (NAS), that we

called the Meeting on Climate Engineering.

We helped NAS select a diverse and balanced

group of participants with expertise in climate

engineering, climate science, measurement

science, foresight studies, emerging technologies,

research strategies, and the international, public

opinion, and public engagement dimensions of

climate engineering. We provided them with the

preliminary results of our work, and the meeting

served as a forum in which the participants

expressed general reactions to and gave advice and

suggestions on our preliminary findings. Their

comments led us to review additional published

and unpublished literature.

Table 1.1 Selected climate engineering proposals, 1877–1992. Source: GAO.

Note: Table 1.1 is based in part on an outline provided by James R. Fleming. We selected proposals beginning in the

19th century to illustrate a variety of climate engineering technologies and points in Earth’s climate system where

interventions could occur. The table excludes numerous proposals to generate rain or alter hurricanes, which are not

intended to cause long-term change.

Date Who Proposal

1983

Stanford Penner,

A. M. Schneider, and

E. M. Kennedy,

American physicists

Suggested introducing small particles into the atmosphere to

reflect more sunlight back into space

1988

John H. Martin,

American

oceanographer

Proposed dispersing a relatively small amount of iron into

appropriate areas of the ocean to create large algae blooms

that could take in enough atmospheric carbon to reverse the

greenhouse effect and cool Earth

1989

James T. Early,

American

climatologist

Suggested deflecting sunlight by 2 percent with a $1 trillion to

$10 trillion “space shade” placed in Earth orbit

1990

John Latham, British

cloud physicist

Proposed seeding marine stratocumulus clouds with seawater

droplets to increase their reflectivity and longevity

1992

NAS Committee on

Science, Engineering,

and Public Policy

Proposed adding more dust to naturally occurring stratospheric

dust to increase the net reflection of sunlight

GAO-11-71 TECHNOLOGY ASSESSMENT

Following the meeting, we contacted the

participants in person or by telephone or e-mail

to clarify and expand what we had heard.

We used what we learned from the meeting

participants to update and clarify our exposition

of the current state of climate engineering

technology, expert views of the future of

U.S. climate engineering research, and public

perceptions of climate engineering. We then sent

a complete draft of our report to the participants

in the Meeting on Climate Engineering who had

agreed to review it.

We conducted our work for this technology

assessment from January 2010 through July 2011

in accordance with GAO’s quality standards as

they pertain to technology assessments. Those

standards require that we plan and perform the

technology assessment to obtain sufficient and

appropriate evidence to provide a reasonable basis

for our findings and conclusions, based on our

technology assessment objectives. We believe that

the evidence we obtained provides a reasonable

basis for our findings and conclusions, based on

our technology assessment objectives.

TECHNOLOGY ASSESSMENT GAO-11-71

Global temperature increases such as those

measured on Earth have been attributed to a

gradual change in the balance of energy flowing

into and away from Earth’s surface. Earth’s

system maintains a constant average temperature

only if the same amount of energy leaves the

system as enters it. If more energy enters than

leaves, the difference manifests as a temperature

increase. Figure 2.1 shows current estimates of

the equilibrium transfer of energy.

Solar radiation is the predominant source of

energy entering Earth’s system. It has an average

global power of approximately 342 watts per

square meter (W/m

). The system, including

Earth’s surface and the atmosphere, absorbs

about 69 percent of incoming solar radiation and

reflects the remaining 31 percent back into space.

That is, Earth’s surface absorbs about 49 percent

of incoming radiation, and the atmosphere

absorbs about 20 percent. Earth’s atmosphere

Figure 2.1 Global average energy budget of Earth’s atmosphere. Source: GAO, adapted from

Kiehl and Trenberth 1997.

Note: All numeric values are in watts per square meter (W/m

). Incoming sunlight is both reflected from and absorbed

by the atmosphere, clouds, and Earth’s surface. Some of the energy absorbed by Earth’s surface is transferred to the

atmosphere by evaporation and convection, and the remainder is emitted as heat energy. The majority of the heat

energy is absorbed by the atmosphere and clouds, with some escaping directly to space. Energy absorbed by the

atmosphere and clouds is reradiated as heat energy back to Earth’s surface as well as directly to space. Based on the

composition of the atmosphere and clouds, the heat energy they absorb can accumulate by the greenhouse effect in

which energy emitted from Earth’s surface is trapped by gases in the atmosphere and clouds. For this reason, greenhouse

gases in Earth’s atmosphere can affect global average surface temperature. (An animated depiction of the global average

energy budget of Earth’s atmosphere may be viewed at www.gao.gov/multimedia/interactive/GAO-11-71b.)

2 Background

GAO-11-71 TECHNOLOGY ASSESSMENT

and clouds reflect approximately 23 percent into

space, while Earth’s surface (land, vegetation,

water, and ice) reflects approximately 9 percent.

Energy absorbed by the atmosphere affects the

planet’s climate system through subsequent

energy transfers (Solomon et al. 2007).

The energy Earth’s surface and atmosphere

absorb warms the planet. An inflow of energy to

Earth without an equivalent outflow would result

in continually increasing temperatures. However,

Earth reemits energy from the surface to the

atmosphere in the form of thermal radiation

(long wavelength or infrared radiation)

(Solomon et al. 2007).

Approximately 10 percent of the thermal

radiation reemitted by Earth passes through

the atmosphere into space, and 90 percent

is absorbed in the atmosphere, primarily in

greenhouse gases, which efficiently absorb long-

wave radiation. The atmospheric concentration of

greenhouse gases is very low. Water vapor (H

is the most important greenhouse gas and is

highly variable but typically makes up about

1 percent of the atmosphere (Solomon et al.

2010; Kiehl and Trenberth 1997). Carbon

dioxide is the second most important greenhouse

gas; the current atmospheric concentration of

is approximately 390 ppm (R. F. Keeling

et al. 2009; Kiehl and Trenberth 1997;

C. D. Keeling et al. 2001).

Just as the planet must maintain a balance of

incoming and outgoing energy, the atmosphere

and clouds must emit as much energy as they

absorb to maintain a constant temperature.

Therefore, the atmosphere and clouds emit

Energy is also transferred mechanically (not by radiation) from

Earth’s surface to the atmosphere and clouds by evaporation

and convection.

long-wave radiation at approximately the same

rate as they absorb energy from the Sun and

Earth. This is manifested as additional thermal

emissions both into space and toward Earth.

The planet’s surface absorbs the Earth-bound

thermal radiation, which raises Earth’s surface

temperature, which increases thermal radiation

from Earth’s surface, and so on, until this

feedback achieves stable temperatures.

The relationship between temperature and

thermal radiation emitted from Earth is

approximately described by the Stefan-

Boltzmann law:

where F is the thermal radiation emitted from

Earth’s surface in watts per square meter (W/m

is the Stefan-Boltzmann constant, and T is the

temperature of Earth’s surface in Kelvin (K).

The Stefan-Boltzmann law provides evidence for

atmospheric greenhouse gas feedback in Earth’s

energy system. If Earth’s radiation, absorbed and

reemitted, were only 235 W/m

(342 W/m

minus 107 W/m

of reflected solar radiation), its

average surface temperature would be about

254 K (–19 degrees Celsius). But Hansen and

colleagues have estimated that Earth’s actual

average surface air temperature between 1951 and

1980 was approximately 287 K (14 degrees

Celsius) (Hansen et al. 2010). The difference in

temperature is attributed to greenhouse gases that

trap thermal radiation, warming Earth as

depicted in figure 2.1. Thermal radiation emitted

The Stefan-Boltzmann law, named after Jožef Stefan and

Ludwig Boltzmann, states that the total power radiated per

unit of surface area of a black body per unit of time is directly

proportional to the fourth power of the black body’s

thermodynamic temperature T. The Stefan–Boltzmann

constant

is equal to 5.6704 x 10

–8

watts per square meter

per absolute temperature measured in Kelvin to the fourth

power (W/m

F = σ T

TECHNOLOGY ASSESSMENT GAO-11-71

by Earth’s surface at 287 K is 385 W/m

, which

compares favorably with the 390 W/m

in the

figure, corresponding to a temperature of 288 K.

Climate scientists infer that accumulations of

anthropogenic greenhouse gases are gradually

adding to Earth’s natural greenhouse process.

These accumulations absorb more thermal

radiation emitted by Earth’s surface and reduce

thermal radiation that escapes into space. The

additional thermal radiation the greenhouse gases

absorb is reradiated to space and back toward

Earth. The planet’s surface absorbs the additional

Earth-bound thermal radiation, which raises

Earth’s surface temperature, which increases

thermal radiation from Earth’s surface, and so

on, until this feedback achieves a new, higher

stable temperature. The magnitude and effect

of this change in Earth’s global energy system

are important subjects of climate science studies

today (Solomon et al. 2007; NRC 2010a).

GAO-11-71 TECHNOLOGY ASSESSMENT

TECHNOLOGY ASSESSMENT GAO-11-71

Most climate engineering proposals would aim

to remediate the climate by affecting Earth’s

energy balance, using either CDR to reduce

the atmospheric concentration of CO

or SRM

to reduce incoming solar radiation. These two

approaches differ significantly in their technical

challenges and potential consequences (Royal

Society 2009). The literature and our interviews

with experts suggested four key dimensions on

which we assessed these technologies, to

the extent possible, given their current

development: (1) maturity, (2) potential

effectiveness, (3) cost factors, and (4) potential

consequences (see section 8.1). Since developing

many of the technologies we examined would

require advances in new scientific data and

analyses, we identified the climate’s representative

physical, chemical, and biological algorithms;

the geographic, temporal, and technical

sensors of essential climate mechanisms; and

next-generation, high-performance computing

resources dedicated to climate science as areas

that represent current shortfalls in knowledge

and infrastructure.

CDR technologies may be characterized as

predominantly land-based or predominantly

ocean-based (NRC 2010a; Royal Society

2009). Land-based technologies include direct

air capture, bioenergy with CO

capture and

sequestration, biochar and other biomass-related

methods, land-use management, and enhanced

weathering. Direct air-capture systems attempt to

capture CO

from air directly and then store it in

deep subsurface geologic formations. Bioenergy

with CO

capture and sequestration would also

store CO

underground, and biochar and other

biomass-related methods would sequester carbon

in soil or bury it. Land-use management practices

we reviewed would enhance natural sequestration

of CO

in forests. Enhanced weathering would fix

atmospheric CO

in silicate rocks in a chemical

reaction and then store it as either carbonate

rock or dissolved bicarbonate in the ocean.

Ocean-based technologies would fertilize the

ocean to promote the growth of phytoplankton

to sequester CO

Seven SRM technologies have been reported in

sufficient detail for us to assess them as candidates

for climate engineering. Two would be deployed

in the atmosphere—one scattering solar radiation

back into space using stratospheric aerosols, the

other reflecting solar radiation by brightening

marine clouds. Two would be deployed in

space—one scattering or reflecting solar radiation

from Earth orbit, the other scattering or reflecting

solar radiation at a stable position between Earth

and the Sun. The three remaining technologies

would artificially reflect additional solar radiation

from Earth’s surfaces—covered deserts, more

reflective flora, or more reflective settled areas.

We found that since most climate engineering

technologies are in early stages of development,

none could be used to engineer the climate on

a large scale at this time. We used technology

readiness levels to rate the maturity of each

technology on a scale from 1 to 9, with scores

lower than TRL 6 indicating an immature

3 The current state of climate engineering

science and technology

GAO-11-71 TECHNOLOGY ASSESSMENT

technology. No CDR technology scored higher

than TRL 3, and no SRM technology scored

higher than TRL 2.

Considerable uncertainty surrounds the potential

effectiveness of the technologies we reviewed, in

part because they are immature. Additionally, for

several proposed CDR technologies, the amount

of CO

removed may be difficult to verify

through modeling or direct measurements.

The technologies’ cost factors we report represent,

for CDR, resources used to remove CO

from the

atmosphere and store it. For SRM, they represent

resources required to counteract global warming

caused by doubling the preindustrial atmospheric

concentration of CO

or, for technologies that are

potentially not fully effective, resources required

to counteract global warming to the maximum

extent possible. Some of the studies we reviewed

indicate possible cost levels; we report these

for illustration, but we did not evaluate them

independently. Some studies described cost levels

qualitatively (Royal Society 2009).

Using many of the CDR and SRM technologies

we reviewed would pose risks, some of which

might not yet be known. Although minimal risks

have been reported for air capture, some risks

are related to the geologic sequestration of CO

Land-use management approaches to capture

and store CO

are not generally regarded as risky.

Enhanced weathering would pose environmental

risks from the large-scale mining activities that

would be needed to support it. The short-term

We used the AFRL Technology Readiness Level Calculator

to assess maturity (see section 8.1). For a rating of TRL 2

or higher, the basic requirement is a system concept on a

global scale; for a rating of TRL 3 or higher, analytical and

experimental demonstration of proof of concept is required,

and for a rating of TRL 4 or higher, system demonstration

with a breadboard unit is required. These requirements apply

regardless of a technology’s scientific basis or the extent to

which the techniques it incorporates are well established.

and long-term ecological, economic, and

climatologic risks from ocean fertilization remain

uncertain. Using SRM technologies could

affect temperatures but would not abate ocean

acidification. Potential effects on precipitation

are varied. Failing to sustain SRM technologies,

once deployed, could result in a potentially rapid

temperature rise.

In sections 3.1 and 3.2, we present our

assessment of the CDR and SRM technologies.

In section 3.3, we describe the status of scientific

knowledge and infrastructure related to climate

engineering technologies.

3.1 Selected CDR technologies

Table 3.1 summarizes our assessment of the

maturity of six CDR technologies and presents

information from published reports on their

potential effectiveness, cost factors, and potential

consequences. TRL ratings assess the maturity

of each technology. Potential effectiveness is

described in terms of an overall qualitative rating,

where possible, and quantitative estimates of

(1) the maximum capacity to reduce the global

atmospheric concentration of CO

(ppm) from

its projected level of 500 ppm in 2100 and

(2) the annual capacity to remove CO

from

Earth’s atmosphere (gigatons of CO

or CO

-C

equivalent per year), which we compared to

annual anthropogenic emissions of 33 gigatons

of CO

Cost factors represent the resources

used to remove CO

from the atmosphere and

store it. Potential consequences associated with

each technology include reported negative

consequences, risks, and cobenefits.

In 2010, the atmospheric concentration of CO

was about

390 ppm; around the year 1750, it was about 280 ppm.

TECHNOLOGY ASSESSMENT GAO-11-71

Technology Maturity

Potential

effectiveness

Cost factors

Potential

consequences

Direct air

capture of CO

with geologic

sequestration

Low (TRL 3):

• Basic principles understood

and reported

• System concept formulated

• Experimental proof of

concept demonstrated

with a prototype unit in a

laboratory environment

• Models of CO

injection

and transport developed

and used for risk analysis

and for simulating fate of

injected CO

• Basic technological

components not

demonstrated as

working together

• No plans or prototypes

for large-scale industrial

implementation

• Geological sequestration

of CO

is more mature but

not practiced on a scale to

potentially affect climate

Not rated:

• No “obvious limit” to

the amount of CO

reduction by year 2100

• Could theoretically

counter all global

anthropogenic CO

emissions at 33 gigatons

per year

• Large energy penalty:

net increase in CO

emissions if fossil fuel

used (electricity from

fossil fuels would release

more CO

than an air

capture unit would

remove)

• Uncertainty around

technical scalability

• Viability may depend on

nature and extent of a carbon

market

• Process energy requirements

for currently inefficient

technologies for directly

separating CO

from air in

very dilute concentration

• Transportation and logistics

for sequestration of captured

• Construction and

management of geologic

sequestration sites (e.g.,

injection, measuring,

monitoring, and verification)

• Greatly varied estimates in

the scientific literature: $27

to $630 or more per ton of

removed (excluding

transportation, sequestration,

and other costs)

• Aspects associated with

handling process materials

or chemicals

• May have sequestration

risks such as potential

for CO

to escape from

underground storage in

the event of reservoir

fracture or fissure from

built-up pressure

Table 3.1 Selected CDR technologies, continues on next page

GAO-11-71 TECHNOLOGY ASSESSMENT

Technology Maturity

Potential

effectiveness

Cost factors

Potential

consequences

Bioenergy with

capture and

sequestration

Low (TRL 2):

• Basic principles understood

and reported

• System concept formulated

• No experimental

demonstration of proof

of concept (no laboratory

scale experiments that

indicate CO

reducing

potential)

• Emerging technology

leverages what is known

about CO

capture and

geologic sequestration

Low to medium:

• Maximum ability to

reduce atmospheric

: 50–150 ppm

by 2100

• Net carbon negative

under ideal conditions

• Depends on plant

productivity and land

area cultivated

• Viability may depend on

nature and extent of a

carbon market

• Value of land in other uses

• Potentially large land area

for growing and harvesting

biomass

• Type of biomass feedstock

(e.g., switchgrass)

• Process energy requirements

for bioenergy production

(e.g., pyrolysis)

• Construction and

management of geologic

sequestration sites (e.g.,

injection, measuring,

monitoring, and verification)

• Transportation and logistics

for sequestering captured CO

• Greatly varied estimates in the

scientific literature: $150–

$500 per ton of CO

removed

(excluding transportation and

sequestration costs)

• Potential land-use

trade-offs; related impacts

on food prices, water

resources, fertilizer use

• CO

sequestration risks

same as direct air capture

Table 3.1 Selected CDR technologies, continues on next page

TECHNOLOGY ASSESSMENT GAO-11-71

Technology Maturity

Potential

effectiveness

Cost factors

Potential

consequences

Biochar and

biomass

methods

Low (TRL 2):

• Basic principles understood

and reported

• System concept formulated

• Proof of concept shown in

modeling and experimental

results demonstrating its

capturing ability–but

sequestration aspects

uncertain

• Not practiced on a scale to

affect climate. No plans or

prototypes for large-scale

implementation

• Substantial uncertainties

about capacity to reduce

net emissions of CO

Low:

• Maximum ability to

reduce atmospheric

: 10–50 ppm

by 2100

• Maximum annual

sustainable reduction:

1–2 gigatons CO

-C

equivalent of CO

, and N

• Net carbon negative

under ideal conditions

(comparable to

bioenergy with

capture and

sequestration)

• Viability may depend on

nature and extent of a

carbon market

• Soil fertility outcomes

• Type of pyrolysis feedstock

and related factors

• Process energy requirements

for bioenergy production

(e.g., pyrolysis)

• Greatly varied estimates in

the scientific literature:

$2–$62 per ton of CO

removed

• Potential land-use

trade-offs

• Long-term effects on

soil uncertain

• Health and safety of

pyrolysis and biochar

handling

• Local benefits to soil

enhance crop yield

Table 3.1 Selected CDR technologies, continues on next page

GAO-11-71 TECHNOLOGY ASSESSMENT

Technology Maturity

Potential

effectiveness

Cost factors

Potential

consequences

Land-use

management

(reforestation,

afforestation,

or reductions in

deforestation)

Low (TRL 2):

• Basic principles understood

and reported

• Techniques well established

• System concept formulated

and estimates of its carbon

mitigation potential

reported based on

modeling studies

• No experimental

demonstration or proof

of systemwide concept

of CO

capture and

sequestration by land-use

activities

• Not practiced on a scale to

affect climate. No plans for

large-scale implementation

Low to medium:

• Potential removal of

1.3–13.8 gigatons CO

annually

• 0.4–14.2 metric tons

of CO

sequestered per

acre per year

• Possible rerelease of

sequestered CO

• Viability may depend on

nature and extent of a carbon

market

• Value of land in other uses

• Potentially large land area for

growing or preserving forests

• Type of flora planted or

preserved

• Natural resource requirements

for maintenance and

management of forests

(e.g., water)

• Measuring, monitoring, and

verification

• Potential land-use

trade-offs

• Possible cobenefits

such as reduced

water runoff

Enhanced

weathering

Low (TRL 2):

• Basic principles understood

and reported

• System concept formulated

• No experimental

demonstration of proof of

system-wide concept

• Not practiced on a scale to

affect climate. No plans or

prototypes for large-scale

implementation

Not rated:

• Limited studies in

literature

• Some estimates based

on models but varied

conclusions about levels

of effectiveness

• Viability may depend on

nature and extent of a carbon

market

• Design and implementation

of silicate-based weathering

scheme, including

distribution and delivery of

material

• Mining and transportation of

silicate rock, and logistics

• Greatly varied estimates in the

scientific literature: $4–$100

per ton of CO

removed

• Potentially undesirable

environmental and other

consequences from

large-scale mining and

transportation

Table 3.1 Selected CDR technologies, continues on next page

TECHNOLOGY ASSESSMENT GAO-11-71

Technology Maturity

Potential

effectiveness

Cost factors

Potential

consequences

Ocean

fertilization

Low (TRL 2):

• Basic principles understood

and reported

• System concept formulated

• Limited small-scale field

experiments conducted but

results unclear

• Published research mainly

theoretical

• Not practiced on a scale to

affect climate. No plans or

prototypes for large-scale

implementation

Low:

• Maximum ability to

reduce atmospheric

: 10–30 ppm by

2100

• Scientific uncertainty

surrounding (1)

duration of carbon

sequestered in

the ocean, (2)

how ecological

impacts might limit

effectiveness, and (3)

how often iron would

need to be added

• Outcomes from

limited experiments

not understood or well

documented

• Viability may depend on

nature and extent of a carbon

market

• Design and implementation

of ocean fertilization scheme,

including distribution and

delivery of material

• Mining and transportation of

iron ore, and logistics

• Greatly varied estimates in the

scientific literature: $8–$80

per ton of CO

removed

• Ecological effect on

ocean not well

understood

• Risk of algal blooms

causing anoxic zones

in the ocean

Table 3.1 Selected CDR technologies: Their maturity and a summary of available information. Source: GAO.

In this report, we considered each technology’s maturity in terms of its readiness for application in a system designed to address global climate change. To do this, we used technology readiness levels

(TRL), a standard tool that some federal agencies use to assess the maturity of emerging technologies. We characterized technologies with TRL scores lower than 6 as “immature” (section 8.1). The TRL

rating methodology considers the maturity level of the whole integrated system rather than individual components of a particular technology.

We assessed potential effectiveness by considering the qualitative judgments of the Royal Society and reported estimates of two quantitative measures: (1) maximum ability to reduce the atmospheric

(ppm) projected for 2100 and (2) annual capacity to remove CO

from Earth’s atmosphere (gigatons of CO

or CO

-C equivalent per year). Additionally, we reviewed scientific literature with respect

to these measures of effectiveness and for assessments indicating the feasibility of implementing CDR technologies on a global scale to achieve a net reduction of atmospheric CO

concentration. A

technology was not assigned an overall qualitative rating when there were substantial uncertainties in the literature about its effectiveness (see section 8.1).

Cost factors are resources a system uses to remove CO

from the atmosphere and store it. Some of the studies we reviewed indicated possible cost levels, which we provide here for illustration. We did

not evaluate this information independently.

Includes potential consequences, risks, and cobenefits.

GAO-11-71 TECHNOLOGY ASSESSMENT

3.1.1 Direct air capture of CO

with geologic sequestration

3.1.1.1 What it is

Direct air capture would chemically scrub CO

directly from the atmosphere. In some conceptual

designs, air is brought into contact with a

-absorbing liquid solution containing sodium

hydroxide or with a solid sorbent in the form of

a synthetic ion-exchange resin that selectively

absorbs CO

gas.

Figures 3.1 and 3.2 illustrate

two different air-capture units. Figure 3.1 shows

an artist’s rendering of the air-contactor design,

and figure 3.2 illustrates a CO

-absorbing

synthetic tree made from a proprietary resin.

A CO

-absorbing resin (sorbent material) could

be shaped as a tree or as packing material placed

inside a large column where it would be brought

into contact with air. The CO

-rich solution or

synthetic resin would be sent to a regenerator,

where the CO

would be separated from the

liquid by thermal cycling or by exposure to

humid air. The resulting concentrated stream

of CO

could be compressed to liquid form

and delivered (by trucks, ships, or pipelines)

to a sequestration site.

The sorbent would be

recycled to capture additional CO

Experts have proposed the compression and

transportation of captured CO

for sequestration

in deep underground geologic or saline

formations. Most candidate geologic formations

consist of layers of porous underground rock

capped by layers of nonporous rock that would

keep the injected fluids trapped in the lower

pore spaces. The CO

would be compressed

under elevated pressure (greater than 2,000 psi,

Sorbent refers to a solution or solid that selectively

absorbs a specific gas.

Geologic sequestration of CO

is a relatively new idea.

or 13 megapascals (MPa)) and sequestered at

the capture site, on shore, or in the deep ocean,

where the hydrostatic head of the sea water above

would keep the CO

from rising to the surface

(DOE 2006).

Note: This is a virtual rendering of an air-capture

unit designed by Carbon Engineering Ltd. Each

such unit would capture about 100,000 tons of

per year. A battery of such units is intended

to work with a chemical recovery plant to

produce high-purity CO

Figure 3.1 Capturing and absorbing CO

from air.

Source: Carbon Engineering Ltd.

Figure 3.2 CO

-absorbing synthetic tree.

Source: Columbia University.

Note: This is a

synthetic tree made

from a proprietary

resin that can absorb

from air.

Psi indicates pounds per square inch. A megapascal is

1 million pascals; a pascal is a measure of force per unit

area, defined as 1 newton per square meter. A newton is the

force that produces an acceleration of 1 meter per second per

second when exerted on a mass of 1 kilogram. Atmospheric

pressure at sea level is 14.7 psi, or roughly 0.1 MPa.

TECHNOLOGY ASSESSMENT GAO-11-71

3.1.1.2 Maturity and

potential effectiveness

We assessed the maturity of direct air capture

of CO

with geologic sequestration at TRL

3, given that the basic principles have been

observed and reported, a system concept has

been formulated, and the literature shows proof

of concept—that is, the technology has had

laboratory demonstrations using a prototype

unit. Direct air capture of CO

is probably

decades away from commercialization, even

though its fundamental chemistry and processes

are well understood and laboratory-scale direct

air-capture demonstrations are supported at two

universities. According to the literature, direct

air capture could theoretically remove total

annual global anthropogenic CO

emissions,

estimated at approximately 33 gigatons. The

Royal Society reported that this technology had

no “obvious limit” to the amount of CO

could capture from the atmosphere. Large-scale

implementation, however, is currently neither

cost-effective nor thermodynamically efficient.

The main difficulty with direct air capture is in

the removal of atmospheric CO

in its extremely

low concentration (approximately 390 ppm),

which lowers the thermodynamic efficiency of

the process (Ranjan 2010).

This would make air

capture even more challenging than, for example,

capturing CO

from a flue stack where the

thermodynamic efficiencies were comparatively

much higher (approximately 20 percent), mainly

because of the higher concentration of CO

the flue gas (about 12 percent or approximately

120,000 ppm).

The low atmospheric CO

concentration

presents other difficulties such as a significantly

Thermodynamic efficiency refers to the ratio of the

thermodynamic minimum energy requirement to the actual

amount of energy used in the process (Zeman 2007).

large energy penalty associated with the CO

absorption system for air capture (Herzog 2003).

The total energy required to capture a unit of

from air is such that if carbon-based fuels

such as coal were used as the energy source,

more CO

would be released to the environment

than removed (Zeman 2007). The energy

process requirements for the direct air capture

of CO

would thus have to come from

noncarbon or low carbon energy sources.

Hence, substantial uncertainties surround the

scalability of air capture.

Our interviews with National Energy Technology

Laboratory (NETL) engineers revealed that

the capacity for sequestering CO

in deep

underground saline formations is vast enough

to store essentially all CO

emissions from

coal-fired power plants within the United States.

Carbon dioxide injection in subsurface geologic

formations has been used for decades in enhanced

oil recovery (EOR) to extract additional oil

from depleted oil reservoirs. EOR’s history has

made the overall challenges of the permanent

sequestration of fluids well understood. The oil

industry uses well-developed reservoir simulation

models with computer programs that have

sufficiently sophisticated computational power

to routinely characterize subsurface oil reservoirs.

It uses these tools extensively for oil production

forecasting and to predict the state of fluids in the

reservoirs, such as pressure distribution profiles

and fluid flow characteristics. Oil exploration

companies often conduct seismic surveys to

determine the size and shape of subsurface

reservoirs. They use well logging and sampling

to determine the porosity, permeability, and

resistivity of reservoirs and the hydrocarbons

Conservative estimates of the potential to store CO

emissions

geologically in North America range from 3,300 to 12,600

gigatons—that is, enough to store the CO

output of several

coal-fired power plants for many decades.

GAO-11-71 TECHNOLOGY ASSESSMENT

they contain.

Recently published reports

show that the private sector, universities, and

national laboratories are developing and using

computational techniques to model and simulate

injection, transport, and storage (CMI

2010; Grimstad et al. 2009; Hao et al. 2009;

MacMinn and Juanes 2009; Stauffer et al. 2009).

While advances in this area are notable, further

research is needed to improve the existing

technologies. What is known about CO

injection for enhanced oil recovery could help in

identifying deep underground saline formations

suitable for permanent CO

sequestration.

Carbon dioxide sequestration is being researched

for its feasibility in large-scale demonstrations.

Several worldwide projects are sequestering

in underground reservoirs to accelerate

mainstream CO

mitigation.

While the technology behind CO

injection

is well developed, an integrated direct air

capture and sequestration system has not

been demonstrated. Furthermore, geologic

sequestration of CO

has not been practiced on

the large scale envisioned by climate engineering.

Well logging is the process of measuring and recording the

rock and fluid properties of geologic formations through

drilled boreholes. It is common in the oil and gas industry for

helping to find potential reservoirs, as well for gathering

data to support geotechnical studies. Resistivity is a

characteristic electrical property of materials defined as the

electrical resistance of a conductor of unit cross-sectional

area and unit length.

The Department of Energy and NETL lead the federal

agencies in supporting carbon capture and sequestration

(CCS) research and field demonstrations. The coal-fired

Mountaineer Power Plant, run by American Electric Power

in West Virginia, has conducted a one-of-a-kind small-scale

CCS demonstration that integrated CO

capture from the flue

stack, injecting the CO

into an underground formation at the

plant site. Also, the Sleipner project, run by Statoil of Norway,

sequesters approximately 1 megaton of CO

per year in a deep

saline aquifer.

3.1.1.3 Cost factors

Cost estimates for direct air capture are based

largely on theoretical calculations or assumptions,

with some studies making qualitative cost

comparisons (Royal Society 2009). Direct air

capture’s relatively high cost results from the

extremely low concentration of CO

in the

atmosphere (about 390 ppm) compared to a

coal-fired stack (about 120,000 ppm).

Studies

have reported that the steps in selective CO

capture and release from a solvent consume

more energy—and therefore account for the

majority of the costs—than transportation and

underground sequestration. Besides the energy

costs, other factors include transportation and

logistics for sequestration of captured CO

and

the long-term management of the sequestration

site—for example, CO

injection, measuring,

monitoring, and verification.

Cost estimates for air capture in the literature

vary substantially, from a low range of $27–$135

per ton of CO

removed (Pielke 2009) to a

higher range of $420–$630 or more per ton

of CO

removed (Ranjan and Herzog 2010).

The cost estimate from Ranjan and Herzog

took thermodynamics into account, concluding

that direct air capture is unlikely to be a serious

option in the absence of a carbon market. The

literature estimates costs related to CO

injection

and monitoring of $0.20–$30 per ton of CO

sequestered, reflecting a wide range of geologic

parameters that could affect cost at specific

Direct air capture of CO

is expected to cost more than CO

capture from the flue stack of a coal-fired power plant where

concentration is substantially higher (Ranjan and Herzog

2010). Engineers from American Electric Power indicated

that the present cost of capturing CO

from a flue stack is

estimated at about $50 per ton in contrast to the likely high

cost of direct air capture.

These estimates apply only to the energy costs of the process.

Adding capital and operations costs would increase them

significantly (Ranjan 2010).

TECHNOLOGY ASSESSMENT GAO-11-71

locations (Metz et al. 2005). The potentially

high cost of direct air capture of CO

and the

lack of a carbon market could impede its

large-scale adoption.

3.1.1.4 Potential consequences

While direct air capture has minimally

undesirable consequences (except those associated

with handling process materials or chemicals),

risks have been postulated for injecting large

amounts of CO

in deep underground saline

formations (Oruganti and Bryant 2009;

Ehlig-Economides and Economides 2010).

Experience with geologic storage is limited, and

the effectiveness of risk management methods

still needs to be demonstrated for use with CO

storage. Although CO

has been injected in oil

reservoirs for decades, saline formations have

not been proven safe or permanent. Leakage

from underground sequestration sites could

contaminate groundwater or cause CO

escape into the atmosphere. One technical

paper expressing doubt about mitigation by

underground geologic CO

storage based its

theoretical analysis on established reservoir

models and assumptions of a closed form of

reservoir that would render underground geologic

storage impractical and unsuitable (Ehlig-

Economides and Economides 2010). These

assumptions and analyses were subsequently

challenged by the U.S. Department of Energy’s

(DOE) Pacific Northwest National Laboratory

(PNNL) (Dooley and Davidson 2010).

Other studies have reported that sealing faults

or fissures in an underground reservoir could

cause local pressure build-up with potential

rock fractures at the weakest point, in the

neighborhood of a fault, and cascading problems

such as well failure, CO

seepage, atmospheric

release, and groundwater contamination

(Oruganti and Bryant 2009).

Unknown or

undocumented preexisting wells in the reservoir

provide another way for CO

to escape to the

atmosphere: industry experts we interviewed

generally agreed that these concerns merit further

analysis and a thorough characterization of

geologic reservoirs.

However, studies and simulations by industry,

academia, and national laboratories suggest that

such risk is generally small and manageable. For

example, sites are chosen for sequestration only

after the thorough characterization of a reservoir

and its geology. Promising sites are assessed in

detail to ensure minimal or no risk. NETL’s

recent report advocated robust simulation to

accurately model the transport and fate of CO

for identifying, estimating, and mitigating risks

arising from CO

injection into the subsurface

formation (Sullivan et al. 2011). Thus, CO

sequestration in deep underground geologic

formations might be safe, provided the risks

were managed adequately. Our interviews

and literature review suggest that careful site

characterization and appropriate monitoring and

verification during injection are key to avoiding

hazards, steps DOE has pursued at American

Electric Power’s West Virginia plant.

3.1.2 Bioenergy with CO

capture and sequestration

3.1.2.1 What it is

Bioenergy with CO

capture and sequestration

(BECS) would harvest a biomass crop such as

switchgrass for biofuel production and capture

and sequester the CO

in geologic formations

In geology, a fault is a planar fracture or discontinuity

in a volume of rock, across which displacement has been

significant. Large faults within Earth’s crust result from the

action of tectonic forces.

GAO-11-71 TECHNOLOGY ASSESSMENT

as it is released in the conversion of biofuel to

electricity. Analogous to carbon capture and

sequestration (CCS), this leverages what is known

about bioenergy for fuels and CCS (Royal Society

2009).

As vegetation grows, photosynthesis

removes large quantities of carbon from the

atmosphere. A harvested crop could be used to

produce biofuel or simply as a fuel to generate

electricity. The CO

that would be released

could be captured and sequestered in geologic

formations. Since BECS actively absorbs CO

from the atmosphere over the entire life of a

growing plant, this approach could, on a large

scale, reduce atmospheric CO

(Read 2008).

3.1.2.2 Maturity and

potential effectiveness

We assessed the maturity of BECS at TRL 2.

Although it has been recognized that BECS can

remove CO

from the atmosphere, it has not

been applied on a scale that would affect climate

change (Carbo et al. 2010). This is an emerging

technology that leverages what is already known

about CO

capture and geologic sequestration.

For example, the Energy Research Center of

the Netherlands has a multidisciplinary research

program dedicated to BECS. BECS potentially

leads to negative CO

emissions—that is, to CO

uptake from the atmosphere through natural

sequestration of CO

in biomass (Carbo et al.

2010). Ranjan and Herzog (2010) concluded that

BECS could result in negative net emissions if the

biomass were harvested sustainably.

A variant of direct air capture, CCS captures CO

from a

fixed location such as the effluent stream of a coal-fired power

plant. The large technical and scientific literature on CCS has

brought it to the attention of government agencies, electric

power generation corporations, and the enhanced oil recovery

community (GAO 2010c; GAO 2008a). We excluded CCS

from our analysis because it is not generally considered to

involve deliberate modification of Earth’s climate system

and was therefore beyond our scope. As a forerunner of

direct air capture, CCS is a key part of the bioenergy with

sequestration (BECS) method, which, at large scale, is

considered to be climate engineering.

While the concept is simple, no instances of

BECS are in operation. For example, BECS has

not been demonstrated at any electric power

generation facility. BECS is limited by the rate

of growth of vegetation and conflicts with other

uses of land, such as agriculture. For example,

sequestering 1 gigaton of CO

through BECS

would require more than 200,000 square miles

of land for plant growth (Ranjan 2010). While

BECS could benefit local environments on a

small scale, the Royal Society views it as having a

low to medium capacity to remove CO

from the

atmosphere (Royal Society 2009; Royal Society

2001). According to the Royal Society, it can

reduce the atmospheric CO

concentration by

at most 50–150 ppm by the end of this century

compared to a projected CO

concentration of

500 ppm by 2100 (Royal Society 2009).

3.1.2.3 Cost factors and

potential consequences

BECS’s implementation costs are variable

and depend on the availability of land for

harvesting biomass, unintended emissions, the

targeted amount by which atmospheric CO

concentration would be reduced, and a carbon

market, among other things (Azar et al. 2006).

Other cost factors include transportation and

logistics for sequestration, including the long-

term management of the sequestration sites (as

with direct air capture). An article by the Energy

Research Center of the Netherlands concluded

that incremental costs for CO

capture and

storage are relatively low for biofuel production

and are competitive with carbon capture and

sequestration in fossil-fired power plants (Carbo

et al. 2010). Another study reported BECS cost

estimates of $150–$500 per ton of CO

removed

and suggested that BECS looked more promising

than air capture from a cost perspective, although

land requirements could potentially be large

TECHNOLOGY ASSESSMENT GAO-11-71

(Ranjan 2010). The literature describes BECS’s

technical feasibility and potential as a negative-

emissions energy system that is benign and

free of risks associated with some other climate

engineering approaches (Read and

Lermit 2005). As with direct air capture,

however, the CO

sequestration aspects may

pose risks. Furthermore, diverting resources to

large-scale BECS activities could pose land-use

trade-offs or affect food prices, water resources,

and fertilizer use.

3.1.3 Biochar and biomass

3.1.3.1 What it is

Biochar is a carbon-rich organic material that

results from heating biomass, or terrestrial

vegetation, in the absence of or in a limited

supply of oxygen (Whitman et al. 2010).

Biochar and biomass methods begin with the

uptake of CO

in photosynthesis (Lehmann

2007). The carbon locked in plants during their

growth would be converted to charcoal instead

of being released to the atmosphere. Biochar

differs from charcoal in that its primary use is for

biosequestration rather than fuel. That is, after

plants die, biochar can be buried underground or

stored in soil to keep carbon from being released

to the atmosphere as CO

3.1.3.2 Maturity and

potential effectiveness

We rated the maturity of biochar and biomass

at TRL 2. Ongoing and published research

is available on the sustainability of biochar to

mitigate global climate change (Woolf et al.

2010). While its proof of concept has been

Pyrolysis refers to the thermochemical decomposition of

organic material at elevated temperatures in the absence of

oxygen or where its supply is limited.

demonstrated in published modeling and

experimental results, we found uncertainties in

experimental data demonstrating the efficacy of

biochar as a net carbon sink. For example, how

long the captured CO

in biochar will remain

sequestered is uncertain. Similar to BECS,

biochar production by pyrolysis is considered

to be a carbon-negative process. Reports show

its benefits to soil, but the current immaturity

of biochar sequestration technology precludes

it from being practiced on a scale large enough

to affect the climate. Its maximum sustainable

potential for reducing net CO

, CH

, and N

emissions has been estimated at 1–2 gigatons of

–C equivalent per year, compared to annual

anthropogenic emissions of these greenhouse

gases of 15 gigatons of CO

–C equivalent

(Laird et al. 2009; Woolf et al. 2010).

Lehmann and colleagues (2006) quoted a higher

future potential of biochar as a carbon sink of

5.5–9.5 gigatons of carbon per year by 2100.

The Royal Society views biochar as low in

effectiveness because its maximum anticipated

reduction in atmospheric CO

concentration

would be only 10–50 ppm by the end of this

century compared to a projected atmospheric

concentration of 500 ppm in 2100 (Royal

Society 2009). Therefore, biochar could be

viewed as a small-scale contributor

to a climate engineering approach to enhancing

the global terrestrial carbon sink (Royal

Society 2009).

Although producing biochar and storing it in

soil have been suggested as a way to abate climate

change, provide energy, and increase crop yields,

scientists have expressed uncertainty about its

global effect and sustainability (Woolf et al.

2010). Its emission balance is highly variable and

The term CO

–C equivalent describes the extent of

global warming caused by a given type and amount of

greenhouse gas, using the functionally equivalent amount or

concentration of CO

as the reference.

GAO-11-71 TECHNOLOGY ASSESSMENT

largely depends on the feedstock available, the

existing soil fertility, and the local energy needs

(Woolf et al. 2010). While biochar and biomass

sequestration methods currently represent a trivial

carbon sink, experts are researching them as a

means of abating climate change and improving

soil fertility.

3.1.3.3 Cost factors and

potential consequences

The costs of biochar and biomass are uncertain

and inherently variable, depending on factors

such as the type of feedstock used, the cost of

pyrolysis, and carbon markets. According to one

scientist, cost might depend more significantly

on soil fertility outcomes. Roberts and colleagues

found break-even prices of about $2–$62 per

ton of CO

removed, depending on the pyrolysis

feedstock used (Roberts et al. 2010). While the

literature has reported no negative consequences

of biochar or biomass in soil, their handling

and application might pose safety and health

risks not yet adequately managed and captured

in an overall cost structure of biochar systems.

Pyrolysis could also affect health and safety.

Biochar’s effects on emissions of N

O, CH

, and

from soil are poorly characterized and need

to be further researched (Whitman et al. 2010).

Land-use trade-offs are possible (food versus

the growth of biomass for fuel), but it is unclear

whether they would be a factor for biochar. For

example, the sustainable potential for biochar

calculated by Woolf et al (2010) assumed no

land-use trade-offs.

3.1.4 Land-use management

3.1.4.1 What it is

Land-use management would enhance CO

uptake in trees, soils, and biomass to increase

their sequestration of carbon (DOE 2006).

Although it could involve a variety of activities,

we restricted our review to practices related to

forestry, including reforestation, afforestation,

and reductions in deforestation. Reforestation

would plant trees where forests were previously

cleared or burned; afforestation would plant

trees where they had not historically grown.

Reductions in deforestation would conserve

existing forests.

3.1.4.2 Maturity and

potential effectiveness

We assessed the maturity of land-use

management for climate engineering at TRL

2 because of the absence of experiments

demonstrating its effectiveness at the scale

required to affect the climate, despite the

existence of technologies and knowledge

required to sequester carbon through land-use

management for mitigation.

Bottom-up regional

studies and global top-down models yield

estimates of the potential for CO

uptake through

land-use management of 1.3–13.8 gigatons of

per year in 2030 (Nabuurs et al. 2007).

The effectiveness of land-use management

would depend on many factors, such as the

vegetation’s species, location, and growth phase.

For example, in the United States, afforestation

could potentially sequester 2.2–9.5 metric tons

of CO

per acre per year, reforestation 1.1–7.7

metric tons of CO

per acre per year, depending

on the types of trees and where they were planted

(Murray et al. 2005). Nabuurs and colleagues

China has recently accomplished afforestation on a large scale

for reasons unrelated to global climate change mitigation.

Emissions pricing can provide financial incentives for carbon

sequestration. This range of estimates of the global economic

potential of land-use management assumes a price of $100

per ton of CO

sequestered.

TECHNOLOGY ASSESSMENT GAO-11-71

reported a range for both of 0.4–14.2 tons of

per acre per year worldwide.

The rate of

carbon accumulation also varies over a tree’s

life cycle, starting out slowly when a tree is first

planted, then increasing. Although land-use

management practices are well understood and

well established, their sequestration potential

could be enhanced if scientists were to improve

the understanding of carbon uptake and transfer

in plants and soils.

The capacity for sequestration through

afforestation or reforestation also depends on

the amount of land available. The estimates of

sequestration potential reported by Nabuurs and

colleagues suggest that the land area required

to store a gigaton of CO

per year could range

from about 100,000 to 3.9 million square

miles. Other potential challenges to land-use

management for climate engineering include

threats to permanence, such as fire, insect

outbreaks, drought, or harvesting and problems

in reliably measuring, monitoring, and verifying

the amount of carbon stored, although progress

has been made in this area, and costs may decline

further as new methods are developed (Royal

Society 2009; Sohngen 2009; Canadell and

Raupach 2008; Tavoni et al. 2007; Royal Society

2001).

Climate change itself could also affect

the capacity for sequestration through land-use

management, but it is unclear whether

capacity would be enhanced or diminished

(Nabuurs et al. 2007).

Nabuurs and colleagues described trade-offs that could affect

net sequestration from land-use management. For example, a

moratorium on timber harvesting could increase the carbon

sequestered in forests but could also result in the substitution

of energy-intensive building materials, such as cement or

concrete, for wood in the construction of buildings

(Nabuurs et al. 2007).

One expert noted that natural disturbances might not

significantly challenge carbon sequestration through

land-use management in the long term.

3.1.4.3 Cost factors and

potential consequences

The costs of sequestration through land-use

management would depend on a number of

factors, most importantly the value of land

in other uses (Sohngen 2009; Jepma 2008;

Nabuurs et al. 2007; Sohngen and Sedjo 2006).

Costs would also arise from implementing and

managing forestry practices (such as planting

seedlings or harvesting); measuring, monitoring,

and verification; engaging in other transactions

(for example, developing and implementing

long-term sequestration contracts); and system-

wide adjustments (for example, changes in

the price of land) (Sohngen 2009). Although

land-use management is not generally regarded as

risky, some practices could affect other systems as

well as climate—for example, afforestation could

reduce water runoff and affect the ecology.

3.1.5 Enhanced weathering

3.1.5.1 What it is

Weathering refers to the physical or chemical

breakdown of Earth’s minerals in direct contact

with the atmosphere. Thousands of years of the

weathering of silicate rocks, for example, have

removed CO

naturally from the atmosphere, as

the CO

has reacted chemically with silicate

rocks to form solid carbonates. The reaction

can be written

CaSiO

+ CO

→ CaCO

+ SiO

This natural weathering of rocks could be

enhanced by chemically reacting the silicate or

carbonate rocks with CO

in the presence of sea

water to produce a carbonic acid solution that

GAO-11-71 TECHNOLOGY ASSESSMENT

could be spread in the ocean (Rau et al. 2007;

Royal Society 2009).

3.1.5.2 Maturity and

potential effectiveness

We assessed the maturity of enhanced weathering

at TRL 2. While the basic principles of enhanced

weathering have been observed and a concept

proposed, we did not find published experimental

results describing this approach as a CO

reducing strategy. Neither enhanced weathering’s

potential nor its technological elements have been

clarified. The chemical reaction that facilitates it

sometimes converts silicate rocks to carbonates

by reaction with CO

. The carbonate materials

resulting from enhanced weathering can be stored

in the deep ocean or in soil. Similarly, the CO

could react with carbonate rocks in seawater

for conversion and storage as bicarbonate ions

in the ocean where a large pool of such ions is

already present. Since Earth’s silicate minerals

are abundant, fixation in carbonate rocks

could remove large amounts of CO

from the

atmosphere. Scientists have made a number of

proposals to hasten natural weathering.

For

example, Rau and colleagues have reported its

potential effectiveness based on models (Rau et

al. 2007). While a very large potential for carbon

storage in soils and oceans has been reported

for this technology, its effectiveness remains

uncertain. Enhanced weathering has not been

practiced on a scale that would affect climate.

Enhanced weathering of silicate and carbonate rocks can be

represented by CaSiO

+ 2CO

+ H

O → Ca

+ 2HCO

SiO

and CaCO

+ CO

+ H

O → Ca

+ 2HCO

One proposal would spread crushed olivine, a type of silicate

rock, on agricultural and forested lands to sequester CO

and

improve soil quality (Schuiling and Krijgsman 2006). Another

proposal would cause the CO

emissions from a power plant

to react with crushed limestone (mainly calcium carbonate)

in the presence of seawater to spontaneously produce calcium

bicarbonate ions (Rau et al. 2007).

3.1.5.3 Cost factors and

potential consequences

Enhanced weathering’s costs are uncertain but are

likely to be driven by mining and transportation

costs (Royal Society 2009). Cost factors

would include, for example, the design and

implementation of a silicate-based weathering

scheme and the distribution and delivery of

raw materials. Rau and colleagues reported

variability in cost estimates of $4–$65 per ton

of CO

removed under various assumptions,

whereas IPCC’s estimate was $50–$100 per ton

of CO

captured (Rau et al. 2007; Metz et al.

2005). Overall, this technology is expected to

be relatively simple and low in cost. Enhanced

weathering that entailed large-scale mining

and transportation could require additional

energy and water and might adversely affect

air and water quality (consistent with mining

activities) and aquatic life in the long term

(Royal Society 2009). Viability would depend on

carbon markets.

3.1.6 Ocean fertilization

3.1.6.1 What it is

Ocean fertilization releases iron to certain areas

of the ocean surface to increase phytoplankton

growth and promote CO

fixation (Buesseler et

al. 2008a). Oceans act as a large sink of CO

Atmospheric CO

is exchanged at the surface

and slowly transferred to deeper waters with

the capacity to store about 35,000 gigatons of

carbon (Royal Society 2009).

Phytoplankton,

algae, and other microscopic plants on the

ocean surface absorb CO

in photosynthesis

and recycle it to the bottom as organic matter.

This represents a substantially large storage capacity compared

to the total cumulative anthropogenic carbon additions to

oceans of about 100 gigatons since preindustrial times.

TECHNOLOGY ASSESSMENT GAO-11-71

As the material settles into the deep ocean

bottom, the microorganisms residing there use

it for food, transferring CO

back to the ocean

as they breathe. The combined phytoplankton

photosynthesis at the surface and respiration

removes CO

at the surface and releases it at

greater depths. This is called the biological

pump; studies suggest manipulating this pump

to expedite CO

sequestration.

3.1.6.2 Maturity and

potential effectiveness

We assessed the maturity of ocean fertilization at

TRL 2. Basic principles have been observed and

reported, and the concept has been formulated,

with multiple studies proposing iron fertilization

as an option for reducing CO

in the atmosphere.

Oceans are the largest natural absorbers of CO

on the planet (at about 337 gigatons of CO

per year) and the largest natural reservoir of

excess carbon (Rau 2009). However, most of

the CO

the oceans absorb is released back to

the atmosphere in a continuous exchange while

only a small portion of it is transferred to and

sequestered in the deep ocean.

The large number of theoretical studies

attempting to understand fertilization’s

complexities with sophisticated ocean models—as

many as 12 between 1993 and 2008—have been

complemented with only a few small-scale field

experiments, whose results were uncertain and

not well documented. Ocean fertilization studies

suggest that 30,000–110,000 tons of carbon

could be sequestered from air by adding 1 ton of

iron to certain parts of the ocean, but verifying

this technology’s effectiveness is difficult and

uncertain (Buesseler et al. 2008b).

For example,

modeling simulations suggest a cumulative

One ton of carbon corresponds to 3.67 tons of CO

storage potential of 26–70 gigatons of carbon

(equivalent to 95–255 gigatons of CO

) for

large-scale ocean fertilization—relatively low

compared to terrestrial sequestration potential in

vegetation (200 gigatons of carbon) or in deep

geological formation (several hundred gigatons of

carbon) (Bertram 2009).

Another study based on models reported

that large-scale sustained iron fertilization

(30 percent of the global ocean area) could store

at most 0.5 gigatons of carbon (equivalent to

about 2 gigatons of CO

) per year. This amount

is small compared to anthropogenic emissions

of approximately 8–9 gigatons of carbon

(equivalent to about 30–33 gigatons of CO

)

per year. According to the Royal Society, ocean

fertilization could reduce the atmospheric CO

concentration by a maximum of 10–30 ppm

by the end of this century, which would be

considered to be low in effectiveness. While

these estimates have not been substantiated

experimentally, these studies show that even

sustained fertilization of oceans would have only

a minor effect on the increasing atmospheric CO

concentration (Secretariat of the Convention on

Biological Diversity 2009).

Ocean fertilization as a long-term carbon storage

strategy has not been demonstrated (Buesseler

et al. 2008b). The literature characterizes its

effectiveness as highly uncertain, the models

governing biochemical cycling of nutrients

and the circulation of ocean currents as poorly

understood or uncertain, and the strategy for

mitigating CO

as risky. For example, the science

is unclear regarding ecological consequences, the

duration of carbon sequestered in the oceans, and

the frequency with which iron should be added

(Buesseler et al. 2008b). Scientists are researching

the ocean’s biochemical processes and the

effects and efficacy of iron fertilization to better

understand them.

GAO-11-71 TECHNOLOGY ASSESSMENT

3.1.6.3 Cost factors and

potential consequences

Ocean fertilization could be cost-effective

at capturing and sequestering atmospheric

in the deep ocean, but relatively little

is known about its efficacy.

The design and

implementation of any ocean fertilization scheme,

including mining, distribution, and delivery of

materials, would affect its success. The literature

has reported significant uncertainty with respect

to cost. Some ocean fertilization modeling has

helped determine its efficiency at removing

carbon from the atmosphere but estimating a cost

range is difficult. One estimate put the minimum

cost at approximately $8 per ton of CO

removed

(Buesseler et al. 2008b). An evaluation by Boyd

characterized ocean fertilization as a medium-risk

strategy with costs of $8–$80 per ton of CO

removed (Boyd 2008).

Because ocean fertilization is not well understood

and is largely theoretical, it could pose ecological

risks (Royal Society 2009). A report from the

Woods Hole Oceanographic Institution indicated

that iron-fertilized phytoplankton blooms could

eventually prevent oceans from sustaining life.

An image in that report showed bloom and

anoxic (or dead) zones stretching for hundreds

of kilometers (Buesseler et al. 2008b).

The

Royal Society and the U.K. House of Commons

Science and Technology Committee reported

that ecosystem-based methods—whether

fertilizing the ocean or blocking sunlight—would

be subject to unknown risks if implemented on

a large scale. Other studies have also presented

images of the unintended consequences of

Despite the fact that oceans exchange large quantities of CO

with the atmosphere in a natural process, comparatively little

is known about sequestering CO

by ocean fertilization.

Anoxia means the absence of oxygen. Algal blooms in the

ocean can deplete available oxygen in the water, leading to

dead or anoxic zones.

manipulating ecosystems—dead zones in the

sea resulting from phytoplankton boom are an

example (Buesseler et al. 2008b). Other potential

risks of ocean fertilization are greater ocean

acidification, additional emissions of greenhouse

gases, and the reduction of oxygen in the ocean to

levels some species cannot tolerate (Buesseler

et al. 2008b).

3.2 Selected SRM Technologies

In this section, we summarize our assessment

of the maturity of selected SRM technologies

and present information from peer-reviewed

literature on their potential effectiveness, cost

factors, and potential consequences. TRL

ratings indicate the maturity of each technology.

Potential effectiveness is described in terms of

the anticipated ability to counteract warming

caused by doubling the preindustrial atmospheric

concentration of CO

. In calculating our ratings,

we relied on reported results from

• climate engineering modeling studies using

general circulation models (GCM) and

• energy balance studies of the effects of

increasing reflectivities.

Cost factors represent resources required to

counteract global warming from doubling the

preindustrial atmospheric concentration of CO

or, for technologies that are not anticipated

to be fully effective, the resources required to

counteract warming to the maximum extent

possible. Potential consequences associated

with each technology include reported negative

consequences and cobenefits. (See table 3.2.)

TECHNOLOGY ASSESSMENT GAO-11-71

Technology Maturity

Potential

effectiveness

Cost factors

Potential

consequences

Stratospheric

aerosols

Low (TRL 1):

• Basic principles

understood and

reported

• No system concept

proposed

Potentially fully

effective:

• Aerosols must

be continuously

replaced

• Design, fabrication, testing,

acquisition, and deployment of

aerosol delivery scheme, including

distribution and delivery

mechanisms, fabrication of aerosol

dispersal equipment, and all

associated infrastructure

• Literature-based estimates vary

significantly: $35 billion to $65

billion in the first year; $13 billion

to $25 billion in operating cost

each year thereafter

• Little change in global average

annual precipitation

• Disruption of Asian and

African summer monsoons

with accompanying reduction

in precipitation

• Delayed ozone layer recovery in

southern hemisphere and about

a 30-year delay in recovery of

Antarctic ozone hole

• Scattering interference with

terrestrial astronomy

• Efficiency of solar-collector

power plants reduced by

increased diffuse radiation

Marine cloud

brightening

Low (TRL 2):

• Basic principles

understood and

reported

• System concept

proposed

• Proof of concept not

demonstrated

Potentially fully

effective:

• Model-dependent

estimates of

effectiveness vary

• Clouds must be

continuously

brightened

• Design, fabrication, testing,

acquisition, and deployment of a

fleet of 1,500 wind-driven spray

vessels

• Fleet infrastructure and operation

• Estimates in the scientific

literature vary significantly at $42

million for development, $47

million for production tooling,

$2.3 billion to $4.7 billion for

1,500-vessel fleet acquisition

• Small changes in global

average temperature, regional

temperatures, and global

precipitation

• Large regional changes in

precipitation, evaporation, and

runoff; both precipitation and

runoff increase, and the net

result might not “dry out” the

continents

Table 3.2 Selected SRM technologies, continues on next page

GAO-11-71 TECHNOLOGY ASSESSMENT

Technology Maturity

Potential

effectiveness

Cost factors

Potential

consequences

Scatterers or

reflectors in

space

• Earth orbit

• Deep space

Low (TRL 2):

• Basic principles

understood and

reported

• System concepts

proposed, but proof

of concept not

demonstrated

Potentially fully

effective:

• Spacecraft’s limited

lifetime

• Design, fabrication, testing,

acquisition, and deployment of

a fleet of millions to trillions of

reflecting or scattering spacecraft

• Launch vehicle

• Infrastructure and operation

• Estimates in the scientific

literature vary significantly: an

estimate of $1.3 trillion and an

estimate of less than $5 trillion

Earth-orbit technologies:

• A cool band in the tropics

with unknown effects on

ocean currents, temperature,

precipitation, and wind

• A multitude of bright “stars” in

the morning and evening that

would interfere with terrestrial

astronomy

Deep-space technologies:

• Annual average tropical

temperatures a little cooler

• Annual average higher latitude

temperatures a little warmer

• Small reduction of annual

global precipitation

Terrestrial

reflectivity

• Deserts

• Flora

• Urban or

settled areas

Low (Up to TRL 2):

• Basic principles

understood and

reported

• One technology

proposed a system

concept but without

demonstrated proof of

concept

Potential

effectiveness of 0.21

(urban areas) to

more than

57 percent (deserts)

• Sustainability

issues: maintaining

reflectivity and

missing information

on reflective flora

• Design, fabrication, testing,

acquisition, and deployment of

reflective material or flora

• Infrastructure and maintenance

• Estimates in the scientific

literature to maintain reflectivity

vary greatly from $78 billion

(urban areas) to $3 trillion per

year (deserts)

• Cool deserts might change

large-scale patterns of

atmospheric circulation

• Reflective crops would

probably not significantly affect

global average temperature but

might reduce regional summer

temperatures

• Reflective urban areas would

probably not affect global

average temperature but might

reduce air-conditioning costs

Table 3.2 Selected SRM technologies: Their maturity and a summary of available information. Source: GAO.

a standard tool that some federal agencies use to assess the maturity of emerging technologies. We characterized technologies with TRL scores lower than 6 as “immature” (see section 8.1). The TRL rating

methodology considers the maturity level of the whole integrated system rather than individual components of a particular technology.

We assessed potential effectiveness in terms of a technology’s potential ability to counteract global warming caused by doubling the preindustrial CO

concentration.

Cost factors are resources a system uses to counteract global warming caused by doubled preindustrial atmospheric CO

concentration, or for technologies that are potentially not fully effective, resources

required to counteract global warming to the maximum extent possible. Some of the studies we reviewed indicate possible cost levels, which we provide here for illustration. We did not evaluate this

information independently.

Includes potential consequences, risks, and cobenefits.

TECHNOLOGY ASSESSMENT GAO-11-71

3.2.1 Stratospheric aerosols

3.2.1.1 What it is

Deploying aerosols would use knowledge gained

from volcanic eruptions that inject aerosols

into the stratosphere, cooling Earth for short

periods. Aerosols smaller than 1 micrometer in

diameter (1 millionth of a meter) would cool

Earth primarily by scattering a fraction of the

solar radiation. While enough solar radiation

would be scattered back into space to cool Earth,

a larger fraction would be scattered toward Earth,

increasing diffuse radiation (Robock 2000).

Larger aerosols would scatter solar radiation less

efficiently and absorb both solar and thermal

radiation, acting somewhat like a greenhouse

gas (Rasch, Crutzen, and Coleman 2008; Rasch,

Tilmes et al. 2008). If the volcanic sulfate aerosols

were sufficient to cool Earth, the sulfates would

accumulate in size and remain in the stratosphere

for about 1 year.

3.2.1.2 Maturity and

potential effectiveness

We assessed stratospheric aerosol technology at

TRL 1 because only basic principles have been

reported. We could not rate this technology at

TRL 2 because we found no system concepts

reported in the literature. Recent estimates using

complex coupled atmosphere-ocean general

circulation models indicated that about 3

million tons of sulfur injected per year into the

stratosphere and forming volcanic-sized sulfate

aerosols would compensate for the doubled CO

concentration (Rasch, Crutzen, and Coleman

2008). In a recent investigation using a chemistry

While the published research has focused on sulfate aerosols

(Royal Society 2009), other aerosols such as alumina (Teller

et al. 1997) and self-levitated nanoparticles (Keith 2010) have

also been considered.

climate model, Heckendorn and colleagues found

that sulfates from continuous injection of sulfur

gas formed larger aerosols that would be less

effective than volcanic sized aerosols (Heckendorn

et al. 2009). Because sulfate aerosols have a

lifetime of about a year in the stratosphere, they

must be replenished to sustain their cooling effect

(Rasch, Crutzen, and Coleman 2008).

3.2.1.3 Cost factors and

potential consequences

It could cost $35 billion to $65 billion in the

first year and $13 billion to $25 billion in

each subsequent year to inject sufficient sulfate

aerosols into the stratosphere to counteract global

warming caused by doubling preindustrial CO

concentration. Robock and colleagues estimated

the cost of injecting 1 million tons of a sulfur

gas (that will become sulfate aerosols) per year

into the stratosphere (Robock et al. 2009). Since

about 3 million tons of sulfur might be required

to counteract global warming caused by doubling

preindustrial CO

concentration, we scaled

Robock and colleagues’ cost estimate, assuming

no economy of scale, to 3.2 million

and 6 million tons per year of hydrogen sulfide

and sulfur dioxide, respectively (gases containing

3 million tons of sulfur). The scaled cost estimate

is $35 billion to $65 billion in the first year (the

cost of the airplanes used to inject the aerosols

plus 1 year of operations) and $13 billion to

$25 billion in operating costs in each subsequent

year to sustain the effort. Robock and colleagues

considered several potential aerosol injection

systems, including KC-135 aircraft-refueling

tankers and F-15 aircraft. They found that

the total cost of using the aircraft-refueling

tankers would be lower than the total cost of

the alternatives, but the tankers do not fly high

enough (Robock et al. 2009).

GAO-11-71 TECHNOLOGY ASSESSMENT

Using the F-15s was the least expensive among

the remaining alternatives. Robock and

colleagues’ estimated operating cost for the

F-15s was an upper bound based on the hourly

cost of the tankers; the authors expected that

the hourly cost of operating F-15s would be

lower because they use less fuel and fewer pilots

than the tankers. However, because the F-15s

are smaller than the tankers, they would require

more than ten times the number of trips that the

tankers would require to inject the same quantity

of aerosols. Other alternatives considered by

the authors, including injection systems based

on artillery or balloons, would be significantly

more expensive than the fighter aircraft. The

scaled estimates do not include system design,

fabricating aerosol dispersal equipment, or

infrastructure.

Volcanic stratospheric sulfate aerosols increase

diffuse solar radiation, which can increase the

growth of terrestrial vegetation (Robock et al.

2009). Cooling by these aerosols can interfere

with the hydrological cycle (Trenberth and Dai

2007). The surface area of these aerosols can

lead to reactions that deplete stratospheric ozone

(Tilmes et al. 2008; Solomon 1999). Robock and

colleagues reported performing a modeling study

using an IPCC “business-as-usual” scenario with

an increase in greenhouse gases and sufficient

stratospheric sulfate aerosols to significantly cool

Earth. They found little annual average change

in global precipitation but significantly reduced

precipitation in India, with large reductions in

summer monsoon precipitation in India and

northern China that could threaten food and

water supplies. They found a similar reduction in

the Sahel in Africa. They also found that abruptly

stopping the injection of aerosols would raise

temperature rapidly and be difficult to adapt to.

In another modeling study using the same

greenhouse gas scenario, Tilmes and colleagues

found that changes in stratospheric dynamics

and chemistry delayed the recovery of the ozone

layer in middle and high latitudes in the southern

hemisphere and reduced the ozone layer in high

latitudes in the northern hemisphere (Tilmes et

al. 2009). The recovery of the Antarctic ozone

hole would be delayed by about 30 years.

They stated that the increase in ultraviolet

radiation of up to 10 percent observed in the

middle and high latitudes in the 1980s and 1990s

would probably worsen.

Using an aerosol-chemistry climate model,

Heckendorn and colleagues found larger

sulfate aerosols, which increased stratospheric

water vapor and reduced stratospheric ozone

(Heckendorn et al. 2009). Additional water vapor

(a greenhouse gas) would reduce effectiveness but

reduced ozone (another greenhouse gas) would

increase effectiveness. The net effect is not known

because detailed radiation forcing calculations

were beyond the scope of the 2009 study.

Other collateral consequences of stratospheric

aerosols would include negative effects on

astronomy and on solar energy power plants.

Suspended above all terrestrial telescopes,

stratospheric aerosols would interfere with

terrestrial optical astronomy. Scattering from

stratospheric aerosols would also reduce the

efficiency of power plants that concentrate solar

radiation to generate electricity. Although solar

radiation scattered from aerosols would result in

significant diffuse radiation, the concentrators in

these power plants cannot use it. For example,

the peak power output of Solar Electric

Generating Stations in California fell up to

20 percent after Mount Pinatubo erupted, even

though total solar radiation was reduced by less

than 3 percent (Murphy 2009). Aerosol effects

in the stratosphere could be reversed by stopping

their injection because sulfate aerosols remain in

the stratosphere for approximately 1 year.

TECHNOLOGY ASSESSMENT GAO-11-71

3.2.2 Cloud brightening

3.2.2.1 What it is

Reflectivity in clouds generally increases as the

number of water droplets in them increases

(Twomey 1977). Latham and colleagues

proposed to increase the reflectivity of marine

clouds by increasing the number of water droplets

(Latham et al. 2008). They proposed to loft

droplets of sea water micrometers in diameter

that would shrink by evaporation as they rose

into the base of the clouds, where moisture

would condense, and increase their number

(Latham et al. 2008). In designing wind-driven

spray vessel-based cloud brightening equipment,

Salter, Sortino, and Latham (2008) proposed to

avoid the problems of remotely operating and

maintaining sails, ropes, and reefing gear by

using Flettner rotors—vertical spinning cylinders

that produce forces perpendicular to the wind

direction—instead of sails.

3.2.2.2 Maturity and

potential effectiveness

We assessed cloud brightening technology at

TRL 2. Basic principles have been reported,

allowing at least TRL 1. Demonstration of

proof of concept has not been reported (Salter,

Sortino, and Latham 2008), ruling out TRL 3.

A system concept has been proposed, and there

is encouraging evidence that this technology

might work: Ship tracks (which are white streaks

observed in satellite images of the oceans that are

attributed to sulfate aerosols in the exhaust trails

from ships) indicate that adding aerosols to the

marine environment can make clouds, but they

fall short of proof of concept that lofting droplets

of sea water into marine clouds will brighten

them as assumed in the analyses discussed below.

Having a system concept does not automatically

qualify this technology for TRL 2 but it cannot

be ruled out, given the information available in

Salter, Sortino, and Latham (2008).

Four recent investigations of cloud brightening

reported effectiveness ranging from fully effective

to fully effective with a significant margin.

Latham and colleagues used two different

atmosphere-only general circulation models and

calculated the increased reflectivity of brightened

clouds. They found full effectiveness with

significant margin for one when they brightened

all marine clouds and full effectiveness for the

other when they brightened clouds over 35 to

45 percent of the ocean area (Latham et al. 2008).

Using analytical methods, Lenton and Vaughan

found full effectiveness but warned that

conversion of droplets reaching the base of the

clouds into droplets in the clouds is not well

understood and, if the conversion is insufficient,

this technology would not be effective (Lenton

and Vaughan 2009). Rasch and colleagues

used a fully coupled atmosphere-ocean general

circulation model and found full effectiveness if

clouds were brightened over between 40 percent

and 70 percent of the oceans (Rasch et al. 2009).

Bala and colleagues used a similar atmosphere

model coupled to a simple slab-ocean/sea-ice

general circulation model and found full

effectiveness when they reduced water droplet size

in all marine clouds (Bala et al. 2010). Brightened

clouds have a lifetime of a few days and must

be continuously brightened to sustain cooling

(Latham et al. 2008).

3.2.2.3 Cost factors and

potential consequences

It could cost $2.4 billion to $4.8 billion to

brighten enough marine clouds to compensate

for a doubling of the concentration of CO

in the

atmosphere. Salter, Sortino, and Latham (2008)

estimated that full effectiveness would require a

GAO-11-71 TECHNOLOGY ASSESSMENT

fleet of 1,500 of their wind-driven spray vessels.

Their cost estimate did not include system

testing, acquisition, deployment, infrastructure,

and operation.

The investigations using coupled atmosphere-

ocean general circulation models predicted

climate changes. Rasch, Latham, and Chen

(2009), using a fully coupled ocean-atmosphere

model, found that as they brightened increasing

fractions of clouds, they not only could

counteract global warming caused by doubling

atmospheric CO

concentrations but could also

counteract the effects of this warming on sea ice

and precipitation—but not all at the same time.

For example, when they counteracted global

warming, they overcompensated for the loss

of south polar sea ice and the change in global

precipitation and undercompensated for the loss

of north polar sea ice (Rasch, Latham, and Chen

2009). Bala and colleagues used an atmosphere

coupled to a simple slab-ocean/sea-ice model and

found that

• changes in global and regional annual average

temperatures were small,

• changes in global annual precipitation were

small, and

• regional changes in precipitation, evaporation,

and runoff were large. Precipitation and runoff

increased over land, particularly over Central

America, the Amazon, India, and the Sahel,

suggesting that this technology might not dry

the continents (Bala et al. 2010).

The total rough cost estimate for the cloud brightening

system would be $2.4 billion to $4.8 billion. This cost

estimate is made up of Salter, Sortino, and Latham’s estimates

of $3.1 million for the first 2 years of engineering;

$39 million for the next 3 years for final design, including

construction of a prototype; $47 million for production

tooling; and production costs of $2.3 billion to $4.7 billion

($1.56 million to $3.13 million each) for 1,500 45-meter,

300-ton wind-driven spray vessels (Salter et al. 2008).

The brightness of clouds could be returned to

normal within a few days of ceasing to

deploy the cloud brightening technology

(Latham et al. 2008).

3.2.3 Scatterers or reflectors in space

3.2.3.1 What it is

Proposals have been made to reduce the solar

radiation that reaches Earth by placing scatterers

or reflectors in Earth orbit or in deeper space at a

stable position between Earth and the Sun

called the inner Lagrange point (or L1)—

approximately 1 percent of the distance from

Earth toward the Sun—where gravitational and

orbital forces are balanced.

Proposed technologies include scatterers or

reflectors in Earth orbit. NAS dismissed the

use of 55,000 110-ton 100-square kilometer

reflective solar “sails” in orbit that would reflect

1 percent of solar radiation as “a very difficult if

not unmanageable control problem”

(NAS 1992).

Pearson, Oldson, and Levin (2006) proposed

Saturn-like rings of space dust or parasol

spacecraft. To be practical, the space dust option

would require the ability to fabricate in space.

The ring of spacecraft would consist of 5 million

parasol spacecraft, each measuring 5 km long

by 200 m wide (1 square km) and having mass

of 1,000 kg. They would be electromagnetically

tethered in Earth’s equatorial plane at altitudes

between 1,300 km and 3,200 km. The

spacecraft’s parasols would point at the Sun and

shade the tropics of the winter hemisphere.

In 1992, reflecting 1 percent of solar radiation was thought

to counteract the global warming from doubling the

concentration of CO

in the atmosphere (NAS 1992).

Up-to-date modeling studies indicate that reflection of about

1.8 percent is required (Govindasamy and Caldeira 2000;

Govindasamy et al. 2002; Caldeira and Wood 2008).

TECHNOLOGY ASSESSMENT GAO-11-71

The proposed options also included scatterers or

reflectors at L1:

• a 3,400-ton, 1,800-km diameter diaphanous

scattering screen fabricated in low Earth orbit

(Teller et al. 1997);

• a 100-million ton, 2,000-km diameter,

10 micrometer thick opaque disc or transparent

prism made from moon glass (Early 1989);

• a 420-million ton, 3,600-km diameter,

5.1 micrometer thick iron mirror made

from asteroids (McInnes 2002);

• 16 trillion spacecraft (a total of 19 million

tons), each 0.6 meters in diameter and

5 micrometers thick, covering an ellipse

6,200 km by 7,200 km (Angel 2006).

The first three technologies are impractical at

this time because they require manufacturing

capabilities in space. The fourth technology

would consist of 16 trillion autonomous

fliers, manufactured on Earth, launched

electromagnetically into orbit, and moved into

position with ion propulsion. Once in position,

they would use a system analogous to the global

positioning system and radiation pressure motive

power with tilting mirrors for station-keeping.

3.2.3.2 Maturity and

potential effectiveness

We assessed scattering or reflecting technologies

in space at TRL 2. Basic principles have

been reported and system concepts have

been proposed, allowing at least TRL 1, but

demonstration of proofs of concept have not

been reported (Angel 2006; Pearson et al. 2006),

ruling out TRL 3. Having system concepts does

not automatically qualify these technologies for

TRL 2 but it cannot be ruled out, given the

information available in Angel (2006) and in

Pearson, Oldson, and Levin (2006).

Pearson, Oldson, and Levin (2006) used a

simplified one-dimensional energy balance

model to design a system of parasol spacecraft

to reduce solar radiation to compensate for

doubled preindustrial CO

concentrations in the

atmosphere. Their design study indicated that

this could be accomplished by shading about

36 percent of a Saturn-like equatorial ring with

their parasol spacecraft.

Angel’s autonomous spacecraft fliers were

designed to reduce solar radiation by the

1.8 percent required by general circulation

models (in this case, an atmospheric general

circulation model coupled to slab ocean and

sea-ice models) (Govindasamy and Caldeira

2000) to compensate for global warming caused

by doubling the preindustrial CO

concentration.

None of these space-based SRM technologies

would be a realistic contributor in the short

term. They should not be dismissed from future

consideration, particularly if climate engineering

were to be employed for as long as a century

(Royal Society 2009). However, the spacecraft

would have to be replaced when they reached the

end of their service life to sustain cooling.

3.2.3.3 Cost factors and

potential consequences

Following NAS’s assertion that the cost of

establishing space-based climate engineering

projects would be dominated by launch costs

(NAS 1992), Pearson, Oldson, and Levin

(2006) estimated a cost of $1.3 trillion for their

equatorial Saturn-ring-like collection of reflectors.

Their launch cost was based on a proposed ram

accelerator and an orbiting tether, achieving a

low Earth orbit launch cost of $250 per kg. This

GAO-11-71 TECHNOLOGY ASSESSMENT

cost estimate did not include design, fabrication,

testing, acquisition, deployment, infrastructure,

or operation. They did not provide an explicit

projected lifetime for their spacecraft. However,

they did explore the consequences of a 100-year

lifetime. Following on their launch costs as

discussed, the replacement cost estimate would

be $13 billion per year.

It could cost less than $5 trillion for Angel’s

fliers at L1. Fabrication costs were estimated at

$50 per kg, which Angel rounded up to

$1 trillion. Estimates of launch costs were based

on 20 electromagnetic launchers each launching

800,000 fliers into orbit every 5 minutes for

10 years. The electromagnetic launchers would

put the fliers into orbit, and ion propulsion

would move them to L1, where the fliers would

use mirrors to adjust radiation pressure from

solar radiation to maintain position. The cost

estimate for the launchers was $600 billion and

the estimated cost of electrical energy for the

launchers was $150 billion; Angel rounded the

sum to $1 trillion, corresponding to a launch cost

of $50 per kg. Angel stated that a total project

cost, including development and operations, of

less than $5 trillion seemed possible but gave

insufficient detail to evaluate development

and operation costs. Also, he did not explicitly

mention testing, acquisition, deployment, and

infrastructure. The projected lifetime for the

fliers is 50 years, which means that 320 billion

fliers would have to be replaced every year, but

Angel did not provide an estimated cost for

replacement.

Orbital equatorial Saturn-ring-like disposition

of reflectors is a regional technology that would

shade and cool the winter portion of the tropics.

The design study used a simplified energy balance

model of Earth’s climate system, not a general

circulation model (GCM). Therefore, climate

responses other than a set of average temperatures

for bands of latitudes are not available. The

effects on the ocean currents, ocean temperature,

precipitation, and wind are unknown. However,

a multitude of bright “stars” at morning

and evening would interfere with terrestrial

astronomy.

Uniformly reducing solar radiation with reflectors

or scatterers at L1 enough to counteract the

warming effect of doubling the concentration

of CO

might not significantly reduce CO

fertilization from doubling CO

. Govindasamy

and colleagues modeled this effect with normal

and uniformly reduced solar radiation at both

the concentration of CO

in 1991 and double

the concentration of CO

in 1991 (Govindasamy

et al. 2002). In their modeling study, they chose

a reduction in solar radiation that could nearly

counteract the warming effect of doubling the

concentration of CO

. They found that doubling

resulted in CO

fertilization—that is, plant

productivity increased by 76–77 percent and

biomass increased by 87–92 percent.

When they

uniformly reduced solar radiation to counteract

the warming effect of this doubling of the

concentration of CO

, they found that plant

productivity fell by 2.3–3 percent and biomass

fell by 1.9–4.7 percent. Govindasamy and

colleagues indicated that in reality, CO

-fertilized

ecosystems might encounter nutrient limitations,

diminishing the magnitude but not changing the

direction of the CO

fertilization. Furthermore,

they indicated that CO

fertilization might affect

ecosystems in ways not represented in the model

through species abundance and competition,

habitat loss, biodiversity, and other disturbances.

This investigation applies directly to reflectors

or scatterers at L1 that uniformly reduce solar

radiation without otherwise affecting the Earth

system. Therefore, this modeling study indicated

In this context, plant productivity is net primary productivity,

which is net carbon uptake by vegetation.

TECHNOLOGY ASSESSMENT GAO-11-71

that CO

fertilization would outweigh reduction

in plant productivity because of uniformly

reduced solar radiation from reflectors or

scatterers at L1.

Modeling studies indicate that SRM technologies

that counteract the greenhouse effect of a

doubled preindustrial concentration of CO

uniformly reducing solar radiation also indicate

that the globally averaged engineered climate is

very similar to the globally averaged preindustrial

climate (Caldeira and Wood 2008; Govindasamy

et al. 2002; Govindasamy and Caldeira 2000).

These studies indicated that annual average

tropical temperatures would be a little cooler,

the higher latitudes might be a little warmer,

and the reduction of annual global precipitation

would be small.

Since the spacecraft in Earth orbit and at L1

would be controlled, it should be possible to

reverse these technologies. It is assumed that

parasol spacecraft in Earth orbit, which are

controlled to maximize shading, could be reversed

by commanding the parasols to minimize shading

(Pearson et al. 2006). Fliers at L1 could be

reversed by commanding the fliers to go into

halo orbits (Angel 2006).

3.2.4 Reflective deserts,

flora, and habitats

3.2.4.1 What it is

Increasing Earth’s surface reflectivity in deserts,

flora, and settled areas has been proposed.

Gaskill would double the reflectivity of deserts

by covering them with white polyethylene,

estimating that up to 12 trillion square meters

of Earth’s deserts (about 2 percent of Earth’s

surface) would be suitable for reflectivity

enhancement (Gaskill 2004; Gaskill n.d.).

Similarly, Ridgwell and colleagues proposed

increasing the reflectivity of crops by selecting

varieties that are glossy or have reflective shapes

and structure (Ridgwell et al. 2009). Hamwey

proposed to increase the reflectivity of open

shrubland, grasslands, and savannah and to

double the reflectivity of all human

settlements, excluding agricultural land

(Hamwey 2007). Akbari, Menon, and

Rosenfeld (2009) proposed to increase the

reflectivity of urban roofs and pavement.

3.2.4.2 Maturity and

potential effectiveness

We assessed increased reflectivity of desert

technology at TRL 2. Basic principles have been

reported and a system concept has been proposed,

allowing at least TRL 1, but demonstration of

proof of concept has not been reported (Gaskill

2004; Gaskill n.d.), ruling out TRL 3. Having

a system concept does not automatically qualify

this technology for TRL 2 but it cannot be

ruled out given the information available in

Gaskill (2004) and Gaskill (n.d.). We assessed

technologies for increasing the reflectivity of

flora and settled areas at TRL 1 because only

basic principles have been reported; the absence

of system concepts precluded a rating of TRL 2

(Ridgwell et al. 2009; Hamwey 2007).

Technologies for increasing the reflectivity of

deserts could potentially be more than 57 percent

effective in compensating for global warming

from doubled preindustrial CO

. Gaskill

proposed to increase reflectivity from 36 to

80 percent over 10 trillion square meters of the

12 trillion square meters of desert areas

that he deemed suitable (Gaskill 2004; Gaskill

n.d.). The Royal Society’s (2009) and Lenton

and Vaughan’s (2009) interpretation of

Gaskill corresponded to an effectiveness of

74 percent. Lenton and Vaughan’s refinement

GAO-11-71 TECHNOLOGY ASSESSMENT

of Gaskill’s proposal corresponded to 57 percent

effectiveness, accounting for lower average

intensity of solar radiation over land and

absorption in the atmosphere. However, they also

stated that deserts have higher-than-average solar

radiation because they are generally in the lower

latitudes, so that increased reflectivity would be

somewhat more effective (Lenton and

Vaughan 2009). Sustaining reflective deserts

would require maintenance.

Increasing the reflectivity of flora could be up

to about 25 percent effective. Ridgwell and

colleagues investigated the effect of increasing the

reflectivity of crops with a fully coupled climate

model (Ridgwell et al. 2009). They focused on an

increase of 20 percent, asserting that an increase

of 35 percent observed after coating plants with

a white chalky suspension provided a first-order

guide as to the possible upper limit of reflectivity

increase. They found a global average cooling of

only 0.11 degrees Celsius. Hamwey investigated

increasing the reflectivity of open shrubland,

grasslands, and savannah with a static two-

dimensional radiative transfer model (Hamwey

2007). His preliminary estimate was that an

increase in reflectance of 25 percent corresponded

to about 16 percent effectiveness. Lenton and

Vaughan interpreted these results with energy

balance analyses (Lenton and Vaughan 2009).

Following Ridgwell and colleagues, their

estimate—using a larger area estimate and a

40 percent increase in reflectance—corresponded

to an upper limit of about 9 percent effectiveness.

Their interpretation of Hamwey’s data

corresponded to essentially the same effectiveness

as Hamwey’s—about 16 percent. Thus the total

effectiveness of reflective flora—cropland, open

shrubland, grasslands, and savannah combined,

using Lenton and Vaughan’s reinterpretations

based on energy balance—would be up to about

25 percent.

Because crops are customarily replanted

annually, no additional effort should be required

to maintain their reflectivity (Ridgwell et al.

2009). Hamwey provided no information on

the effort required to maintain the reflectivity of

open shrubland, grasslands, and savannah

(Hamwey 2007).

Increasing the reflectivity of settled areas could

be about 4.3 percent effective. Akbari, Menon,

and Rosenfeld’s (2009) estimate for urban area

equal to 1 percent of Earth’s land surface and a

net increase for urban reflectivity by 10 percent

corresponded to an effectiveness of only about

1.2 percent. However, Lenton and Vaughan

(2009) suggested that the urban area Akbari,

Menon, and Rosenfeld (2009) used, could have

been 5.6 times overestimated, in which case

increasing the reflectivity of urban areas would

be only about 0.21 percent effective. Hamwey’s

(2007) estimate for doubling reflectivity for areas

of human settlement (not including agricultural

land) corresponded to an estimated overall

effectiveness of about 4.6 percent. Lenton and

Vaughan’s correction to Hamwey’s estimate

accounting for absorption in the atmosphere and

an underestimate in solar radiation corresponded

to an effectiveness of about 4.3 percent.

Maintaining high reflectivity would be the

sustainability issue for these technologies.

3.2.4.3 Cost factors and

potential consequences

The maintenance cost for reflective deserts that

could potentially compensate for more than

57 percent of the doubling of the concentration

of CO

in the atmosphere could be about

$3 trillion per year. Gaskill proposed to increase

reflectivity of 10 trillion square meters of the

deserts (Lenton and Vaughan 2009; Royal

Society 2009). The Royal Society provided the

following cost estimate for reflective deserts

TECHNOLOGY ASSESSMENT GAO-11-71

(Royal Society 2009): if the cost of reflective

sheeting, with an allowance for routine

replacement from damage, were somewhat

similar to that of painting, it would be several

trillion dollars per year. The Royal Society’s

method would yield an annual maintenance

cost for reflective deserts of about $3 trillion

(Royal Society 2009). The estimates did not

include design, fabrication, testing, acquisition,

installation, or infrastructure costs.

We found no cost estimates for increasing the

reflectivity of flora in the peer-reviewed literature

(Royal Society 2009). We found no cost

estimates for increasing the reflectivity of areas of

human settlement in the peer-reviewed literature.

However, the estimated maintenance cost for

urban areas that would compensate for 0.21 to

1.2 percent of the doubled concentration of

in the atmosphere was from about

$78 billion to about $440 billion per year. The

Royal Society (2009) made a rough estimate of

the costs of painting urban surfaces and structures

white using standard costs for domestic and

industrial painting. Assuming repainting once

every 10 years, it estimated combined paint and

manpower costs on the order of $0.30 per square

meter per year. The urban area Akbari, Menon,

and Rosenfeld (2009) studied was 1 percent of

Earth’s land area—that is, about 1.47 trillion

square meters. Using the Royal Society’s (2009)

cost estimation method, maintenance would cost

about $440 billion per year. Lenton and Vaughan

(2009) suggested that the global urban area might

be only about 260 billion square meters, in which

case maintenance would cost about $78 billion

per year. These estimates did not include design,

fabrication, testing, acquisition, installation, or

infrastructure.

Desert reflectivity is regional. The Royal Society

(2009) stated that as with other very localized

SRM technologies, this approach could change

large-scale patterns of atmospheric circulation,

like the East African monsoon that brings rain

to sub-Saharan Africa. The technology could be

reversed by removing the reflective material.

A 2009 modeling study by Ridgwell and

colleagues indicated that increasing the

reflectivity of crops by 20 percent would not

create a significant effect on global average

temperature but that reflective crops could have

an appreciable cooling effect regionally. This

study indicated that reflective crops could depress

temperatures by more than 1 degree Celsius

during summer months in a pattern broadly

corresponding to the densest cropland coverage

in the model.

Hamwey’s 2007 investigation of increasing the

reflectivity of open shrubland, grassland, and

savannah used a radiative transfer model, and

Lenton and Vaughn’s 2009 investigation of

reflective crops and open shrubland, grassland,

and savannah used an analytical approach

based on energy balance considerations, so

neither investigation can be used to evaluate

climate consequences other than global average

temperature. Hamwey did not discuss ecological

issues associated with such a massive change to

natural flora. Increasing the reflectivity of flora

could reduce overall photosynthesis, which could

reduce net carbon uptake by vegetation and crop

yields. However, this is judged to be of relatively

low risk, since photosynthesis tends to be

light-saturated during most of the growing season

(Royal Society 2009). This technology could be

reversed by replanting original flora.

Since the analyses of reflective urban areas

(Akbari et al. 2009; Lenton and Vaughan 2009)

and human habitats (Lenton and Vaughan 2009;

Hamwey 2007) were based on analytic estimates

of radiative forcing, radiative transfer, or energy

balance, their results cannot be used to evaluate

GAO-11-71 TECHNOLOGY ASSESSMENT

climate consequences other than global average

temperatures. However, reflective surfaces

could reduce air-conditioning costs (Levinson

and Akbari 2010). Effects would be reversible

by returning reflective surfaces to their

original condition.

3.3 Status of knowledge and

tools for understanding

climate engineering

Gordon (2010, 7–8) identified 26 examples

of areas of climate research that are important

to understanding climate engineering and

8 examples of climate engineering research

tools. The report described resources at several

federal agencies that could help advance climate

engineering research and gave examples of a

number of their achievements in these areas

(Gordon 2010, 8–37).

Further efforts to improve scientific

understanding related to climate engineering are

under way, but reports from DOE, the National

Aeronautics and Space Administration (NASA),

National Institute of Standards and Technology

(NIST), National Oceanic and Atmospheric

Administration (NOAA), peer-reviewed scientific

publications, and interviews with scientists

indicate that the science is characterized by

significant uncertainties. These gaps are related

to the measurement of climate variables and

models of the climate system that can simulate

the effects of climate engineering on outcomes

such as temperature or precipitation. The reports

we reviewed described key limitations related

to climate engineering science and three key

challenges to improving them: (1) resolving

uncertainties in scientific knowledge;

(2) improving the coverage, continuity, and

accuracy of observational networks used to

measure essential climate mechanisms; and

(3) developing greater high-performance

computational resources and dedicating them

to climate modeling.

3.3.1 Better models would help

in evaluating climate

engineering proposals

Best practices in technology development

recommend thoroughly testing new technologies

before employing them in essential systems

(GAO 1999). Tests usually involve controlled

experiments to understand how a technology

being developed works and to assess its

performance. However, large-scale field

testing of climate engineering technologies is

difficult (Gordon 2010, 3-4, 20, 27, and 32).

For example, according to NIST scientists we

interviewed, estimations of or assumptions

about relevant chemical, physical, and optical

properties that are acceptable for many common

applications would introduce unacceptable risk

in large-scale climate engineering experiments

that could permanently alter the chemistry of the

atmosphere.

Complex climate models such as general

circulation models (GCM) can be used to

simulate the effects of large-scale climate

engineering proposals and evaluate them without

deploying them. However, the models are only as

good as the data and the scientists’ understanding

of how the climate system works (Meehl and

Hibbard 2007; GAO 1995). Scientists attending

the Aspen Global Change Institute’s 2006

session on Earth System Models said that gaps in

climate models or inadequate data could affect

the outcomes of numerical simulations designed

to test climate engineering proposals (Meehl and

Hibbard 2007).

TECHNOLOGY ASSESSMENT GAO-11-71

General circulation models of Earth’s climate

evolved from short-term weather forecasting

models first developed almost half a century ago

(Slingo et al. 2009; McGuffie and Henderson-

Sellers 2001). Advances in computing power and

scientists’ understanding of the climate system

have helped improve the models’ simulation

capabilities (Slingo et al. 2009), but according

to a NOAA official these improvements are

still not sophisticated enough to rely on for

climate engineering. Atmosphere-ocean general

circulation models (AOGCM) are today’s

standard in climate models; they typically account

for a number of factors that can influence the

climate, such as oceans, land surface, and sea ice

(Bader et al. 2008; Meehl and Hibbard 2007).

Since 2000, AOGCM simulations have included

aerosol effects, terrestrial processes, ocean mixing,

and sea ice movement, but reports show that

these models have important limitations with

implications for simulations of the effects of

climate engineering technologies.

For example, simulations of aerosol-based

SRM technologies require not only a thorough

understanding of how aerosols behave in the

atmosphere but also a computationally intensive

representation of this behavior in a climate

model. At present, aerosol treatment is not

standardized across GCMs, and the models

generate different results in terms of predicted

temperature changes and precipitation patterns

(Kravitz et al. 2011). Climate engineering

researchers are beginning to standardize modeling

scenarios that describe actions to manipulate

the climate. This standardization would allow

researchers to compare the robustness of the

models’ responses to engineered inputs and to

investigate how simplifying assumptions and

structures used in the models can influence these

outcomes (Kravitz et al. 2011). One scientist

noted that climate chemistry models focusing

on atmospheric processes can also contribute to

scientific understanding of aerosols but can be

computationally intensive.

Earth systems models (ESM) representing the

forefront in climate models aim to account

for biological and chemical processes, such as

the carbon cycle, that are not typically present

in AOGCMs (Bader et al. 2008; Meehl and

Hibbard 2007; Washington 2006). Climate

models that included these additional processes

could help scientists discover consequences

of climate engineering proposals that are not

predicted by the current generation of models

(Meehl and Hibbard 2007). For example,

simulations of CDR-based proposals could be

influenced by improving the representation

of the carbon cycle in climate models

(Bader et al. 2008).

Scientists have identified several potential

advancements related to ESMs that could

improve their use in evaluating climate

engineering proposals:

• scientific knowledge that would facilitate

improvements in computational algorithms

that represent physical, chemical, or

biological processes;

• improvements to observational networks that

measure essential climate mechanisms;

and

• greater high-performance computing

resources dedicated to climate

engineering-related science.

Gaps or deficiencies in observational networks could also

interfere with the ability to monitor the effect of deployed

climate engineering technologies. Monitoring would allow

scientists to verify the effectiveness of technologies and help

ensure their safety.

GAO-11-71 TECHNOLOGY ASSESSMENT

3.3.2 Key advancements in scientific

knowledge could help improve

climate models

Although scientific knowledge of Earth’s physical,

chemical, and biological processes has increased

over time, it remains characterized by substantial

gaps that can affect measures of climate sensitivity

simulated by climate models (NRC 2010a; Bader

et al. 2008; Solomon et al. 2007; Meehl and

Hibbard 2007).

Increased scientific knowledge

about a number of environmental processes

could improve scientific confidence in estimates

of climate sensitivity. For example, Bader and

colleagues (2008) highlighted the importance of

improving representations of terrestrial, oceanic,

and atmospheric carbon-feedback processes

for more reliable estimates of future climate

change. About half of all anthropogenic carbon

emissions are sequestered in terrestrial or oceanic

sinks whose mechanisms and capacities are not

adequately revealed by observations (NRC 2007).

Similarly, the relative magnitude of Earth’s

energy reservoirs and the exchanges between them

are not fully understood (Trenberth and Fasullo

2010).

Scientists’ limited understanding of how

aerosols and clouds affect Earth’s energy budget

and hydrological cycle is the most important

source of uncertainty in climate models (NRC

2007). Aerosols may affect climate to the same

degree as CO

at current levels, but uncertainty

about the effect of aerosols is about five times

greater than the corresponding uncertainty about

(NRC 2007). Experts at a NASA workshop

reported that using climate models to simulate

One example of a measure of climate sensitivity would be

“the response of global mean temperature to a doubling of

[the atmospheric concentration of] carbon dioxide”

(Bader et al. 2008, 2).

A discrepancy in carbon output and uptake by Earth’s systems

remains unresolved. To preserve mass balance in today’s best

estimates of the global carbon budget requires including an

unknown terrestrial carbon sink of about 1.8 billion tons of

carbon per year (R. A. Houghton et al. 1998).

and evaluate aerosol-based SRM proposals to

modify the climate is limited by the lack of

models that explore how these aerosols would

affect stratospheric ozone and the biosphere

(Lane et al. 2007).

3.3.3 Better observational networks

could help resolve uncertainties

in climate engineering science

Observational sensing systems such as satellites

and ground-based stations collect data that help

scientists track climate trends and model climate

mechanisms. Scientists have expressed several

concerns about the coverage, continuity, and

accuracy of observational networks that gather

data related to climate mechanisms that are

central to climate engineering technologies.

Observational network abilities depend in part

on where sensors are placed and the density of

their distribution (OSTP 2010; Ohring 2007).

Climate engineering scientists have expressed

concern about the adequacy of observational

networks in the atmosphere (Gordon 2010,

23). For example, some scientists have criticized

the sparse distribution and output of sensors

in the upper atmosphere, where a number

of processes have implications for CDR and

SRM technologies (NRC 2010a). In particular,

scientists from NOAA and Oak Ridge National

Laboratory said that CO

measurements from

these sensors may be insufficient to permit

conclusive statements about the effects of a given

CDR technology. Upper atmosphere observations

of the types of aerosols under consideration in

some SRM proposals are also rare. Moreover,

instruments that measure the optical properties

of aerosols were recently eliminated from two

satellites in the Joint Polar Satellite System

(Gordon 2010, 15).

TECHNOLOGY ASSESSMENT GAO-11-71

Scientists have also expressed concern about the

continuity of measurements by observational

networks. Scientists have noted that deferring

the implementation of adequate observational

networks could miss opportunities to collect

data on infrequent and unpredictable natural

events, such as large volcanic eruptions, that

could help scientists understand mechanisms

related to climate engineering (Asilomar Scientific

Organizing Committee 2010; Gordon 2010,

23).

Scientists have also criticized the lack of

redundancy in observational networks, which

could create a gap in the measurement record if a

single satellite or sensor were to fail (OSTP 2010;

Ohring 2007; NRC 2007). For example, NASA’s

Glory Climate Satellite, intended to collect data

on aerosols and solar energy in the atmosphere,

recently failed to reach orbit at its launch.

The continuity of measurements can also be

affected if programs to collect data are not

sustained over a long period of time. For

example, federal budget cuts in the past decade

have cancelled, delayed, or degraded the

collection of data from NASA’s Earth Observing

System satellites, whose instruments and sensors

measure essential climate variables such as Earth’s

radiation budget, the global distribution of CO

concentrations of methane and other greenhouse

gases, air temperature and moisture content,

cloud cover, and sea surface temperatures (NRC

2010a). Further, a 2007 NRC report predicted

that the nation’s system of environmental

satellites could decline dramatically and the

number of operating sensors and instruments on

NASA’s spacecraft would decrease by about

The eruption of Mount Pinatubo in 1991 released a large

quantity of sulfate aerosols into the atmosphere, causing

average global temperatures to fall. Scientists attending the

2010 Asilomar conference said that current observational

networks are inadequate to collect data following such an

eruption that could help improve scientific knowledge about

atmospheric mechanisms related to aerosol-based SRM

technologies.

40 percent by 2010 (NRC 2007). Scientists

have also noted the difficulty of comparing

continuous observations measured by different

satellites or sensors without any overlap in their

observation periods.

Scientists have expressed concern about the

accuracy of data collected from existing sensing

devices (NRC 2007). For example, according to

NIST scientists, unknown drifts in instrument

data can cause measurements to show misleading

evidence of change or false trends. Additionally,

because most operational or weather satellite-

based sensors share a common heritage, an

artificial trend in a reading from one sensor is

likely to exist in similar readings from other

versions of the sensor, which would bias the

measurements if the drift remained undetected.

Moreover, large variations exist in solar radiation

measurements even over small geographic areas

and the causes are uncertain.

Satellite programs developed to monitor and

track local weather patterns might not be accurate

or precise enough to measure long-term global

climate change (Fraser et al. 2008). Climate-

relevant signals are extremely small compared to

fluctuations in weather and temperature observed

daily, seasonally, or annually (Ohring 2007). For

example, a decade’s anticipated average global

temperature change is about 0.2 degrees Celsius,

or about 1/50th of the temperature change that

accompanies typical weather events. It is similarly

difficult to accurately measure small variations in

incoming or outgoing solar radiation on the

order of 0.01 percent over decades without

According to NIST scientists, both ground- and space-

based measurements exhibit these types of variation. The

space-based variations are largely attributable to calibration

inaccuracies that can largely be corrected by adjustments using

measurements taken during satellite overlap. The ground-

based variations are both geographic and temporal and are

likely to include contributions from global dimming, urban

aerosols, and sensor calibration inaccuracies.

GAO-11-71 TECHNOLOGY ASSESSMENT

adequate optical instruments. Measuring

radiation with accurate sensors is critical to

advancing climate science: IPCC has reported

that most climate change uncertainty derives

from changes in Earth’s outgoing broadband

radiation (J. T. Houghton et al. 2001).

Within the federal government, steps are being

taken to resolve some of these concerns, which

might improve the ability to assess climate

engineering technologies or proposals. Various

agencies have proposed a long-term measurement

strategy in Achieving Satellite Instrument

Calibration for Climate Change (Ohring 2007).

Satellite missions are being designed to help

calibrate and reconcile some of the data received

from existing climate measuring devices. For

example, NASA’s Climate Absolute Radiance and

Refractivity Observatory (CLARREO) mission

is intended to yield a benchmark data record for

detecting, projecting, and attributing change in

the climate system.

CLARREO would constitute a major effort to

correct systematic biases and discontinuities

in satellite-based climate measurements and to

provide a robust climate reference point for future

sensors that is traceable to accepted physics-based

standards, called the International System of

Units. Traceability ensures that environmental

measurements are comparable, independent of

the organization or country making them. The

National Science Foundation (NSF) is sponsoring

the construction of an integrated, Earth-based

observation system called the National Ecological

Observatory Network that will collect data

across the United States on climate and land

use changes and the effect of invasive species on

The President’s fiscal year 2012 budget request for NASA

cut much of the funding for the CLARREO mission and

called for an extended preformulation period for the mission

and science team to identify implementation options for

obtaining climate change measurements without using

CLARREO satellites.

natural resources and biodiversity.

According to

NSF, it will be the first observatory network that

can both detect and forecast ecological change on

a continental scale over multiple decades. Gordon

notes that the network could inform research

on several climate engineering technologies,

including land-use management and biochar

(Gordon 2010, 10).

3.3.4 High-performance computing

resources could help advance

climate engineering science

Advances in computing could help scientists

improve models used to simulate essential climate

mechanisms and outcomes related to climate

engineering. Limits in computational resources

demand that existing climate models simplify

certain processes essential to climate engineering

instead of computing them numerically (Bader et

al. 2008). Unlike short-term weather modelers,

climate modelers have not moved to higher

resolutions.

Instead, they have used modern

computational power to include additional

physical components in the calculations.

This

is particularly important for climate engineering

where, for example, stratospheric chemistry (to

treat stratospheric aerosol processes) and the

hydrological cycle (to treat cloud brightening)

are important. A typical climate model represents

Earth’s system as a grid of boxes anywhere from

100 to 300 kilometers on a side, which is larger

The network is expected to be fully operational in 2016.

Grids for atmospheric circulation models have been refined

from resolving areas the size of Colorado in 1990 to the size of

South Carolina in 1995, and to about the size of Rhode Island

(4,000 km

) in 2007. Meanwhile, weather models have been

run with a resolution of less than 1,000 km

for over 20 years.

More computer resources can be used for finer numerical

grids, greater number of runs for statistical estimation, or

more climate processes; consensus on the optimal resource

allocation does not exist.

TECHNOLOGY ASSESSMENT GAO-11-71

than a typical cumulus cloud of about 1 square

kilometer (Slingo et al. 2009; Bader et al. 2008).

Other significant climate features like oceanic

eddies also act on a much smaller scale than the

resolution current climate models support. Finer

resolution that could be supported by increased

computing power would help improve climate

models’ representations of atmospheric and

oceanic circulation (Bader et al. 2008).

Computing advances could also facilitate the

use of climate models to predict outcomes

for geographic regions or across shorter time

intervals. Scientists at NOAA’s Earth Systems

Research Laboratory said that finer resolution

could improve climate models’ predictions

of regional changes that could be useful in

evaluating climate engineering proposals. A

climate scientist and a systems engineer also

noted the potential value for climate engineering

of greater precision in predicting regional changes

in temperature and hydrological processes than

existing models provide. They also observed that

studies of climate engineering could benefit from

simulations over shorter time intervals than are

used in existing models.

Officials at NOAA have

predicted that at the historical rate of increase in

computing power, supercomputers able to run

cloud-resolving ESMs with a grid size of a few

kilometers should be available by 2025.

Some federal agencies are already developing

tools that would take advantage of anticipated,

massively parallel, fine-grain computational

architectures based on thousands of graphics

Existing models were designed to distinguish long-term

climate trends (Fraser et al. 2008).

processing units (GPU).

For example, NOAA is

encoding an ESM to operate with small amounts

of local memory that will allow it to run on

these GPUs. Additionally, DOE, NOAA, and

the National Center for Atmospheric Research

purchased supercomputers such as the Cray XT6

and Cray Baker computers with funding from

the American Recovery and Reinvestment Act

of 2009, and scientists at these agencies hope to

develop an ESM by 2025.

As table 3.1 and table 3.2 show, climate

engineering technologies are in early stages of

development and have variable and uncertain

cost factors, while uncertainty surrounds

their potential effectiveness and potential

consequences. Moreover, gaps in scientific

knowledge, data, and computing resources

challenge the models of climate mechanisms

related to climate engineering.

The advent of GPUs follows on three revolutions in

computing operations: (1) integrated circuits, (2) vector

computing, and (3) parallel computing (which made

current forecasting possible). GPUs complete intense,

split-second calculations efficiently to render virtual

representations of the real world.

GAO-11-71 TECHNOLOGY ASSESSMENT

TECHNOLOGY ASSESSMENT GAO-11-71

Because climate engineering technologies

are currently immature, we explored future

prospects for climate engineering research by

obtaining a wide range of expert views. We

obtained expert views on the future of research

in three stages: (1) 6 experts met with our

Chief Scientist to construct alternative future

scenarios for climate engineering research, (2)

28 additional experts representing a wide range

of professional disciplines and organizational

affiliations shared their views about the future

in response to the scenarios, and (3) some of the

experts participating in the Meeting on Climate

Engineering, which we convened with the help

of NAS, volunteered their thoughts about the

future.

(In the appendices to this report, sections

8.3 and 8.4 present the scenarios and list the

experts who served as scenario-builders, section

8.5 lists the experts who provided comments in

response to the scenarios, and section 8.6 lists

the experts who participated in the meeting

we convened with the assistance of NAS.)

Altogether, 45 experts contributed views on the

prospects for climate engineering research across

the next 20 years.

Among the experts we consulted, primary areas of expertise

spanned two broad categories: (1) physical science or technical

research related to climate engineering or climate change

and (2) social science, law, ethics, or other related fields with

applications in climate engineering or climate change.

Although we attempted to consult diverse experts representing

the full range of views on climate engineering, the relative

numbers who expressed a particular view to us may not reflect

the entire community of those with similar kinds of expertise.

However, for transparency, we provide the specific numbers

of experts who told us that they advocated certain views. We

note that not all experts expressed an opinion on all issues.

Briefly, we found the following:

• The majority of the experts we consulted

advocated starting significant climate

engineering research now or in the very near

future.

Among the reasons they gave for

starting research now is the anticipation that

two decades or more of research will be needed

to make substantial progress toward developing

and evaluating climate engineering technologies

with the potential to reduce emerging or future

risks from climate change. Research advocates

also envisioned safeguards to protect against

potential adverse consequences or risks arising

from the research.

• A small number of those we consulted

opposed starting such research, in part to

prevent negative consequences either from

the research or from deploying technologies

developed from it.

• The majority envisioned a federal effort that

would direct and support research on climate

engineering with specific features such as (1) an

international focus, (2) engagement of both the

public and decision-makers, and (3) foresight

considerations to help anticipate emerging

research developments and their opportunities

and risks.

Two-thirds of the experts we consulted about the future

(31 of 45) advocated starting significant research now or in

the very near future.

Four of the 45 experts we consulted about the future stated

that they opposed research on climate engineering. (One of

these 4 made exceptions for certain kinds of research, such as

computer modeling.)

Twenty-nine of 45 experts envisioned a federal research effort,

and as detailed below, 26 of these mentioned one or more of

these three features.

4 Experts’ views of the future of climate

engineering research

GAO-11-71 TECHNOLOGY ASSESSMENT

• Experts identified many trends as potentially

affecting research, including the pace of climate

change, emissions-reduction developments, and

scientific breakthroughs.

4.1 A majority of experts

called for research now

The majority of the experts we consulted

about the future advocated starting significant

research now or in the very near future, largely

from concern about future climate change and

the need to reduce its risks.

In this report, we

define “starting significant climate engineering

research” as increasing research beyond that

now being conducted. We had reported earlier

that a relatively small amount of federal research

is directly focused on climate engineering

(GAO 2010a, 19).

The advocates of research

now—and some experts who did not indicate

whether they advocated starting research

now—anticipated that research will produce

technologies or evaluative information or both

that might help reduce risks associated with

climate change or uninformed responses to it.

Risks from climate change might include, for

example, potential breakdowns in food and

water supply chains (as climate change brings

precipitation changes and rises in sea level),

mass migration, and international conflict.

More than half of these proponents anticipated

Thirty-one of 45 experts said they advocated research now or

in the near future, and 4 opposed research. The remainder did

not clearly state whether they advocated starting research now.

Specifically, we reported that 13 federal agencies had

identified at least 52 research activities, totaling about

$100.9 million, as relevant to climate engineering in

fiscal years 2009 and 2010 (GAO 2010a)—$1.9 million

for activities to investigate specific climate engineering

approaches and $99 million related to conventional mitigation

strategies or basic science that could be applied to improving

understanding of climate engineering.

that substantial research progress will take

time—perhaps two decades or more—or stated

that we cannot and should not wait for a crisis.

Additionally, research advocates indicated that a

cautious risk management approach could help

reduce research-related risks.

Those who advocated research now either did so

urgently because they anticipated a definite need

for climate engineering or viewed research as

an insurance policy. For example, some warned

against (1) losing the ability to prevent what they

perceived as potentially irreversible changes or

(2) being unprepared for a crisis. With respect

to the latter, the report’s scenarios (1) describe

how leaders who are unprepared while under

heightened pressure to act quickly in a crisis

might decide to deploy inadequately understood,

risky technologies and (2) present the view that

informed leaders might decide not to deploy risky

technologies.

Others who called for research now recognized

the uncertainty of the future and viewed climate

engineering research

“as an insurance policy against the

worst case scenarios”

in the longer-term future. One said that the

nation should

“make investments [in] . . . fundamental

research . . . to be able to react quickly [if

needed]. . . . [Spending to limit risk] on

climate, terrorism, national defense,

We note, however, that national leaders might not base

decisions on information about research results, even if such

information were available.

TECHNOLOGY ASSESSMENT GAO-11-71

nonproliferation, should be viewed

identically.”

Overall, those calling for research now reflected

foresight literature that warns against falling

behind a potentially damaging trend, as

illustrated in figure 4.1. Those advocating

research now recognized important cautions,

discussing two types of risk associated with

research: (1) risks from conducting certain kinds

of research (for example, large-scale field trials

of potentially risky technologies) and (2) risks

from using or misusing research results (for

example, deploying risky technologies developed

This insurance view reflects the hedging strategy described

in foresight literature whereby, faced with uncertainty,

decision-makers choose a strategy that they anticipate will

work reasonably well across all alternatives to avoid potentially

disastrous low-probability outcomes (Popper et al. 2005).

from theresearch).

Various research advocates

therefore suggested potentially complementary

remedies such as

• managing risks (from research and using its

results) with strategies like those outlined in

box 4.1, which have been highlighted in

the literature;

• evaluating the risk of deploying specific

technologies, in advance, which could lead to

taking some risky technologies off the table;

and

Overall, of the 31 experts advocating research now,

27 recognized risks associated with it, including risks

from conducting it (11 experts) and from using its

results (26 experts). One advocate who believes that it

is urgent to start research now also said that guidelines

are needed to decide when research “has become too

dangerous to continue.”

POTENTIALLY DAMAGING TREND

TIME PERIOD

Current Near-term future

(somewhat uncertain)

Longer-term future

(very uncertain)

Current, potentially damaging trend

Projected, with early intervention

Projected, without intervention

Projected, with late intervention

Minimal

Reversible

Irreversible and

very costly

Figure 4.1 Taking early action to avoid potentially damaging trends: Illustration

from foresight literature. Source: GAO adapted from Rejeski (2003).

GAO-11-71 TECHNOLOGY ASSESSMENT

• setting international research limitations or

guidelines.

We reported earlier (GAO 2010b, 13) that in 2008 the

parties to the London Convention and London Protocol

issued a decision stating that ocean fertilization that is

not legitimate scientific research is contrary to the aims of

the agreements and should not be allowed. The treaties’

scientific bodies are developing an assessment framework for

countries to use and evaluate whether research proposals are

legitimate scientific research (GAO 2010a, 33). In 2010, the

parties to the Convention on Biological Diversity invited

countries to consider the following guidance: (1) ensure

that ocean fertilization activities are consistent with the

London Convention and Protocol and decisions issued by

the conference of the parties to those treaties and (2) ensure

that except for certain small-scale scientific research studies,

no climate-related geoengineering activity that may affect

biodiversity take place until there is an adequate scientific

basis on which to justify it and appropriate consideration of

the associated risks and impacts.

As we discussed above, research advocates

suggested the study of climate engineering risks,

and we earlier reported (GAO 2010a) that

experts had told us that potentially “unintended

consequences . . . require further study.”

Some research advocates qualified their

positive view of climate engineering research

with the proviso that emissions reduction

efforts be continued. They warned that if the

concentration of CO

continues to rise into

the long-term future, deploying SRM—and

increasing it over time to maintain acceptable

Additionally, of the 52 research activities federal agencies

identified as relevant to geoengineering in our 2010 report,

only one project’s activity description specifically mentioned

risk (GAO 2010a).

Box 4.1: Climate engineering research: Risk mitigation strategies from the literature

• The research community’s voluntary self-governance and development of

norms and best practice guidelines for open and safe research

• Required examinations of ethical, legal, and social implications in federally

funded research projects

• Interventions that bring social scientists, ethicists, or trained risk assessors directly

into laboratories to ensure early accounting for risks and social and ethical issues

• Application of an institutional review board concept to climate engineering research

• Commissioned and independently conducted interdisciplinary risk assessments

• A multistage approach in which initial research (for example, computer modeling and

laboratory studies) investigates risks before progressing to small-scale field studies,

which in turn provide added information on risks before progressing to large-scale

field experiments

• Study of risk trade-offs and analysis of options for reducing overall risks

• Developing norms for deployment decisions, facilitated by research activity

Source: Olson forthcoming; Morgan and Ricke 2010; Victor 2008; Graham and Wiener 1995.

Institutional review boards typically review research projects that use humans so as to protect their rights and welfare.

However, the concept could be expanded to require an institutional review of research for field experiments

that use Earth as a subject. IRB review requirements could be linked directly to federal research grants given for

climate engineering.

TECHNOLOGY ASSESSMENT GAO-11-71

temperatures—would lead to serious risk. That

is, should extensive SRM deployments fail or be

discontinued for any reason,

“the bounce-back effect [of sudden

warming] would be staggering.”

Some research advocates also indicated that

reducing emissions (and using apparently safer

CDR technologies, such as direct air capture and

sequestration, if needed to reduce build-up)

would logically reduce the need for potentially

risky SRM deployment.

Finally, a research advocate who reviewed this

report emphasized the need to consider the net

effect of (1) the risks of climate change without

climate engineering, (2) the potential reduction

of climate risks through climate engineering, and

(3) the introduction of possible new risks through

climate engineering.

4.2 Some experts opposed

starting research

We noted above that a small number of the

experts we consulted opposed starting significant

research on climate engineering.

Some thought

that pursuing further research would, in the

words of one commenter, open a Pandora’s box

better left unopened. Opponents of research

viewed climate engineering as technological

hubris or as likely to be ineffective or not

needed. Those who said that climate engineering

is not needed either believed that climate

change has been exaggerated or preferred other

approaches, such as “building ecosystem and

Four of the experts we consulted opposed conducting

research. Additionally, because of questions some reviewers

of a draft of this report raised, we note that three of the four

opponents of research had primary expertise in fields such as

social science, law, ethics or other related fields (rather than

physical science); these three provided the direct statements of

research opponents that we quote in this section.

community resilience to respond to climate

change,” “adopting more sustainable agricultural

policies,” or “making [a] massive investment in

energy efficiency.” However, the most strongly

expressed opposition to climate engineering

research concerned risks. One research opponent

envisioned situations in which stratospheric

aerosols would produce conflicts or catastrophic

results in some parts of the world:

“There are wars waged over the position

and density of the clouds, rainfall

patterns, ocean alkalinity, and volcanic

eruptions as confusion prevails over what

phenomena are natural and which are

manmade. Different, often conflicting

experiments are sponsored by different

countries . . . .

“. . . the precipitation patterns over

large parts of Africa and Asia, which are

already suffering from drought and food

insecurity . . . [are disturbed by the SRM

deployment and eventually] hundreds

of millions of people die because of crop

failures and chaotic weather events . . . .

[A] very small number of people control

the climate levers, [and . . . ] global

tensions rise.”

The research opponents in our study did not

envision varied strategies for managing, reducing,

or avoiding risks from research or technologies

These risks (international conflict, drought, and famine)

that an expert cited as potentially deriving from climate

engineering research and deployment are similar to those

associated with climate change. Research opponents also

pointed to other possible risks; for example, some

potential SRM technologies have been associated with

the depletion of ozone and interference with the use of

solar-energy technology.

GAO-11-71 TECHNOLOGY ASSESSMENT

developed from it. One opponent of research

endorsed international moratoriums and said that

“It is illogical to assert that the best

risk-avoidance strategy is to increase

research. The best way to avoid responses

that are extremely high risk is not to

research them more; it is to make sure,

through legally binding agreements,

that they are prohibited.”

While research advocates suggested evaluating

technologies in advance of deployment, some

opponents thought that, as one said,

“the effects of human intervention are

impossible to predict with a high degree

of certainty. Any large-scale attempt to

tame the climate system . . . has a high

probability of backfiring.”

Finally, some research opponents were concerned

about moral hazard—that is, the possibility that

the results of climate engineering research would

“undermine the political will to

reduce emissions.”

Some research opponents feared that climate

engineering would be substituted for, rather than

used to complement, emissions reduction efforts.

One research opponent suggested that

“Political leaders . . . faced with the choice

of politically difficult unilateral reductions

in carbon emissions and the illusion of a

techno-fix, [will] go for the latter.”

As we discussed in the previous section, some

advocates warned of negative outcomes if climate

engineering, particularly SRM, were pursued in

the absence of emissions reduction.

4.3 A majority of experts

envisioned federal research

with specific features

We reported earlier that the United States does

not have a “coordinated federal strategy for

geoengineering, including guidance on how to

define . . . geoengineering activities or efforts

to identify and track . . . funding related to

geoengineering” (GAO 2010a, 23). In that

report, we recommended that

“the appropriate entities within the

Executive Office of the President

(EOP), such as the Office of Science

and Technology Policy (OSTP), in

consultation with relevant federal

agencies, develop a clear, defined, and

coordinated approach to geoengineering

research in the context of a federal

strategy to address climate change that

(1) defines geoengineering for federal

agencies; (2) leverages existing resources

by having federal agencies collect

information and coordinate federal

research related to geoengineering

in a transparent manner; and if the

administration decides to establish a

formal geoengineering research program,

(3) sets clear research priorities to inform

decision-making and future governance

efforts.” (GAO 2010a, 39)

OSTP neither agreed nor disagreed with our

recommendation but provided technical and

other comments. With respect to the context

of a federal strategy to address climate change,

TECHNOLOGY ASSESSMENT GAO-11-71

we note that other approaches to addressing

climate change include efforts to (1) reduce

emissions and (2) adapt to climate change.

In our work for this report, we found that experts

who advocated starting significant research now

generally also advocate or envision a federal

research effort with specific features.

That is,

they envision federal research that would foster

the development of technologies like CDR

and SRM, rigorously evaluate related risks, and

include specific features such as

• an international focus,

• engagement of the public and national

decision-makers, and

• incorporation of foresight considerations aimed

at identifying new opportunities, anticipating

new risks, and adapting research to emerging

trends and developments.

As outlined in this report’s overview of the

technologies, knowledge is currently limited

on proposed CDR and SRM technologies, and

experts’ comments to us further suggested that

planning might need to precede the first phase of

any federal research effort.

Some research advocates who envision a U.S.

climate engineering research effort explained

that other nations, the United Kingdom among

them, are already studying these technologies

or establishing programs.

They said that the

absence of a U.S. research effort could leave

Of the 31 experts who advocated starting research now,

29 also advocated or envisioned a federal research effort;

26 of these envisioned one or more of the three specific

features discussed in this section. Some experts also anticipated

the development of technologies by the private sector.

One expert told us that some nations’ research may be hidden

because it is not specifically labeled as climate engineering or

because it is covert.

the United States “without a seat at the table,”

unprepared to play a leading role, or unable to

respond to other nations’ actions. One advocate

of a U.S. research effort said that

“If it ever becomes necessary to deploy

geoengineering techniques, doing so will

be a momentous decision for humanity.

The United States should be prepared to

play a leading role in the decision, and it

should be unthinkable that the decision

could be made without substantial input

from the U.S. scientific and technical

community.”

Others imagined a future in which individual

nations would unilaterally engage in SRM; one

motivation might be to resolve local or regional

problems caused by climate change (Morgan

and Ricke 2010). On one hand, such actions

could have transboundary or global SRM effects,

conceivably raising issues of national security,

stimulating other nations to respond, or requiring

a U.S. response. On the other hand, the risk

of unilateral action might be reduced with

cooperative international research that fostered

trust and cooperation among nations on issues

pertaining to climate engineering.

For reasons such as these, many of the research

advocates in our study suggested an international

approach to federally sponsored research.

Suggested activities included

One approach to international research cooperation is

illustrated by the International Space Station, with its five

main partners:Canada, Japan, Russia, the United States, and

the European Space Agency (which includes a number of

countries) (GAO 2009c).

Twenty-four experts (of 31 who advocated climate

engineering research now) specifically envisioned an

international approach for federal research.

GAO-11-71 TECHNOLOGY ASSESSMENT

• studying strategies for responding to situations

arising from insufficient international

cooperation in the use of climate engineering;

• sponsoring or encouraging joint research

with other nations (including developing or

emerging industrial nations) because this might

(1) help the United States keep pace with

other nations’ research; (2) facilitate rigorous,

transparent evaluation of new technologies that

others develop; and (3) foster cooperation and

consensus—or an evolving set of norms about

conducting research, which might, in turn,

foster support for guidelines;

and

• studying how the responsibilities of nations

that deploy these technologies could impinge

on others’ geopolitical equity, human rights,

and justice—which would logically be most

important for vulnerable or poor populations.

Other international issues suggested for research

included (1) studying how to define climate

emergencies and achieve international agreement

on responses to them and (2) exploring issues

concerning military engagement in climate

engineering research.

The possibility of U.S. leadership in

internationally focused research was suggested,

as was cooperation:

One of our scenarios describes the lessened possibility of

conflict because nations, having cooperated on research, have

a basis for cooperating in a sudden crisis. Our 2010 report

indicated that “several of the experts we interviewed as well

as the NRC study emphasized the potential for international

tension, distrust, or even conflict over geoengineering

deployment” and discussed international agreements and

governance challenges (GAO 2010a, 17 and 26–37).

“What the U.S. can do . . . is to lead

the process of framing the [climate

engineering] issue as one requiring

global collaboration and evidence-based

decision-making processes that focus

not only on macro results but also on

fairness in distributional aspects of action

versus inaction.”

One expert said that in a substantial,

internationally focused U.S. research effort,

the United States could lead by example,

emphasizing values such as transparency and

attention to risk issues.

The engagement of researchers with the public

and with U.S. decision-makers (and possibly

international leaders) was another desirable focus

for a federal research effort, according to research

advocates.

Their views included statements that

• engagement can foster shared learning

across national leadership, the general

public, and the research community;

help ensure transparency; build shared

norms; and bring an informed

“democratic process [to] . . . decisions

that . . . broadly affect society;”

• engagement results might help frame

research agendas to reflect the concerns

and needs of the public and decision-

makers; and

• information provided to the public

and decision-makers might address

Twenty-three experts (of 31 who advocated starting research

now) favored engaging the public or national leaders or both

in a federal effort.

TECHNOLOGY ASSESSMENT GAO-11-71

• (1) the systemic risks of the various

climate engineering approaches,

(2) trade-offs in pursuing alternative

strategies, and (3) analyses of ethical,

economic, legal, and social issues.

A broad, multidisciplinary research agenda

consistent with these views is discussed in the

foresight scenarios we developed for this report.

Our discussion of risks (earlier in this section)

indicated that uninformed national or global

leaders who were under heightened pressure

in a perceived climate crisis might make hasty

choices, whereas informed leaders might make

a more measured response. Logically, the same

might be true of the general public. That is,

public engagement in advance of a crisis could

help ensure that public concern about harm from

technologies is addressed in advance (through

research on benefits and risks), that research

results are appropriately conveyed to the public,

and that public expectations are consistent

with likely real-world consequences. In sum,

communication among researchers, the public,

and decision-makers might help prepare the

nation for a measured response to a future crisis.

Some advocating a federal research effort also

envisioned its incorporation of foresight activities

designed to (1) anticipate emerging directions

in developing climate engineering technologies

and new or changing risks associated with such

directions and (2) help research keep pace with

other developing trends that could affect the

research agenda and support.

Some examples

of foresight activities are communicating with

other researchers in related areas, monitoring or

surveying research, and using horizon scans and

Eighteen experts (of 31 who advocated starting research now)

specifically envisioned an anticipatory, foresight approach for

federal research.

other futures methods that could help anticipate

and track relevant developments and potential

new risks.

One research advocate also suggested

exploring low-probability, high-impact events

(described by Taleb 2007) with game theory or

scenario planning.

Other examples include iteratively monitoring a

variety of developments and trends and, where

appropriate, supporting studies that obtain

better evidence on them. This could help guide

decisions about forward directions (GAO 2008b,

67–68) and is compatible with other suggestions

for adaptively managing climate engineering

research. (With respect to the latter, experts in

our study endorsed adaptive management to

better achieve continuous improvement, based

on (1) changing practices over time in response

to experience and performance assessment and

(2) learning how to intervene in a complex,

imperfectly understood climate system.

)

Finally, the overall results of our communications

with experts indicated uncertainty, or at least a

diversity of views, on what technical research and

evaluation will be needed for specific CDR and

SRM technologies. Some experts noted the lack

of any map or forward-looking plan showing

how climate engineering research might progress

along various paths. We also found that experts

expressed widely different views on

A horizon scan is a systematic examination of ongoing trends,

emerging developments, persistent problems that may have

changed, and novel and unexpected issues. Horizon scans are

sometimes structured strategically to consider potential threats

and opportunities separately.

For example, Long (2010) has said that an adaptive approach

is appropriate for climate engineering because climate is

a complex, nonlinear system. Such an approach might

include monitoring the results of an intervention, comparing

observations to predictions, deciding whether the research is

proceeding in the right direction, and making a new set of

decisions about what to do.

GAO-11-71 TECHNOLOGY ASSESSMENT

• the scope of whatever global climate

engineering efforts might eventually be

implemented or deployed and

• the level of effort or funding needed

for research.

For example, experts variously characterized

the scope and scale of the deployment of

stratospheric aerosols in terms of (1) operations

that “rogue” actors might carry out unilaterally

or, in contrast, (2) huge operations that might

amount to “the largest engineering project in the

history of people.”

Some experts we consulted suggested that

research funding might start with as little as a

few million dollars. The scenarios developed for

this report suggest that more effective research

would have a considerably higher budget but they

do not specify an amount. We reported earlier

that 13 federal agencies had identified at least 52

research activities relevant to climate engineering

in fiscal years 2009 and 2010 (GAO 2010a)—

with funding of $1.9 million to investigate

specific climate engineering approaches. Much

larger amounts have funded activities related to

conventional mitigation strategies or basic science

that could be applied to improving scientific

understanding of climate engineering.

Because information about climate engineering

and related research is limited, one of the experts

who advocated federal research suggested that a

federal effort begin with initial developmental

work to delineate scale and cost. (Further research

might then be planned and potential research

Additionally, 10 experts told us that either analytical

information on the cost of a potential climate-engineering

research program is lacking or they did not know of such

information.

An additional $99 million supported these other activities.

costs estimated (GAO 2009b).) According to

another expert, planning efforts would benefit

from the development of an overall research

strategy, including, for example, a

“multidisciplinary framework for

integrated systems analysis . . . and risk

assessment tailored to designing and

evaluating geoengineering technologies

and their potential deployment as subscale

experiments.”

4.4 Some experts thought that

uncertain trends might

affect future research

When the experts we consulted envisioned

research with a foresight component, they saw the

following as relevant and potentially critical to

track. First, signals of impending climate-related

events would be relevant because these could

potentially heighten the urgency and priority

of the research. An example might be a collapse

of ocean fisheries attributed to global warming

and ocean acidification, with depletion of food

supplies in vulnerable areas. Second, trends

in policies for or new approaches to emissions

reduction could affect prospects for CDR’s

implementation. Our scenarios illustrate the

view that establishing carbon constraints would

encourage an anticipation of the use of CDR

research, creating an incentive for research and

innovation.

Experts differed in assessing how

CDR research might develop in the absence

of significant carbon constraints. Some said it

Carbon constraint policies aim to limit or reduce carbon

emissions. Greenhouse gas emissions pricing is one type of

carbon constraint that would encourage people to reduce

emissions by making them more expensive. Despite ongoing

debate over climate change legislation, the U.S. Congress did

not enact legislation in 2010, and its prospects are uncertain.

TECHNOLOGY ASSESSMENT GAO-11-71

would be difficult to sustain research or deploy

CDR technology without carbon constraints,

while others disagreed, citing the possibility

of deployment through a major public works

program (Parson 2006).

Also relevant would be

developments in sequestration related to advances

in carbon capture and storage.

Other potentially important areas to track

are nanotechnology and synthetic biology

breakthroughs (Rejeski 2010; Shetty et al.

2008); advances in these areas might bring

new developments in climate engineering

technologies. Examples include future

“programmable plants” that would sequester

more carbon than natural plants and airborne

microbes that would consume greenhouse

gases. However, such developments might

entail new risks.

Future research breakthroughs might lead to or

create new low-cost, low-carbon technologies

and thus speed emissions reduction. One expert

envisioned no-carbon energy sources like solar

power costing less than carbon-based energy.

Developments such as these could have important

implications for the future role of CDR.

Additionally, experts thought trends in public

opinion on climate engineering research might

affect support for research or specific projects.

Monitoring trends in public opinion could

be a key element of public engagement; for

example, it might signal a need to study the safety

implications of certain kinds of studies.

Finally, experts (1) suggested links between future

developments in climate engineering and possible

international tensions or conflicts that might

develop from economic issues, cultural changes,

or demographic shifts and (2) indicated that

low-probability, high-impact events might affect

future research. They suggested examples of the

latter, such as an SRM experiment’s coinciding

with a natural volcanic eruption and producing

unprecedented cooling; abrupt changes in

ocean currents sharpening climate differentials;

catastrophic alterations in weather patterns;

geopolitical instability caused by widespread

and prolonged famine in Africa or the Indian

subcontinent attributable to global warming; a

biotechnology disaster’s leading to strong public

sentiment against technological interventions;

the low-cost distribution of locally affordable

technology’s reducing shipping-related carbon

emissions; or sudden cooling from an asteroid hit.

If research planners believe that some low-

probability events represent sufficient risks

or opportunities, they might decide either on

contingency planning or on hedging—that is,

selecting a strategy that works reasonably well

across a variety of outcomes, including certain

low-probability, high-impact events (Popper

et al. 2005).

GAO-11-71 TECHNOLOGY ASSESSMENT

TECHNOLOGY ASSESSMENT GAO-11-71

Because climate engineering technologies are

potentially risky and could affect a large number

of people and because experts have noted the

importance of public engagement on this issue,

we collected baseline measures of public opinion

on climate engineering research among U.S.

adults today. We analyzed survey responses

from 1,006 U.S. adults 18 years old and older

(representing the U.S. public) to address our

third objective concerning the extent of awareness

of geoengineering among the U.S. public and

how the public views potential research into and

implementation of geoengineering technologies.

We found that the majority of the U.S. public is

not familiar with geoengineering. Because public

understanding of geoengineering is not well

developed and public opinion in this area may be

influenced by a variety of factors that may change

over time, it is important to note that the results

we report are not intended to predict future U.S.

public views. Rather, our results provide valuable

baseline information about current awareness of

geoengineering and how the U.S. public might

respond if it learned more about geoengineering.

Knowledge Networks Inc. fielded the survey of a statistically

representative sample of 1,006 respondents July 19 to

August 5, 2010, using its online research panel. We used

the term “geoengineering” in our survey questions and other

information we provided about climate engineering because

we had used the term in earlier work. All estimates from the

survey are subject to sampling error. In terms of the margin

of error at the 95 percent confidence level, the sampling error

for estimates based on the total sample is plus or minus 4

percentage points and, for estimates based on subgroups of the

sample, is plus or minus 9 percentage points, unless otherwise

noted. Because the overall response rate was low and sources

of nonsampling error may have contributed to total survey

error, we rounded survey results to the nearest 5 percentage

points. We describe our methodology in more detail in

section 8.1.3.

Because the public lacked familiarity with

geoengineering, we provided survey respondents

with basic information about geoengineering

technologies before asking questions about them.

Our key findings are that if the public were given

the same type of information that we gave our

survey respondents, then

• about 50–70 percent of the U.S. public across

a range of demographic groups would be

open to research on geoengineering.

Many

survey respondents expressed concern about

the potential for harm from geoengineering

technologies, but a majority also said they

believe research should be done to determine

whether these technologies are practical;

• about half of the U.S. public would support

developing geoengineering technologies. At the

same time, about 75 percent would support

reducing CO

emissions and increasing reliance

on solar and wind power;

• about 65–75 percent of the U.S. public

would support a great deal, a lot, or a moderate

amount of involvement by the scientific

community, a coalition of national

governments, individual national governments,

the general public, and private foundations and

The sampling errors for the following demographic subgroup

estimates, in terms of the margin of error at the 95 percent

confidence level, are plus or minus 12 percentage points for

the percentage of those with less than a high school education

who believe research should be done on geoengineering, plus

or minus 13 percentage points for the percentage of blacks

who believe research should be done on geoengineering,

and plus or minus 14 percentage points for the percentage

of Hispanics who believe research should be done on

geoengineering. The margin of error for the remaining

subgroup estimates is plus or minus 9 percentage points.

5 Potential responses to climate

engineering research

GAO-11-71 TECHNOLOGY ASSESSMENT

not-for-profit organizations in making

decisions related to geoengineering.

5.1 Unfamiliarity with

geoengineering

Many people in the United States believe that

Earth is warming but are not certain that this

can be changed, while others do not believe that

global warming is happening (Leiserowitz et al.

2010, 7; Maibach et al. 2009, 1 and 13; Nisbet

and Myers 2007, 451). National surveys of U.S.

public opinion have found broad public support

for a variety of measures to increase energy

efficiency, diversify the energy supply, and

reduce CO

emissions (Pew 2010, 3; Bittle

et al. 2009, 11), but geoengineering has not

yet received widespread attention.

Given the diversity of views on climate change,

our survey asked respondents to consider their

own views on climate change and how serious

climate change might be and to indicate whether

they thought any action should be taken. From

the responses to this question, we estimate that

about 40 percent of the U.S. public thinks that

immediate action on climate change is necessary,

about 35 percent thinks that action should be

taken only after further research, about

10 percent thinks that no action should be

taken, and about 15 percent is unsure. Among

those who do not believe the climate is changing,

we estimate that about 50 percent thinks no

action should be taken and about 40 percent

thinks that action should be taken only after

further research. In other words, members of the

U.S. public who do not believe the climate is

changing do not necessarily oppose research on

climate change.

To ensure that our survey respondents had a basic

understanding of geoengineering, we gave them

a brief definition of geoengineering and examples

of CDR and SRM technologies before we asked

them questions about geoengineering. The

information we gave them was similar in amount

and type to information they might receive in the

nightly news or in a short news article.

Immediately after we defined geoengineering for

our respondents and gave them examples of CDR

and SRM technologies, the survey asked them

whether they had ever heard or read anything

about geoengineering technologies before

they began the survey. From the results, we

estimate that if provided with information about

geoengineering similar to that given our survey

respondents, about 65 percent of the U.S. adult

public would not have recalled hearing or reading

anything about geoengineering technologies at

the time of our survey. The results of our survey

pretest interviews, which included follow-up

questions, indicated that some members of the

public recall reading or hearing about technology

proposals such as sequestration of carbon in the

ocean or other geoengineering-type technologies

in science and technology literature.

Because our focus for this report was on public perceptions

of climate engineering, our survey was not designed to assess

public views of climate change more broadly. It did, however,

ask several questions about climate change and energy policy

similar to those in prior surveys of the U.S. adult population.

While comparisons between our survey and others’ surveys

are not conclusive because of historical, methodological,

and measurement differences, we found a general similarity

between the distribution of our results and those from other

sample surveys.

TECHNOLOGY ASSESSMENT GAO-11-71

5.2 Concern about harm and

openness to research

As identified above, climate engineering

includes a number of technologies, and different

technologies may have different risks and

benefits. To assess whether information about the

potential for harm from different technologies

affects public reaction to climate engineering,

we decided to conduct a split-ballot survey in

which we gave half the sample information about

technologies that had been identified as relatively

safe and the other half information about

technologies that had been identified as less safe.

This allowed us to examine whether receiving

information about the less safe or the more safe

technologies is associated with greater concern

about harm from geoengineering. It also allowed

us to assess whether public opinion on research

and decision making depends on the information

members of the public are given about experts’

assessments of a technology’s relative safety.

We differentiated technologies by the experts’

assessments of safety as described in the Royal

Society report (Royal Society 2009, 6). The two

relatively safe technologies in our survey were

(1) increasing reflection from Earth’s surface (by

painting roofs, roads, and pavement white, for

example) and (2) capturing CO

from the air

(in the information we gave the respondents, we

also called this CO

air capture and capturing

from the air). The two less safe technologies

We did not vary effectiveness in the split-ballot design. In

each ballot group, respondents learned about one technology

that the Royal Society’s 2009 report had identified as highly

effective (either capturing CO

from the air or injecting

stratospheric aerosols) and one that it had identified as

relatively less effective (either increasing reflection from

Earth’s surface or fertilizing the oceans). The design did not

allow us to determine how experts’ assessments of the different

technologies’ effectiveness might affect public reactions to

geoengineering.

were (1) putting sulfates, or tiny mirror-like

particles, into the stratosphere and (2) seeding

large ocean areas with fertilizer. Table 5.1 shows

the information the respondents received about

technology by the ballot group they were assigned

to—506 respondents received information about

increasing reflection from Earth’s surface and

air capture, and 500 received information

about stratospheric sulfates and ocean

fertilization.

We randomly assigned survey respondents to

receive information about the relatively safe

and the less safe technologies. At the outset of

receiving the information about geoengineering,

survey respondents were told that

“Some scientists believe it might be

possible to deliberately change Earth’s

temperature and cool down the planet by

changing some of the things that seem

to be causing global warming. Using

technologies to do this is known

as ‘geoengineering.’

“There are two different types of

geoengineering. The first type involves

reflecting some of the light and heat of

the sun’s radiation back into space. The

second involves reducing the level of

carbon dioxide in the atmosphere.”

The respondents were not aware that the

survey had two different sets of examples of

geoengineering. All the survey questions were

identical.

GAO-11-71 TECHNOLOGY ASSESSMENT

Table 5.1 Geoengineering types and examples given to survey respondents. Source: GAO.

Note: The information provided to respondents was based on a report from the Royal Society (Royal Society 2009).

Example Technology type

Relatively safe (506 respondents) Less safe (500 respondents)

Reflecting back

into space some

light and heat

from the Sun’s

radiation

Increasing reflection from the

surface of Earth

Increasing reflection from the surface

of Earth involves lightening and

brightening the surface of the earth,

to reflect some of the sunlight back

into space. By reflecting sunlight

into space, the temperature would be

reduced. Increasing reflection from

the surface of Earth could involve

painting roofs, roads, and pavement.

Although this should reduce the

temperature at least some, there are

doubts whether reflecting the surface

of Earth could have a substantial

effect on global temperatures. Unlike

some geoengineering techniques,

however, there is little risk of negative

consequences. So the technique of

reflecting the surface of Earth is not

very effective, but it is safe.

Putting sulfates into the stratosphere

Putting sulfates, which are tiny mirror-like particles,

into the stratosphere. This would re-create what

happens when large volcanoes erupt and shoot

sulfates high into the atmosphere. The sulfates

circulate in the stratosphere and reflect some

sunlight before it reaches Earth. Research has

shown that this technique would probably be very

effective at reducing the global temperature. The

extent and type of consequences from stratospheric

sulfates is unknown, however. For example, there

could be increased damage to the ozone layer or

altered rainfall patterns around the world. So the

technique of stratospheric sulfates is likely to be very

effective, but there is also risk of serious negative

consequences.

Reducing carbon

dioxide in the

atmosphere

Capturing carbon dioxide

from the air

air capture would chemically

remove CO

directly from the air.

The CO

could be turned into a

liquid and piped underground for

storage in geologic structures. This

technique directly treats the cause of

climate change—greenhouse gases—

and research has shown that CO

air capture would be very effective.

Unlike some geoengineering

techniques, it would not directly

affect complex natural systems and is

believed to be safe. So the technique

of CO

air capture is likely to be very

effective, and it is safe.

Seeding large ocean areas

with fertilizer

Ocean fertilization involves adding nutrients such

as iron to some areas of the open ocean where they

are in short supply. This promotes the growth of

small plants called phytoplankton, and as the plants

grow, they soak up CO

from the atmosphere.

This technique directly treats the cause of climate

change—greenhouse gas such as CO

. It is not yet

known how much carbon would be removed for

longer than a few years; we need to learn more about

the effectiveness of ocean fertilization. The extent

and type of consequences from fertilizing the oceans

are also largely unknown. For example, there may

be harmful side effects if ocean fertilization were

attempted on a large scale. So the technique of ocean

fertilization may not be very effective and there is

also the risk of serious negative consequences.

TECHNOLOGY ASSESSMENT GAO-11-71

The survey results indicated that some

50 percent or more of both survey ballot

groups were somewhat to extremely concerned

that geoengineering could be harmful. More

specifically, we estimate that

• about 50 percent of the U.S. adult public

would be somewhat to extremely concerned

that geoengineering technologies could

be harmful if they were given information

similar to what we gave the respondents

about relatively safe technologies (increasing

reflection from Earth’s surface and capturing

from the air) and

• about 75 percent of the public would be

somewhat to extremely concerned that

geoengineering technologies could be harmful

if given information similar to what we gave

respondents about less safe technologies

(stratospheric sulfates and ocean fertilization).

These results suggest that many people would be

concerned about the safety of even technologies

that experts have identified as relatively safe.

For technologies experts deemed less safe, a

substantial majority would express concern.

Despite these differences in respondents’

concerns, they did not differ greatly in

their responses to other questions about

geoengineering research and decision making.

Consequently, we report the results from all

other survey questions for all survey respondents

combined.

In addition to the issue of the technologies’ harm,

the survey asked respondents how optimistic

they were that geoengineering technologies could

be beneficial. From the results, we estimate

that about 45 percent of the public would be

somewhat to extremely optimistic, about 40

percent would be slightly to not at all optimistic,

and about 15 percent would be unsure whether

geoengineering technologies could be beneficial.

As reflected in responses to an open-ended

question in our survey, public optimism about

geoengineering is likely to be tempered by

concern that the technologies’ effects are not fully

known. As one survey respondent put it:

“Since the outcome is uncertain, more

research needs to be done to find out

how much of any one thing is enough

or too much.”

Given that research may be seen as a way to

assess whether specific technologies might work

and to identify harmful consequences, we used

the survey to identify a baseline estimate of

support for research on geoengineering among

the U.S. public. From the results, we estimate

that about 65 percent of the public, exposed to

the same type of information as in our survey,

would say they believe that research should

be done to determine whether geoengineering

technologies that deliberately modify the climate

are practical. Further, respondents who received

information about less safe technologies were

just as likely to support research to determine

whether geoengineering is practical as were

respondents who received information about

safer technologies; moreover, about 60 percent

of those who said they were extremely concerned

that geoengineering could be harmful indicated

that research should be done.

The survey respondents’ comments in response

to an open-ended question in our survey illustrate

that research and small-scale testing are seen as

ways to determine whether technologies can be

safely and effectively deployed. In other words,

respondents identified research and small-scale

testing as ways to assess the potential for harm

GAO-11-71 TECHNOLOGY ASSESSMENT

from climate engineering technologies and to

allow for more informed decisions about their use.

The survey results also indicate that while

approximately 65 percent of the public overall

would support research on geoengineering, about

half or more of the U.S. public across a range

of demographic and political groups, including

age, gender, race, ethnicity, education, and

partisanship, would say that research should

be done to determine whether geoengineering

technologies are practical. In other words,

support for research on geoengineering would not

be limited to specific demographic groups.

To explore potential public support for

government-sponsored research on geoengineering,

our survey also asked respondents two separate

questions about whether they would support or

oppose the U.S. government’s paying for research

on CDR or SRM technologies. The responses to

these questions suggest that if public information

were similar to that in our survey, about half the

public would support the U.S. government’s

paying for research on CDR technologies and

about 45 percent would support its paying for

research on SRM technologies.

As we remarked previously, public understanding

of geoengineering is not well developed and

our survey results do not necessarily predict

future views. Furthermore, we did not ask

respondents to consider the trade-offs between

federal financing of geoengineering research and

other possible spending priorities, including

tax cuts or deficit reduction. We also did

not ask respondents whether they supported

private companies’ or other entities’ paying

for research on climate engineering. Support

for the government’s paying for research on

geoengineering technologies could have been

less or more had we asked respondents to choose

alternative policy options or alternative funding

sources. Research funded by a corporation or

foreign government, for example, might yield

different public support.

5.3 Views on climate engineering

in the context of climate

and energy policy

National surveys of U.S. public opinion have

found broad public support for a variety of

measures to increase energy efficiency and

diversify the energy supply (Pew 2010, 3; Bittle

et al. 2009, 11). To place the public’s view of

climate engineering in the broader context of

public opinion on climate and energy policy,

we asked survey questions about reducing CO

emissions by increasing reliance on noncarbon-

based energy sources and other methods in

addition to climate engineering. From the results,

we estimate that about three-quarters of the

public support (strongly support or somewhat

support) developing more fuel-efficient cars,

power plants, and other such technologies;

encouraging businesses to reduce their CO

emissions; and relying more on wind and solar

power (figure 5.1). About 65 percent of the

public strongly or somewhat supports actions to

encourage people to reduce CO

emissions–for

example, by driving less or renovating their

homes. At the same time, our results indicate

that if the public were given the same type of

information as in our survey, about half would

strongly or somewhat support developing

geoengineering technologies. About 45 percent

strongly or somewhat support relying more on

nuclear power.

As the Royal Society reported, concern has

been raised that geoengineering proposals could

reduce public support for mitigating the effects of

TECHNOLOGY ASSESSMENT GAO-11-71

emissions and could divert resources from

adaptation (Royal Society 2009). This is referred

to as the “moral hazard” problem. Given low

public awareness of geoengineering, it is difficult

to determine with any confidence whether the

U.S. public would reduce support for mitigation

as it learned more about geoengineering or how

concerned the public would be about this moral

hazard. Our survey results suggest that if the

public were given the same type of information

about geoengineering as our survey respondents,

it might support a range of approaches to climate

and energy policy, including climate engineering,

rather than viewing different approaches as

trade-offs.

As with the results of qualitative research that

found U.K. public support for combining

geoengineering with mitigation efforts (Ipsos

MORI 2010, 1–2), we found that at least some

of the U.S. public views geoengineering as an

additional method of addressing climate change

rather than as an alternative to mitigation and

adaptation. In open-ended comments, for

example, some respondents expressed support for

using other recognizable means to address climate

1. Developing more fuel-efficient

cars, power plants, and

manufacturing processes to

reduce carbon dioxide emissions

2. Relying more on solar power

3. Encouraging businesses to

reduce their carbon dioxide

emissions

4. Relying more on wind power

5. Encouraging people to drive less,

renovate their houses, and take

other actions to reduce their carbon

dioxide emissions

6. Developing geoengineering

technologies that could cool the

climate or absorb carbon dioxide

from the atmosphere

7. Relying more on nuclear power

Somewhat

support

Neither

support nor

oppose

Somewhat

oppose

Strongly

oppose

Don’t

know

How much, if at all, would you support or oppose each of the following actions?

Strongly

support

Estimated percentage of support or opposition

Survey question:

Figure 5.1 U.S. public support for actions on climate and energy, August 2010. Source: GAO.

Note: Estimates have 95 percent confidence intervals of within plus or minus 4 percentage points.

GAO-11-71 TECHNOLOGY ASSESSMENT

change, such as reducing CO

emissions, and

using geoengineering as a last resort.

5.4 Support for national and

international cooperation

on geoengineering

To obtain baseline information on U.S.

public views on the extent to which different

groups should be involved in deciding to use

a geoengineering technology, our survey asked

respondents how much involvement different

public and private sector groups should have in

making these decisions. From the results of our

survey, we estimate that if the public were given

the same type of information as in our survey, a

total of about 75 percent would support a great

deal, a lot, or a moderate amount of involvement

by the scientific community in making decisions

related to geoengineering (figure 5.2). At the

same time, a total of about 70 percent would

support a great deal, a lot, or a moderate amount

of involvement by a coalition of national

governments; about 65 percent would support

this level of involvement by individual national

governments, the general public, and private

Figure 5.2 U.S. public views on who should decide geoengineering technology’s use, August 2010.

Source: GAO.

Note: Estimates have 95 percent confidence intervals of within plus or minus 4 percentage points.

1. The scientific community

(for example, universities)

2. A coalition of national

governments

3. Individual national

governments

4. The general public

5. Private foundations and

not-for-profit organizations

6. Private, for-profit companies

A lot

A moderate

amount

A little

None

Don’t

know

How much, if any, involvement in decisions to actually use a geoengineering technology on

a broad scale should each of the following groups have?

A great

deal

Estimated percentage of extent of involvement

Survey question:

TECHNOLOGY ASSESSMENT GAO-11-71

foundations and not-for-profit organizations;

and about half would support this level of

involvement by private companies.

To provide additional insight into the U.S.

public’s initial views on actions related to

geoengineering, we asked survey respondents

whether they supported or opposed the U.S.

government’s coordinating more closely with

other countries on geoengineering issues.

We estimate that about 55 percent of the

U.S. public would support the government’s

coordinating more closely with other countries on

geoengineering issues, about 15 percent

would oppose closer coordination, and about

30 percent would be unsure. Overall, the findings

from our survey suggest that if the public were

given similar information about geoengineering,

it would be open to the involvement of multiple

national and international groups. In addition

to expressing support for involvement by a range

of groups in response to closed-ended questions,

survey respondents noted the importance of

involving the scientific community, governments,

the public, and the private sector in making

decisions about geoengineering in their answers

to open-ended questions. In the words of one

respondent,

“national governments, along with the

scientific community, should determine

under what circumstances it would be

okay to actually use geoengineering

technologies.”

GAO-11-71 TECHNOLOGY ASSESSMENT

TECHNOLOGY ASSESSMENT GAO-11-71

In this technology assessment, we have evaluated

climate engineering technologies that could be

part of a portfolio of climate policy options,

along with mitigation and adaptation. We found

that the technologies we reviewed are all in early

stages of development. It is likely that significant

improvements in climate engineering technology

and related information will take decades of

research because (1) today’s technologies are not

mature and (2) data collection and modeling

capabilities related to climate engineering research

are marked by important gaps. Experts have

warned that a delay in starting significant climate

engineering research could mean falling behind

in our capacity to address a potentially damaging

climate trend. We have previously reported that

the United States does not have a coordinated

strategy for climate engineering research.

We cannot ignore the possibility of new risks

from either climate engineering research or its

use or misuse. We found in our survey of U.S.

adults that a majority would be open to climate

engineering research but expressed concern about

possible harm. Likewise, experts who advocate

research emphasized that conducting significant

climate engineering research and using the results

could bring new risks, such as the possibility of

international conflict arising from one nation’s

unilaterally deploying climate engineering

technologies that adversely affect other nations.

Additionally, future technological developments

may bring new and currently unknown risks.

Experts we consulted suggested facilitating

climate engineering researchers’ interactions

with the U.S. public, national decision-makers,

and the international research community.

They also said that international research could

(1) help ensure that the nation is aware of and

keeps pace with others’ research and (2) give

the United States an opportunity to lead by

example by emphasizing transparency in and risk

management for the research. Foresight efforts

concerning emerging trends and technological

developments could help the nation better

anticipate future risks and opportunities.

6 Conclusions

GAO-11-71 TECHNOLOGY ASSESSMENT

TECHNOLOGY ASSESSMENT GAO-11-71

The fifteen experts listed in section 8.7 reviewed a

draft of this report, at our request, and submitted

comments to us. In this section, we summarize

how we addressed the technical and other

comments requiring a response. We also received

a number of positive comments that do not

require a response.

7.1 Our framing of the topic

Some comments pertained to the presentation

of anthropogenic climate change or climate

policy in the introduction to this report.

These comments ranged from objecting to the

presentation of alternative views of climate

change to suggesting that we highlight scientific

consensus on anthropogenic climate change. We

retained information on the range of views as key

introductory content but added a clarification

acknowledging the endorsement of IPCC’s view

by numerous scientific bodies. We also added

a statement linking the large consensus among

authoritative scientific bodies to the sense of

urgency that has contributed to discussions of

engineering the climate. In response to other

comments on the need to emphasize the potential

role of climate engineering as a complement

to mitigation and adaptation, we highlighted

a GAO recommendation that the federal

government develop a coordinated approach to

geoengineering research in the context of a federal

strategy to address climate change (GAO 2010a).

We also incorporated suggestions to balance

the risks introduced by engineering the climate

against the risks of climate change without

climate engineering.

7.2 Our assessment of

technologies

Several comments surrounded the scope of the

criteria we used to assess climate engineering

technologies. Many of these comments concerned

the appropriateness of TRLs to measure the

readiness of soft climate engineering technologies

for deployment, as opposed to devices or

hard technologies. Given these comments, we

discussed a key limitation of TRLs—that is,

their sensitivity to certain criteria, such as the

definition of a system concept or concrete plan.

Developing an alternative way to measure the

maturity of technologies was beyond our scope.

In response to comments on the other key

measurements, we revised the draft to emphasize

the potential effectiveness and potential

consequences of the technologies we assessed.

To address concerns about the precision of cost

estimates from the scientific literature, we focused

on cost factors, or resources required to develop

or deploy climate engineering technologies.

Finally, we revised tables 3.1 and 3.2 to reflect

these amplifications and clarifications.

7.3 Our assessment of

knowledge and tools

for understanding

climate engineering

To incorporate comments on the status of

knowledge and tools for understanding climate

engineering, we reemphasized our focus on the

value of research to help improve climate science,

observational systems, or computing power. We

replaced generalizations with examples of areas

7 Experts’ review of a draft of this report

GAO-11-71 TECHNOLOGY ASSESSMENT

that scientists have targeted for improvements,

and we strengthened our citations. We added

climate chemistry models to our taxonomy

of existing climate models. We updated some

examples, such as NASA’s CLARREO mission.

We also accepted editorial comments clarifying

certain ideas. For example, we characterized

scientists’ concerns about the reliability of

observational networks in terms of the continuity

of the observational record, and we revised the

text to highlight the potential value of developing

high-performance computing resources that

could be dedicated to resolving uncertainties

about regional climate variables. Although

some comments noted that various observations

could apply to other areas of climate science, we

considered these comments to be beyond

the scope of our report. Comments on

decision-making under uncertainty were also

beyond our scope.

7.4 Our foresight and survey

methodologies

Comments on foresight and survey

methodologies centered on the rationale for the

content of the events described in the scenarios

and the survey questions. In the foresight section

of this report, the experts’ views on the future

are not based primarily on events described in

the scenarios. Rather, the scenarios led a wide

range of experts to share their views on the

future of climate engineering research over the

next 20 years (section 8.1.2), thus allowing a

broad thematic discussion of these views, which

sometimes differed sharply. The scenarios

reflect the views of the experts who helped build

them, but our overall foresight approach gave

considerable latitude to the expression of views

by all experts we consulted. Additionally, we

included experts with many different kinds of

expertise and varied views on climate engineering.

For these reasons, we are confident that our

overall results would have been similar had the

scenarios differed or been produced on the basis

of an explicit underlying rationale.

Objectives for the survey included developing

baseline information on public awareness of

climate engineering technologies, views about

research on them, and opinions on who should

be involved in decisions related to climate

engineering. Our focus groups and pretest

interviews indicated that members of the public

were unlikely to have either detailed knowledge

or established opinions about climate engineering

and that public views on climate engineering

depended on the technology. Therefore, we

developed and pretested (1) a basic definition of

climate engineering with examples of different

technologies, in both audio-visual and written

formats so respondents could choose between the

two, and (2) basic survey questions about

each respondent’s awareness of and views on

research and groups that should be involved in

decisions. Our pretest results led us to believe

that the respondents understood the basic

questions and that these were unbiased and

provided the baseline information we needed

to meet our objectives.

We did not incorporate other suggestions that

were beyond the scope of our report. It was,

for example, as much beyond our scope to

develop a detailed strategy for deploying climate

engineering as to compare a climate-engineered

world with one lacking any deliberate climate

intervention.

TECHNOLOGY ASSESSMENT GAO-11-71

8.1 Objectives, scope,

and methodology

In this appendix, we describe the several targeted,

coordinated methods we used to report on

• the current state of climate engineering

technology,

• experts’ views of the future of climate

engineering research, and

• public perceptions of climate engineering.

In addition to the separate methods we used

to address each objective, with the assistance

of the National Academy of Sciences (NAS)

we convened a meeting of scientists, engineers,

and other experts that we called the Meeting

on Climate Engineering. Because climate

engineering is complex, NAS selected, with

our assistance, a diverse and balanced group

of experts on climate engineering, climate

science, measurement sciences, foresight studies,

emerging technologies, research strategies, and

the international, public opinion, and public

engagement dimensions of climate engineering.

Experts participating in our Meeting on Climate

Engineering are listed in section 8.6.

Before meeting in Washington, D.C., on

October 6–7, 2010, the participants were

provided with a written summary of our progress

on this technology assessment. We explained to

the participants that the summary was a working

document showing what we had developed up to

that point and that it did not fully describe our

methodology.

The participants were organized into subgroups

to focus on the major topics of our technology

assessment, including carbon dioxide

removal (CDR) technologies, solar radiation

management (SRM) technologies, the future

of climate engineering, and public perceptions.

The participants in each subgroup presented

a 5-minute summary of their views on our

preliminary findings, and then the entire group

discussed the feedback. The meeting ended with

general reactions to and advice and suggestions

on our preliminary findings.

The participants’ comments led us to review

additional literature and unpublished studies

that they suggested. Following the meeting, we

also contacted the participants in person or by

telephone or e-mail to clarify and expand what

we had heard. We used what we learned from

this meeting of experts to update, clarify, and

correct where appropriate our information on the

current state of climate engineering technology,

expert views of the future of climate engineering

research, and public perceptions of climate

engineering. We incorporated in our draft report

the lessons we learned from the meeting to give it

greater accuracy and contextual sophistication.

8.1.1 Our method for assessing the

state of climate engineering

technology

To determine the current state of the science and

technology of climate engineering, we reviewed

a broad range of scientific and engineering

literature. We started with the literature the

Royal Society report referenced (Royal Society

2009, 63–68), and then we reviewed the

literature we found in NAS, National Research

Council (NRC), and U.S. government reports

on climate change. We identified other literature

8 Appendices

GAO-11-71 TECHNOLOGY ASSESSMENT

from scientific and climate-related organizations

such as the National Aeronautics and Space

Administration (NASA) and National Oceanic

and Atmospheric Administration (NOAA), and

we reviewed proceedings from conferences such

as the 2010 Asilomar International Conference

on Climate Intervention Technologies (Asilomar

Scientific Organizing Committee 2010). We

revisited the report on climate engineering that

we issued in September 2010 (GAO 2010a),

which is complementary to this report. We

reviewed relevant congressional testimony. We

sought additional literature from the experts we

spoke with.

We identified experts on climate engineering

and proponents of specific climate change

technologies from our review of the literature

and conference proceedings. To ensure balance

across the views and information we obtained, we

interviewed a broad range of experts and officials

working in climate science research and climate

engineering whose track records had been proven

through their peer-reviewed publications and

presentations at conferences. We interviewed

these experts to seek information that was not in

their published work. We interviewed scientists,

engineers, and knowledgeable officials with the

Department of Energy’s (DOE) National Energy

Technology Laboratory (NETL), Lawrence

Livermore National Laboratory, and Pacific

Northwest National Laboratory (PNNL) and

during site visits conducted at

• the National Center for Atmospheric Research,

• the National Oceanographic and Atmospheric

Administration’s Earth System Research

Laboratory,

• the National Institute of Standards and

Technology,

• Oak Ridge National Laboratory,

• American Electric Power’s Mountaineer

Power Plant in West Virginia,

• the Institute for Advanced Study at

Princeton University,

• the Marine Biological Laboratory at

Woods Hole,

• Scripps Institution of Oceanography, and

• Woods Hole Oceanographic Institution.

We interviewed selected attendees at the 2010

Asilomar International Conference on Climate

Intervention Technologies.

We reviewed records of earlier interviews we had

conducted on topics relevant to this technology

assessment. We analyzed interviews with high-

level private-sector officials from

• Alstom, which develops carbon capture

technology and equipment;

• Dow, which conducts research on and

development and manufacture of solvents or

sorbents needed for CO

capture; and

• Schlumberger Carbon Services, which engages

in geological mapping and the characterization

of subterranean structures for storing CO

We interviewed experts at academic institutions

such as Columbia University, the Massachusetts

Institute of Technology, and Stanford University.

Because climate science and climate engineering

are interdisciplinary and extremely complex,

with cross-cutting issues that may be beyond any

one expert’s realm, we synthesized information

from an array of experts with diverse views on

TECHNOLOGY ASSESSMENT GAO-11-71

these subjects. We did not try to interview an

equal number with alternative perspectives on

all issues or technologies, because we were not

evaluating the information we gathered by the

number of experts who mentioned a topic or

stated a particular view. Our objectives were

to identify experts’ (1) general understanding

of the current state of climate science and

engineering and (2) their major uncertainties

and outstanding issues on these subjects. We

did not attempt to determine the independence

of individual experts, but we did try to obtain

a balanced set of views. We wanted to obtain a

broad perspective on the current state of climate

science and engineering and objectively report

this information. The experts we spoke with are

listed in section 8.2.

We used the Royal Society’s classification of

climate engineering approaches to focus our

review on CDR and SRM technologies (Royal

Society 2009, l). We did not include climate

engineering approaches that address other,

non-CO

greenhouse gas emissions such as

nitrous oxide. After consulting with experts, we

limited our assessment of climate engineering

technologies to those the Royal Society addressed

in its 2009 report. Of those technologies, we did

not assess ocean reflectivity or ocean upwelling

or downwelling because we found limited

information on them in the peer-reviewed

literature. We also did not assess research on the

possible causes of climate change.

We assessed and described the current status

of climate engineering technologies along four

key dimensions: (1) maturity, (2) potential

effectiveness, (3) cost factors, and (4) potential

consequences. We assessed the maturity of

climate engineering technologies by their

technology readiness levels (TRL)

(table 8.1). TRLs are a standard tool for

assessing the readiness of an emerging

technology for production or incorporation

into an existing technology or system. The

Department of Defense and NASA use TRLs,

as does the European Space Agency.

We used the AFRL (Air Force Research

Laboratory) Technology Readiness Level

Calculator Version 2.2 (Nolte 2004) to

determine technology readiness levels for the

climate engineering technologies we reviewed.

Table 8.1 summarizes key features of TRL

ratings. The first column presents definitions of

TRL levels used as “Top Level Views” in the TRL

calculator. The calculator operates conditionally:

to achieve a rating at any level, a technology must

satisfy the requirements for all lower levels as

well. For example, to achieve a rating of TRL 2, a

technology must also satisfy the requirements for

a rating of TRL 1. To achieve a rating of TRL 3,

a technology must also satisfy the requirements

for a rating of TRL 2, and thus must also satisfy

the requirements for a rating of TRL 1.

We developed criteria to rate climate engineering

technologies using the TRL calculator. For the

top level view of TRL 1, requiring that basic

principles be observed and reported, we asked

whether the technology had been described as a

climate engineering technology in peer-reviewed

scientific literature. All the climate engineering

technologies we reviewed met this condition.

For the top level view of TRL 2, requiring

the formulation of a technology concept or

application, we asked whether a system concept

identifying key elements of the technology or a

concrete plan existed for implementation on a

global scale. Some technologies failed to meet this

condition for climate engineering even though

they would be fully mature in other applications.

For example, increasing the reflectivity of settled

GAO-11-71 TECHNOLOGY ASSESSMENT

Level Description Example

1 Basic principles have been

observed and reported

The lowest level of technology

readiness. Scientific research begins

translation into applied research

and development

Paper studies of the

technology’s basic

properties

2 Technology concept or

application has been

formulated

Invention begins. Once basic

principles are observed, practical

applications can be invented. The

application is speculative, and no

proof or detailed analysis supports

the assumption

Limited to paper studies

3 Analytical and

experimental

critical function or

characteristic proof of

concept has been defined

Active research and development

(R&D) begins. Includes analytical

and laboratory studies to physically

validate analytical predictions of

separate elements of the technology

Components that are

not yet integrated or

representative

4 Component or

breadboard validation

has been made in

laboratory environment

Basic technological components

are integrated to establish that the

pieces will work together. This is

relatively “low fidelity” compared

to the eventual system

Ad hoc hardware

integrated in a laboratory

5 Component or

breadboard validation

has been made in

relevant environment

Fidelity of breadboard technology

increases significantly. The

basic technological components

are integrated with reasonably

realistic supporting elements so

the technology can be tested in a

simulated environment

“High fidelity”

laboratory integration

of components

6 System and subsystem

model or prototype has

been demonstrated in a

relevant environment

Representative model or prototype

system is well beyond level 5

testing in a relevant environment.

Represents a major step up in

the technology’s demonstrated

readiness

Prototype tested in a

high-fidelity laboratory

or simulated operational

environment

7 System prototype has

been demonstrated in an

operational environment

A prototype is operational or nearly

operational. Represents a major

step up from level 6, requiring

the demonstration of an actual

system prototype in an operational

environment, such as in an aircraft,

vehicle, or space

Prototype tested in a

test bed aircraft

Table 8.1 Nine technology readiness levels, continues on next page

TECHNOLOGY ASSESSMENT GAO-11-71

areas by painting rooftops white would be mature

on a small scale but lacked a system concept and

a concrete plan for implementation on a global

scale. Since this technology failed to meet the

condition for TRL 2, it was rated at TRL 1. The

sensitivity of the TRL ratings to the definition of

a system concept or a concrete plan for climate

engineering is a key limitation of using TRLs to

evaluate technologies that are otherwise mature.

For the top level view of TRL 3, requiring

analytical and experimental demonstration

of proof of concept, we looked for significant

experimental data on elements of the technology.

For example, a technology designed to reduce

solar radiation by placing scatterers at L1

fulfilled the basic requirements for TRL 2 but

not TRL 3 because the supporting literature was

theoretical and did not provide experimental

data. Finally, for the top level view of TRL 4,

requiring technological demonstration, we looked

for evidence of system demonstration with a

breadboard unit (a representation of the system,

in function only, used to determine feasibility

and to develop data, configured for laboratory

use). Because none of the technologies that we

reviewed had system data with breadboard units,

none could be rated at TRL 4 or higher.

We had earlier recommended that a technology

should be at level 7—that is, a prototype

has been demonstrated in an operational

environment—before being moved to

engineering and manufacturing development.

We had recommended further that a technology

be at level 6 before starting program definition

and risk reduction (GAO 1999). We characterize

technologies whose TRL scores are below 6

as “immature.”

Two factors that affect global temperature are

(1) the level of CO

and other greenhouse gases

in the atmosphere and (2) the amount of solar

radiation that Earth and its atmosphere absorb.

Level Description Example

8 Actual system is complete

and has been qualified

in testing and

demonstration

Technology has been proven to

work in its final form and under

expected conditions. In almost all

cases, this level represents the end

of true system development

Developmental test and

evaluation of the system

to determine if it meets

design specifications

9 Actual system has been

proven in successful

mission operations

The technology is applied in its

final form and under mission

conditions, such as those

encountered in operational test and

evaluation. In almost all cases, this

is the end of the last “bug fixing”

aspects of true system development

The system is used in

operational mission

conditions

Table 8.1 Nine technology readiness levels described. Source: GAO based on Nolte (2004).

Note: A breadboard is a representation of a system that can be used to determine concept feasibility and

develop technical data. It is typically configured for laboratory use only. It may resemble the system in function only.

GAO-11-71 TECHNOLOGY ASSESSMENT

Because CDR and SRM affect temperature

in different ways, their effects are measured

differently. CDR removes CO

from the

atmosphere while SRM reduces the amount of

solar radiation that Earth and its atmosphere

absorb—by reflecting the radiation into space

before it reaches Earth’s atmosphere, when it

reaches Earth’s atmosphere, or when it reaches

Earth’s surface.

To describe the effectiveness of proposed CDR

technologies, we examined the Royal Society’s

qualitative ratings of various technologies’

effectiveness (high, medium, and low). We also

examined two quantitative measures reported

in the literature: the estimated (1) maximum

reduction of the atmospheric concentration of

(ppm) from its projected level of 500 ppm

in 2100 and (2) annual ability to remove CO

from Earth’s atmosphere (gigatons of CO

per

year) when compared to annual anthropogenic

emissions of 33 gigatons of CO

We assessed

the qualitative ratings primarily by making

• a check for reasonableness. For example, for

bioenergy with CO

capture and sequestration

(BECS) the Royal Society reported an

anticipated maximum CO

reduction ability

of between 50 ppm and 150 ppm and rated

BECS as low to medium in effectiveness.

We confirmed the reasonableness of rating

a reduction of 150 ppm as having medium

effectiveness by noting that this level of

reduction would put the concentration of CO

in the year 2100 at 350 ppm—which is below

the current 390 ppm but does not approach

the preindustrial 280 ppm.

The preindustrial CO

concentration is reported to have been

280 ppm. In 2010, the atmospheric concentration of CO

was

estimated in the literature as 390 ppm. In the year 2100, the

concentration projected for a mitigation scenario is 500 ppm.

• comparisons to other scientific sources.

We reviewed scientific literature for other

assessments indicating the overall feasibility

of implementing individual CDR technologies

on a global scale to achieve a net reduction

of atmospheric CO

concentration. For two

technologies—direct air capture of CO

with geologic sequestration and enhanced

weathering—sources in the peer-reviewed

literature provided views or information

that differed substantially from the Royal

Society’s ratings.

Overall, for three of the six CDR technologies,

our assessments confirmed the specific Royal

Society qualitative effectiveness ratings. We

included these three Royal Society ratings in the

“potential effectiveness” column in table 3.1. For

one other technology (land use management),

which the Royal Society rated as low, other

scientific literature suggested a low to medium

rating, which is reflected in table 3.1. For the

remaining two CDR technologies (direct air

capture of CO

with sequestration, and enhanced

weathering), we did not report an overall

qualitative rating for potential effectiveness; that

is, we indicated “not rated” because sources in

the scientific literature provided information that

differed considerably from the Royal Society’s

ratings. However, where possible, we provided

other relevant information.

To describe the potential effectiveness of SRM

technologies, we used the generally accepted

benchmark of the climate change community

(such as in the work of the Intergovernmental

Panel on Climate Change (IPCC)) called

The high effectiveness rating the Royal Society gave for

these two technologies could not be confirmed and validated

by reports in the literature. We did not assign an overall

qualitative rating to these technologies because of conflicting

indications in the literature about their effectiveness.

TECHNOLOGY ASSESSMENT GAO-11-71

equilibrium climate sensitivity.

Climate

modeling studies use equilibrium climate

sensitivity as a benchmark to indicate the effect

of greenhouse gases on the climate. Equilibrium

climate sensitivity is defined as the change in

global mean surface temperature following

warming caused by a doubling of preindustrial

levels (Solomon et al. 2007). The doubling

of preindustrial CO

levels is also used in

modeling studies as a standard condition for

evaluating climate effects other than an increase

in global average temperature. Following this

approach, the climate engineering community

evaluates the effects of SRM technologies against

double preindustrial CO

levels. We described

the potential effectiveness of SRM technologies

when fully implemented on a global scale,

based on the extent to which they are estimated

to reduce global average surface temperature

compared to the benchmark. We categorized the

potential effectiveness of each climate engineering

technology as a percentage, where 100 percent

is anticipated to lower global mean temperature

from the benchmark to the preindustrial value

and is termed “fully effective.”

We did not assess the effectiveness of either

deploying multiple climate engineering

technologies simultaneously or combining them

with reductions in carbon emissions and advances

in energy technology. We did not assess the

effectiveness of deploying a technology in any

specific place. Because we focused on global mean

surface temperature, we did not assess specific

geographic temperatures or climate changes.

We did not independently determine the costs

of implementing the technologies. Instead,

we report cost factors and estimates from the

The word “equilibrium” indicates a steady state response to

specify climatic conditions, such as the concentration of CO

and variables related to climate engineering.

literature we reviewed; these are based on ideas

of what the technologies might be, not on

detailed design and schedule data. For CDR,

the cost factors represent resources used to

remove CO

from the atmosphere and store it;

when quantified, these are presented on a per

ton basis. For SRM, the cost factors represent

resources required to counteract global warming

from doubling the preindustrial atmospheric

concentration of CO

, or, for technologies that

are not anticipated to be fully effective, the

resources required to counteract warming to the

maximum extent possible. We were not able

to determine the reliability of estimated costs

in the literature because of insufficient data

or inadequate descriptions of how costs were

determined.

We assessed the potential consequences of each

technology by summarizing risks or consequences

identified in the literature, modeling studies, and

our interviews with experts. We also reviewed

congressional hearings for the testimony of

experts who presented risks of implementing

specific technologies. We reviewed the ability

of existing climate models to represent climate

processes expected to result from climate

engineering technologies, including altered

wind currents, rain patterns, and ocean

temperatures. We considered the ability to

reverse a technology’s deployment as a type of

consequence.

To report on the status of knowledge and tools

for understanding climate engineering, we

reviewed relevant literature and interviewed

scientists and other experts about climate science,

observational networks, and computing resources.

Our literature review included GAO publications

as well as reports from the Department of Energy,

Intergovernmental Panel on Climate Change,

National Aeronautics and Space Administration,

GAO-11-71 TECHNOLOGY ASSESSMENT

National Institute of Standards and Technology,

National Oceanic and Atmospheric

Administration, National Research Council,

United States Climate Change Science Program,

and World Climate Change Programme, in

addition to peer-reviewed scientific literature.

Because we found few studies focusing on

climate engineering modeling or research, we

included in our review some studies of climate

models and science that are relevant to climate

engineering. Our research on observational

systems focused on the coverage, continuity, and

accuracy of networks collecting measurements

related to substances or processes that are

important to climate engineering. Similarly, our

examination of computing resources focused on

current limitations or potential improvements

that could affect climate engineering research,

such as the spatial resolution of computations

in current models. We did not independently

evaluate whether scientific knowledge or tools

are sufficiently well understood or developed for

making decisions about the possible development

or use of climate engineering technologies. We

also did not assess whether climate change is

occurring or what is causing any climate change

if it is occurring or whether current scientific

knowledge supports the occurrence of climate

change or its causes.

8.1.2 Our method for eliciting experts’

views of the future of climate

engineering research

To assess how climate engineering research might

develop in the future, we used the following

three sources: (1) a foresight exercise in which

experts developed alternative scenarios, (2) the

comments of a broad array of experts stimulated

by the scenarios, and (3) additional views of

other experts in response to our preliminary

synthesis developed from the scenarios and

earlier comments. Sections 8.4 to 8.6 list the

experts we consulted in developing each of these

sources.

We present our summary of the three

sources in the body of our report to suggest some

possibilities for climate engineering research over

the next 20 years.

All experts we selected to participate in the

foresight exercise and to comment in response

to the scenarios met at least one of the following

criteria: they (1) held a position in a university or

other well-known organization relevant to climate

engineering, climate change, or related topics;

(2) had participated in academic or professional

panels addressing climate engineering, climate

change, or related topics; or (3) had authored

peer-reviewed publications on climate

engineering, climate change, or related topics.

8.1.2.1 Scenario-building process

A meeting to build scenarios held on

July 27, 2010, at GAO headquarters was

facilitated by a professional from the Institute

for Alternative Futures. The overall goal of

the exercise was to develop four scenarios to

illustrate alternative possible futures for climate

engineering research, including the amounts and

kinds of research that might be conducted on

CDR and SRM and whether significant progress

was expected.

The scenario-builders (listed in section 8.4) were

selected to constitute, as a group,

• expertise on specific technologies for

engineering the climate, including CDR

and SRM, and experience in the research or

development of relevant technologies;

Additionally, in preparing for these activities we interviewed

other experts who provided background information or

recommended some of the experts listed in sections 8.4 to 8.6.

TECHNOLOGY ASSESSMENT GAO-11-71

• knowledge on climate engineering as well

as the development of future-oriented

scenarios, including foresight about emerging

technologies and national and international

approaches to them; and

• collective backgrounds in private industry,

government (including the military), and other

organizations such as those in academia.

We selected six external scenario-builders. Each

of the six was a leading expert in one or more key

fields or had been recommended to us by other

experts. The group’s knowledge and expertise

represented a balance across the items bulleted

above and spanned energy policy, climate

change, oceanography, atmospheric science,

and biotechnology, as well as research on CDR

and SRM and other areas, such as foresight

and public engagement. Timothy Persons,

GAO’s Chief Scientist, served as the host and

ex-officio member of the group to help guide

the discussion.

To build the four scenarios, we began by

reviewing scientific and engineering literature

and interviewing scientists and engineers to help

us identify what were likely to be the key factors

in the future scope and direction of climate

engineering research in the United States. We

used this information to construct a questionnaire

that we sent by e-mail before the meeting to the

six external experts and GAO’s Chief Scientist.

Before the scenario-builders met on July 27,

2010, they responded individually to our e-mail

questionnaire. The questionnaire asked for their

opinions on the goals of climate engineering

research, the importance of making substantial

progress toward those goals by 2030, the promise

of different approaches toward reaching the

goals, the research that might appropriately be

supported by private or government funds, any

leadership the federal government should take

on climate engineering research, the need for

international cooperation, the likelihood of future

climate changes, and the moral hazard if climate

engineering research looked as if it were headed

on an efficient and effective course. We also asked

for separate answers to these questions as they

related expressly to CDR and SRM technologies.

The questionnaire also listed various factors

that might affect climate engineering research

and asked for the scenario-builders’ opinions on

these and other relevant factors. The answers

we received suggested the importance of

factors subsequently selected for the meeting’s

discussion. For example, five of the six scenario-

builders responded that government incentives to

industry would make the prospect of achieving

some or all CDR research goals by 2030 “highly

promising.” We provided them with a summary

of their answers to the questionnaire at the outset

of the scenario-building meeting.

During the meeting, the scenario-builders

identified and discussed many kinds of factors

important for future U.S. climate engineering

research in a global context. They selected

two policy-related factors as potentially most

significant. One was whether a federal research

program on CDR and SRM would be established

and, if so, at what level (the scenario-builders

did not focus on low-risk SRM methods such

as whitening roofs and roads). The scenario-

builders discussed a broad definition of a research

program that might include related activities,

such as engaging the public or encouraging

industry to implement technology-related

results (including improving opportunities for

dissemination). The other policy factor was

whether carbon constraints would be established

and, if so, at what level in the United States and

internationally.

GAO-11-71 TECHNOLOGY ASSESSMENT

The scenario-builders discussed how carbon

constraints can take the form of either emissions

pricing or regulations designed to reduce

carbon emissions. After selecting the two

factors—a federal research program and carbon

constraints—the scenario-builders specified three

levels for each one, defining nine combinations,

each of which might serve as the basis for a

scenario (figure 8.1). From the nine possible

combinations, the scenario-builders selected for

further consideration the four combinations

labeled on figure 8.1. The four resulting scenarios

define a range of futures within the bounds set by

variation across the two selected factors.

Each scenario was developed separately for

a specific combination of factors. However,

a logical inference is that more pathways are

possible within the range defined by the two

factors because of the possibility of transitions

from one scenario to another. Scenario II, for

example, could overlap with Scenario IV. The

purpose of the scenarios was to stimulate thinking

about the future, not to limit anticipation to any

one cell.

We asked the scenario-builders to identify

low-probability high-impact events such as “black

swans” and “black pearls.” We defined black swan

as an extremely unlikely event able to produce

catastrophic or otherwise large effects. We

defined black pearl as a black swan with positive

effects. We generated this list to help identify

wild cards or conditions that could drastically

change the future as related to the climate and

climate engineering research.

Toward the end of the scenario-building meeting,

we asked the six external scenario-builders to

look ahead to 2030 and beyond and to consider

possible outcomes linked to research on CDR

and SRM. We asked them to assess, subjectively

and qualitatively, three potential future

Level of constraint on carbon

Low or none

Medium

High

Scenario IV

Scenario I

Scenario II

Scenario III

High

Medium

Low or none

Relative level of federal research program

(climate engineering) and related activities

Status quo on both

Some action on both

More action on both

Action on

research only

Figure 8.1 Four scenarios defining alternative possible futures. Source: GAO.

TECHNOLOGY ASSESSMENT GAO-11-71

situations that might occur in or after 2030:

(1) an emergency in which decision-makers

might consider using SRM, (2) continued

global warming, and (3) a future with no

further warming.

8.1.2.2 Experts’ comments

stimulated by scenarios

We used the scenarios to elicit additional views

about the future from 28 experts (listed in

section 8.5) who represented a wider range of

backgrounds and perspectives. To help ensure

balance in the wider group of experts who

would review and respond to the scenarios, we

specifically selected some experts with competing

views and different backgrounds. These experts

were thus characterized by

• varied backgrounds (including, for example,

economics, ethics, the humanities, and

international relations);

• a range of organizational affiliations

(including universities, the public sector, the

private sector, and advocacy groups or other

organizations associated with a viewpoint); and

• differing perspectives (including some known

to favor or oppose the development of climate

engineering technologies or to have expressed

uncertainty about climate change trends).

In August 2010, we e-mailed the four scenarios

to the selected 28 experts along with a brief

questionnaire on their reactions to the scenarios.

We invited them to provide alternative mini

scenarios or other statements of their views

about the future. We asked them to identify

black swans and black pearls. We also asked

them for any message about the future of

climate engineering research and its consequent

risks that they believed would be important

for policymakers to consider. Not all expressed

views on all issues. We followed up with e-mail

questions for clarification, as needed. In a

few instances, we followed up with telephone

conversations or met in person with experts who

were available in the Washington, D.C., area. We

synthesized the varied responses we received from

the experts.

8.1.2.3 Experts’ views of our initial

synthesis and preliminary findings

As we described above, we convened with NAS’s

help a meeting of scientists, engineers, and

other experts. For this meeting, we presented

information about the scenarios and asked the

experts to discuss our preliminary findings about

views expressed regarding the future and to share

their own views about the future. Some experts

did not express views on the scenarios or all

topics discussed.

8.1.2.4 Our analysis: A qualitative

foresight synthesis

We call our summary of the combined results

of the exercises we have described a qualitative

foresight synthesis. The summary is primarily

based not on how many experts made specific

comments or any number of votes taken of the

experts but, rather, on a qualitative approach in

which we identified recurring, prominent themes

and used professional judgment. The summary

is a synthesis of views from a diverse range of

experts and from three interconnected foresight

exercises. It is the result of an iterative process

whereby one set of experts developed scenarios,

another set commented on those scenarios, and

a third set reviewed our initial synthesis of the

first two exercises. In areas where either a clear

majority of the experts we consulted agreed or

only a small number took a specific position, we

say that a “majority” expressed the position or

GAO-11-71 TECHNOLOGY ASSESSMENT

that a small number stated a concern. However,

for transparency, footnotes provide information

on specific counts of experts we consulted who

voiced key opinions.

Although the experts we consulted do not

necessarily represent the views of all those

with similar expertise in the area of climate

engineering, because of the three-stage process

and the breadth of experts we consulted, we

believe that the resulting overall set of views

about the future that we present in section 4

of this report (“Experts’ Views of the Future of

Climate Engineering Research”) would be similar

even if we had used a different set of scenarios

or if we had consulted with a different but still

diverse set of experts.

8.1.3 Our method for assessing

potential responses to

climate engineering

To gather information about public awareness

of and views on geoengineering technologies,

we reviewed selected survey research on public

opinion on climate change, conducted focus

groups, and contracted with Knowledge

Networks Inc. to use its online research panel

to field a survey we developed. The survey was

fielded from July 19 to August 5, 2010. Of a total

sample of 1,623 U.S. residents 18 years old and

older, 1,006 completed the survey.

From our review of the research on climate

engineering and survey research on climate

change, we did not expect the focus group

participants or survey respondents to know very

much about climate engineering technologies.

Therefore, before asking questions about

geoengineering, we gave the focus group

participants and the survey respondents a

basic definition of geoengineering, described

the differences between CDR and SRM,

and provided examples of both. The level of

information we gave the focus group participants

and survey respondents was comparable to

what average adults exposed to news media

descriptions of these technologies might be

expected to receive.

To help us develop the protocol for the focus

group with members of the public and to

increase our understanding of public perceptions

of climate change and climate engineering,

we conducted four focus groups with GAO

employees. We used what we learned from these

focus groups to make changes to the protocol

for the public focus group.

We selected the

11 members of the public focus group for their

diversity in age, gender, race, ethnicity, and

education. Some participants spoke both English

and Spanish; they translated for one participant

who was fluent only in Spanish. A GAO analyst

fluent in English and Spanish observed the

focus group.

We first asked the focus group participants

to discuss their beliefs about climate change,

including whether they believed the climate is

changing and, if so, what the cause is. We then

asked them if they thought there was anything

they personally could do to affect climate change

and what, if anything, the public, industry,

government, or scientists and engineers should

do with respect to climate change. Participants

identified personal actions such as driving

less, using alternative fuels, and writing letters

to influence elected representatives. With

respect to government, industry, and scientists

We also conducted two focus groups with science and

engineering graduate students participating in Arizona State

University’s Consortium for Science, Policy & Outcomes

(CSPO), one before and one after the public focus group. We

did not make any changes to the focus group protocol as a

result of the CSPO focus group conducted before the public

focus group.

TECHNOLOGY ASSESSMENT GAO-11-71

and engineers, participants thought greater

enforcement of existing laws, the provision of

government incentives to address climate change,

and increased public education about climate

change were ways to address climate change.

When asked whether they were aware of any

scientific or engineering solutions to climate

change, focus group participants did not identify

any specific solutions. One participant stated that

scientists and engineers might develop solutions

to climate change but that money is not being

directed to this.

After asking focus group participants if they

were aware of any scientific or technological

solutions to climate change, we explained what

geoengineering is and gave them information

about three different technologies, including

CDR and SRM technologies. We asked

participants to discuss their reactions to each

technology and whether they supported or

opposed it. In addition, we asked them to

discuss how the federal government, industry,

and individuals should fund and make decisions

about geoengineering.

We chose to use “geoengineering” in the

information we gave the focus group and survey

participants, given that we and others, such as

the Royal Society, had used this term earlier.

In our focus groups, we found that participants

raised concerns about the potential for harm

from geoengineering technologies and reacted

differently to different technologies. For example,

one participant, asked to react to information

about stratospheric sulfates, expressed the view

that dinosaurs had become extinct by the Sun’s

having been blocked. Another, reacting to the

concept of direct air capture, expressed concern

about the long-term storage of CO

To assess whether these differences in reaction

to different technologies exist also in the larger

population, we administered a split-ballot survey.

Using experts’ assessments of safety described

in the Royal Society report on geoengineering,

we gave half the respondents information about

technologies (one CDR and one SRM) that

experts identified as relatively safe, and we gave

the other half information about technologies

(one CDR and one SRM) that experts identified

as relatively less safe. We included a question in

the survey to assess whether this difference in

information about experts’ assessment of safety

affected participants’ perceptions of potential

harm from CDR and SRM technologies. We also

examined whether views about geoengineering

research, development, and decision-making

were affected by learning about more or less safe

technologies. Our survey results indicated that

respondents differed in their level of concern

about harm from geoengineering, depending on

whether they received information about more

or less safe technologies, but they did not differ

greatly in their responses to other questions about

geoengineering research and decision-making.

Consequently, we report the results from all other

survey questions combined.

The respondents could choose one or more of

three ways to receive information about different

types of geoengineering technologies: they

could (1) view a video and listen to a narration,

(2) listen to the narration, or (3) read printed

information. All survey questions were identical

in the two survey ballot groups.

Every survey introduces sampling and

nonsampling errors, including errors of

processing, measurement, coverage, and

nonresponse. We took steps to reduce such

errors. To reduce processing error, we verified

all computer programming and analyses

independently. To reduce measurement error,

we conducted 11 pretests with persons of

GAO-11-71 TECHNOLOGY ASSESSMENT

varied education, income, English proficiency,

age, gender, and race.

The pretests included

face-to-face interviews using the draft written

survey as well as telephone interviews with

those completing the web version of the survey.

From the pretest results, we made a number of

changes to reduce the likelihood of measurement

error from respondents’ misunderstanding or

misinterpreting the survey questions. We also

asked all pretest respondents whether any specific

questions or the survey overall was biased in

any way, and we made changes to address the

concerns they raised. Knowledge Networks’

online research panel was designed to minimize

errors of coverage of the target population of

U.S. adults. The sample frame was based on

probability sampling that covered both people

who had home access to the Internet and those

who did not. Knowledge Networks also used

a dual sampling frame that included both

households that had telephones (including only

cell phones) and households that did not, as well

as households with listed and those with unlisted

telephone numbers. Knowledge Networks

recruited panel members randomly. Households

were provided with access to the Internet and

the necessary hardware if they needed it. For a

specific survey like ours, Knowledge Networks

selects panelists randomly, and no one not

selected may respond.

To calculate the survey’s response rate, we used

RR4, a method described by the American

Association for Public Opinion Research.

The RR4 method is based on multiplying the

recruitment rate (18.3 percent), the profile

rate (58.4 percent), and the completion rate

Before we pretested our survey, students in the Science,

Technology, and Public Policy Program at the Gerald R. Ford

School of Public Policy, University of Michigan, provided

input on issues related to governance and surveying public

opinion in the area of climate engineering.

(62.0 percent) to yield an overall response

rate of 7 percent. To reduce the potential for

nonresponse error, we weighted the survey data

using Knowledge Networks’ study-specific

post-stratification weight. From our assessment

of Knowledge Networks’ probability sampling

methods and weighting methodologies and

the results of our nonresponse bias analysis, we

determined that the sample selected for our study

was statistically representative of the U.S. adult

population.

Sampling error is a measure of the likely

variation introduced in a survey’s results by

using a probability procedure based on random

selections. In terms of the margin of error at the

95 percent confidence level, the sampling error

for survey estimates from the total sample is plus

or minus 4 percentage points, unless otherwise

noted. In terms of the margin of error at the

95 percent confidence level, the sampling error

for estimates based on subgroups of the sample

is plus or minus 9 percentage points, unless

otherwise noted. Because the overall response

rate was low and because sources of nonsampling

error such as differences in survey results from

panel attrition and panel conditioning might

be present, nonsampling error may also have

contributed to the total survey error of the results.

To avoid false precision, therefore, we rounded

the survey results we report in the text to the

nearest 5 percentage points.

The public perceptions elicited by this survey

are based on limited information about

geoengineering and do not necessarily predict

U.S. public views. We found that about

65 percent of the respondents had not heard

about geoengineering before reading the

survey; therefore, responses to the survey are

likely to reflect reactions to information about

geoengineering that we provided in the survey.

TECHNOLOGY ASSESSMENT GAO-11-71

If the respondents had been provided with

different information about geoengineering, the

survey responses could also differ. Also, climatic

or other events might change public views of

geoengineering. When we asked respondents

about their support for geoengineering research

or for government funding of geoengineering

research, we did not present them with

competing programs to choose from (programs

for cancer treatment, for example) or with

alternatives, such as using government funding

for national defense or cutting taxes. These kinds

of choices might have produced different results.

The initial version of the survey included

a question designed to help assess whether

the respondents thought that exploring

geoengineering solutions could distract from

other potential solutions to climate change,

such as reducing CO

emissions by driving less

or developing more fuel-efficient technologies.

Because the question included more than one

policy option on which respondents could hold

different views and focused on what respondents

would expect to happen in the future but could

not yield direct information about how members

of the public might actually behave, we revised

the survey to include a separate series of questions

to assess where initial support for geoengineering

might fall relative to other policy options.

8.1.4 External review

We invited all participants in the Meeting on

Climate Engineering to review our draft report.

We sent the draft report to the 16 participants

who agreed to review and help revise the report.

While we asked the 16 reviewers to focus on

the sections most relevant to their expertise, we

also told them that we welcomed any comments

on the entire draft. One of the 16 did not

participate in the review because of schedule

conflicts. Fifteen reviewers (see section 8.7)

provided technical or other comments that we

incorporated as appropriate. These 15 reviewers

were meeting participants who collectively

represented expertise relevant to each of the

three major areas of our report, including the

current state of climate engineering technology,

expert views of the future of climate engineering

research, and public perceptions of climate

engineering. The external review was conducted

in February 2011.

We conducted our work for this technology

assessment from January 2010 through July 2011

in accordance with GAO’s quality standards as

they pertain to technology assessments. Those

standards require that we plan and perform the

technology assessment to obtain sufficient and

appropriate evidence to provide a reasonable

basis for our findings and conclusions based on

our technology assessment objectives and that we

discuss limitations of our work. We believe that

the evidence we obtained provides a reasonable

basis for our findings and conclusions, based on

our technology assessment objectives.

8.2 Experts we consulted

on climate engineering

technologies

Barrett, Scott, Lenfest-Earth Institute Professor

of Natural Resource Economics, School of

International and Public Affairs and Earth

Institute, Columbia University, New York.

Benford, Gregory, Professor of Physics,

Department of Physics and Astronomy,

University of California, Irvine.

Caldeira, Ken, Physicist and Environmental

Scientist, Energy and Environmental Sciences

Directorate, Lawrence Livermore National

Laboratory, Livermore, California.

GAO-11-71 TECHNOLOGY ASSESSMENT

Crutzen, Paul J., Emeritus, Max Planck Institute

for Chemistry, Mainz, Germany; Institute

Scholar, International Institute for Applied

Systems Analysis, Laxenburg, Austria; Emeritus

Professor, Scripps Institution of Oceanography,

University of California at San Diego, La Jolla.

Doney, Scott C., Senior Scientist, Department

of Marine Chemistry and Geochemistry,

Woods Hole Oceanographic Institution,

Woods Hole, Massachusetts.

Ducklow, Hugh W., Director and Senior

Scientist, The Ecosystems Center, Marine

Biological Laboratory, Woods Hole,

Massachusetts; Professor, Department of Ecology

and Evolutionary Biology, Brown University,

Providence, Rhode Island.

Dyson, Freeman, Professor Emeritus, School of

Natural Sciences, Institute for Advanced Study,

Princeton, New Jersey.

Fahey, David W., Research Physicist,

Atmospheric and Chemical Processes, Chemical

Sciences Division, Earth System Research

Laboratory, National Oceanic and Atmospheric

Administration, Boulder, Colorado.

Garten, Jr., Charles T., Senior Research Staff

Member, Nutrient Biogeochemistry Group,

Environmental Sciences Division, Oak Ridge

National Laboratory, Oak Ridge, Tennessee.

Gibbons, John H. (Jack), President, Resource

Strategies, The Plains, Virginia; Consultant,

Lawrence Livermore National Research

Laboratory, Livermore, California; Division

Advisor, Division on Engineering and

Physical Sciences, The National Academies,

Washington, D.C.

Hack, James J., Director, National Center for

Computational Sciences, Oak Ridge National

Laboratory, Oak Ridge, Tennessee.

Keeling, Ralph, Professor, Scripps Institution of

Oceanography, University of California at San

Diego, La Jolla.

Keith, David, Director, ISEEE Energy and

Environmental Systems Group; Professor

and Canada Research Chair of Energy and

the Environment; Professor, Department of

Chemical and Petroleum Engineering, University

of Calgary, Calgary, Alberta, Canada; Adjunct

Professor, Department of Engineering and Public

Policy, Carnegie Mellon University, Pittsburgh,

Pennsylvania.

Lackner, Klaus, Department Chair, Ewing and

J. Lamar Worzel Professor of Geophysics, Earth

and Environmental Engineering and Director,

Lenfest Center for Sustainable Energy, The Earth

Institute, Columbia University, New York.

Latham, John, Emeritus Professor of Physics,

University of Manchester, United Kingdom;

Visiting Professor, University of Leeds, United

Kingdom; and Senior Research Associate,

National Center for Atmospheric Research,

Boulder, Colorado.

Lindzen, Richard S., Alfred P. Sloan Professor of

Meteorology, Department of Earth, Atmospheric,

and Planetary Sciences, Massachusetts Institute

of Technology, Cambridge, Massachusetts;

Distinguished Visiting Scientist, Jet Propulsion

Laboratory, California Institute of Technology,

Pasadena, California.

Long, Jane C. S., Associate Director, Energy and

Environment Directorate, Lawrence Livermore

National Laboratory, Livermore, California.

TECHNOLOGY ASSESSMENT GAO-11-71

MacCracken, Michael, Chief Scientist for

Climate Change Programs, Climate Institute,

Washington, D.C.

MacDonald, Alexander E. “Sandy,” Deputy

Assistant Administrator for Laboratories and

Cooperative Institutes, Office of Oceanic and

Atmospheric Research; Director, Earth System

Research Laboratory, National Oceanic and

Atmospheric Administration, Boulder, Colorado.

Marland, Gregg, Distinguished R&D Staff,

Environmental Sciences Division, Oak Ridge

National Laboratory, Oak Ridge, Tennessee;

Guest Professor, Ecotechnology Program, Mid

Sweden University, Östersund, Sweden.

Melillo, Jerry M., Distinguished Scientist,

The Ecosystems Center, Marine Biological

Laboratory, Woods Hole, Massachusetts;

Professor (MBL) of Ecology and

Evolutionary Biology, Department of

Ecology and Evolutionary Biology, Division

of Biology and Medicine, Brown University,

Providence, Rhode Island.

Morgan, M. Granger, University Professor,

Lord Chair Professor of Engineering, Head,

Department of Engineering and Public Policy,

Professor of Engineering and Public Policy and

of Electrical and Computer Engineering, and

Professor, The H. John Heinz III School of

Public Policy and Management, Carnegie Mellon

University, Pittsburgh, Pennsylvania.

Parson, Edward A. “Ted,” Joseph L. Sax

Collegiate Professor of Law and Professor

of Natural Resources and Environment,

University of Michigan, Ann Arbor, Michigan;

Senior Research Associate, Centre for Global

Studies, University of Victoria, British

Columbia, Canada.

Rasch, Philip, Chief Scientist for Climate

Science and Laboratory Fellow, Pacific Northwest

National Laboratory, Richland, Washington.

Ravishankara, A. R., Director, Chemical

Sciences Division, Earth System Research

Laboratory, National Oceanic and Atmospheric

Administration, Boulder, Colorado; Assistant

Professor, Department of Chemistry and

Biochemistry, and Affiliate, Cooperative

Institute for Research in Environmental Sciences,

University of Colorado, Boulder, Colorado.

Robock, Alan, Distinguished Professor (Professor

II), Department of Environmental Sciences;

Associate Director, Center for Environmental

Prediction; Director, Meteorology Undergraduate

Program; Member, Graduate Program in

Atmospheric Science, Rutgers University, New

Brunswick, New Jersey.

Rothstein, Lewis M., Professor of

Oceanography, Graduate School of

Oceanography and Treasurer, Metcalf Institute

Advisory Board, Metcalf Institute for Marine and

Environmental Reporting, University of Rhode

Island, Narragansett, Rhode Island.

Schneider, Stephen H., Melvin and Joan Lane

Professor for Interdisciplinary Environmental

Studies and Professor, Department of Biology,

Stanford University; Senior Fellow, Woods

Institute for the Environment; Professor, by

courtesy, Civil and Environmental Engineering,

Stanford University, Stanford, California

(deceased July 19, 2010).

Shepherd, John, Professorial Research Fellow

in Earth System Science, School of Ocean and

Earth Science, National Oceanography Centre,

University of Southampton, Southampton,

United Kingdom.

GAO-11-71 TECHNOLOGY ASSESSMENT

Socolow, Robert H., Professor, Department

of Aerospace and Mechanical Engineering;

Co-Director, Carbon Mitigation Initiative,

Princeton University, Princeton, New Jersey.

Somerville, Richard C. J., Distinguished

Professor Emeritus and Research Professor,

Scripps Institution of Oceanography, University

of California at San Diego, La Jolla; Team

Member, National Science Foundation Science

and Technology Center for Multiscaling

Modeling of Atmospheric Processes, Department

of Atmospheric Science, Colorado State

University, Fort Collins, Colorado.

Strand, Stuart E., Research Professor,

Department of Civil and Environmental

Engineering and School of Forest Resources,

University of Washington, Seattle, Washington.

Tilmes, Simone, Project Scientist I, Middle-

Upper Atmosphere and WACCM Group, The

Earth and Sun Systems Laboratory, National

Center for Atmospheric Research, Boulder,

Colorado.

Tombari, John, President, Schlumberger Carbon

Services, Houston, Texas.

8.3 Foresight scenarios

This appendix contains the four scenarios

depicting alternative futures that six external

experts worked with us to develop for use in

this technology assessment. Our purposes

in developing these scenarios included

(1) illustrating how some experts view alternative

possible futures (2010 to 2030) and judge

resulting risk levels (for 2030 and later years) and

(2) stimulating other experts’ thinking about the

future and eliciting their views.

Developing these scenarios constituted the

first of three steps we took to elicit a range

of views about the future. In the second and

third steps, we asked other experts to express

views or comment in response to the scenarios.

Specifically,

• in step 2, 28 experts responded to the scenarios;

and

• in step 3, 11 additional experts responded to

a description of the scenarios and a summary

that synthesized step-2 comments and views

about the future.

Although some commenters at both steps

critiqued or suggested improvements to the

scenarios (on points that concern, for example,

the effect of carbon constraints, the dollar values

associated with carbon constraints or research,

and the specification of risk), this appendix

presents the scenarios as they were when the

28 commenters first saw them.

Our report’s

methodology is detailed in section 8.1; the range

of views experts expressed across our three-step

process is represented in the body of the report.

It is important to keep in mind several

characteristics of the four scenarios. First, one

expert reviewing the scenarios drew our attention

to a two-part explanation of how carbon

constraints could affect CDR research (which

the scenarios do not describe): (1) establishing

The six external experts who participated in building the

scenarios are listed in section 8.4. Additionally, GAO’s Chief

Scientist, Timothy Persons, served as host and ex officio

member of the group.

The only exception consists of minor corrections to a

footnote.

TECHNOLOGY ASSESSMENT GAO-11-71

and maintaining a federal research program

that includes a significant CDR component

is more likely when people are confident that

CDR technologies will be used once successfully

developed and (2) establishing carbon constraints

could encourage the expectation that investing in

CDR research is worthwhile.

Next, whereas two of the scenarios (II and IV)

specify a degree of carbon constraint that is

equivalent to the effect of an international price

on CO

emissions applicable across all sectors

of all major emitting nations, the effect of such

a price is not comparable to the effect of prices

established for limited sectors or regions.

Further, Scenario II assumes “modest” research

funding starting at “tens of millions of dollars”

for a program involving several agencies. This

assumption was intended to apply to a dedicated

research effort for climate engineering that

excluded large-scale testing and deployment of

any of the technologies (which would be much

more expensive). It was not intended to include

relevant but separate research in a variety of

federal agencies. (Scenarios III and IV, which

describe greater research efforts, do not specify

funding levels. We discuss uncertainties about

funding in the body of the report.)

Finally, all four scenarios give examples of risk

for 2030 and later years. They present judgments

about levels of risk across three potential

developments—a future climate emergency

and response (that could involve decision

risks), continued future warming (that could

be associated with risks from climate change),

and no future warming (that might possibly

be associated in some scenarios with having

risked resources to prepare for a threat that did

not occur). Risk levels vary across the scenarios

and represent the combined effects of factors

that are varied across the scenarios, including

different levels of (1) climate engineering research

2010–30, and the technologies and information

developed from it, and (2) other factors in the

scenarios such as emissions reduction.

We present two key caveats concerning risk levels.

The scenarios present risk levels that represent

(1) inexact qualitative judgments that may

account for probability and potential severity and

(2) judgments about degree of risk that are not

necessarily comparable across the three potential

developments.

Nevertheless, comparisons can be

made across scenarios. For example, high decision

risk in one scenario and medium decision risk in

another implies a judgment that decision risk is

higher in one than in the other.

Finally, we note that the scenarios’ diagrams of

risk levels and CO

concentrations are not exact

but are, instead, illustrative approximations.

Scenario I:

Status quo

Between 2010 and 2015,

various efforts to jumpstart

global agreement on

carbon constraints have only token success.

Subsequent global efforts to stem carbon dioxide

(CO

) and other greenhouse gas emissions also

fail. Individual countries that favor reducing

emissions realize that they cannot “go it alone”

economically. Adaptation and mitigation

continue on paths set earlier.

MITRE (2011) illustrates how qualitative judgments of

probability and severity may be combined according to risk

management literature.

The twin goals of these efforts are to accelerate mitigation

efforts (that is, reduce carbon dioxide, or CO

, emissions) and

raise incentives for private-sector research, including research

on carbon dioxide removal (CDR) and sequestration.

III

GAO-11-71 TECHNOLOGY ASSESSMENT

Americans have diverse views about

climate change, and those who are aware of

geoengineering approaches remain skeptical about

their safety and utility. Debates on global carbon

constraints and U.S. geoengineering research

programs are limited to a small community of

academics, interest groups, and national decision-

makers. Proposed federal legislation to establish a

research program states four main goals:

(1) develop inexpensive, scalable carbon dioxide

removal (CDR) and sequestration methods

(using mechanical or biological approaches);

(2) understand and evaluate fast-acting methods

like stratospheric aerosol injection, including the

modeling of potential side effects and total cost

analyses; (3) involve other nations’ governments

and scientists in joint research and in setting

international research guidelines and limitations;

and (4) inform decision-makers about systemic

risks and tradeoffs among various geoengineering

technologies and between these and other climate

change approaches. But congressional efforts to

enact legislation fail, despite the support of nearly

half the Congress.

Without carbon constraints to stimulate private-

sector research and development (R&D) and

without a federal research program dedicated to

geoengineering, U.S. scientists focus their efforts

on other areas. The United States makes rapid

advances in emerging areas such as synthetic

biology and nanotechnology, but applications

to geoengineering are limited. Various other

nations (and some private sector organizations)

develop fast-acting technologies for use in a

climate emergency, but they do not always focus

on identifying side effects or share their results

with the global scientific community. Efforts to

develop international guidelines that limit field

tests and deployment fail.

Risks across three potential developments

(2030 and later years):

• Climate emergency and response: Immediate

decision risks would be very high if a sudden

acceleration of the warming trend occurred

spontaneously. World leaders would be under

pressure to make decisions quickly—and might

opt to use fast-acting, risky geoengineering

technologies—despite inadequate information

on their effectiveness and side effects.

(See red

bar in illustration.)

Waste

Warming

Emergency

Moderate

High

Low

Anticipated future risks

• Continued warming: Future global climate risks

would be high. As of 2030, this scenario sets

the United States and, indeed, the world, on

a path of increasing CO

emissions and rising

atmospheric concentrations. Decades of CDR

research starting in 2030 would be needed

prior to deployment aimed at decreasing

future CO

build-up. Prospects thus include

temperature increase and far future sea level

rise that might engulf vulnerable areas, naval

installations, and so forth; such a future

might also bring other very serious negative

consequences on a global scale. (See the line

chart and the orange bar in the bar chart.)

Similarly, without adequate information on fast-acting

technologies, it would be difficult for leaders to decide how to

respond to a surprise deployment by a single nation, terrorist

group, or some other “rogue” geoengineering effort.

TECHNOLOGY ASSESSMENT GAO-11-71

build-up

Past Future

• Resources wasted on geoengineering, if no future

warming: Risks of having wasted efforts and

expenditures would be near zero. This scenario

commits few, if any, new resources. (See gray

bar in the bar chart.)

Scenario II:

Some action

By 2015 or soon

thereafter, somewhat

improved data and models

of climate change reduce uncertainty and appear

to validate earlier conclusions about global

warming caused by human activity. A series of

extreme weather developments causes widespread

concern. As a result, major emitting nations

agree to new carbon constraints with strong

enforcement, but the reduction goals

and guidelines are limited (equivalent to a

$10 to $15 price on a ton of CO

). These

measures slightly increase both mitigation efforts

and existing incentives for private-sector R&D

on direct air capture and sequestration of CO

Scientists expect these changes will not stabilize

future accumulated levels of CO

but may delay a

far-off climate emergency by about 10 years and

represent a start.

Additionally, U.S. legislation

The moderate reductions are not at the scale required to

transform energy or energy-intensive industrial sectors.

establishes a modest geoengineering research

program that involves several federal agencies.

100

The funding level is tens of millions of dollars the

first year, with plans for modest annual increases.

Public acceptance of these developments is

mixed. The modest research program has no

public engagement or outreach component.

Without adequate information on the

general public’s views and concerns about

geoengineering, the government and scientists

do not craft the research program in a way that

encourages public acceptance, and inadvertently

they alienate some original supporters. Some

years of benign weather intervene. While

the research program continues to receive its

original level of support, the planned annual

expenditure increases are not put into effect.

The research program leverages its limited funds

by encouraging the private sector to develop

new methods of direct CO

air capture and

sequestration that are somewhat less expensive

than technologies developed through 2010.

But both in the United States and around the

globe, industries that emit significant CO

are

not eager to purchase the new technologies to

offset emissions: the limited carbon constraints

have not created a sufficient incentive. The

research program also makes some advances in

developing and evaluating fast-acting methods

like stratospheric aerosol injection, but research

by others outpaces the federal effort. Some new

fast-acting, high-impact technologies are not

rigorously evaluated for side effects. Results

are not always shared with the global scientific

community. Thus, we lack key information on

some new methods and their implications.

100

One option, among others, for housing a dedicated research

program, would be the U.S. Global Climate Change Research

Program.

III

GAO-11-71 TECHNOLOGY ASSESSMENT

Risks across three potential developments (2030

and later years):

• Climate emergency and response: Immediate

decision risks would be moderate to high.

By 2030, world leaders responding to an

emergency would have some geoengineering

information to guide them, but the

information would be inadequate for some new

technologies.

101

Waste

Warming

Emergency

Moderate

High

Low

Anticipated future risks

• Continued warming: Future global climate risks

would be moderate to high. As of 2030, more

is known about carbon emissions and controls

than in Scenario I. Still, starting serious R&D

on CDR in 2030 would mean years or decades

of delay before deployment. The world would

likely be on a path of continued build-up of

concentrations—although its trajectory

would be slightly slower/lower than in Scenario

I. The prospect of negative consequences like

sea level rise would still loom, eventually, in the

far future.

101

Also, relative to Scenario I, the increased knowledge might

better prepare decision-makers for responding to a “rogue”

deployment.

build-up

Past Future

• Resources wasted on geoengineering if no future

warming: Risks of having wasted efforts and

expenditures would be moderate. In the

absence of warming, some new geoengineering

technologies would not be useful, but others

might serve other purposes, such as helping to

reduce ocean acidification.

Scenario III:

Action on research

but not carbon

By 2015 or soon thereafter,

significantly improved data

and models of climate change appear to validate

earlier conclusions about anthropogenic global

warming. Highly disruptive and extreme weather

events affect the United States and many other

nations, causing waves of concern and even,

periodically, a crisis atmosphere. Other nations

pursue geoengineering research, a fact that is

widely reported. The balance of U.S. public

opinion turns toward taking action on climate

change, despite opposition from some at home

and the lack of global agreement on carbon

constraints.

Although public opinion generally favors

climate action, some opinion leaders believe

that, economically, the United States cannot

III

TECHNOLOGY ASSESSMENT GAO-11-71

“go it alone” in legislating carbon constraints.

Those who are opposed emphasize this point,

and legislative measures to step up U.S. emission

controls fail on a close vote. At the same time,

the Congress and the president work together

successfully to design and build support for

legislation that establishes an aggressive federal

geoengineering research program, starting with

moderate resources but progressing toward

a major funding commitment. The research

program involves public engagement to build

support in the years ahead (including years in

which extreme climate events may not occur);

establishes an adaptive strategy that entails

periodic reviews by an external body such as

the National Academies and horizon scans to

identify new opportunities; promotes innovation

through creative incentives, such as federal

contests with cash awards, in addition to using

more conventional approaches; and emphasizes

international cooperation. The main goals of this

research program are similar to those in the failed

legislation outlined in Scenario I (points 1–4).

As a result, major advances are made in

developing, understanding, and evaluating fast-

acting methods (like next-generation stratospheric

aerosol and injection methods); understanding

tradeoffs among different approaches; building

new approaches that reduce the potential for side

effects; and furthering basic science concerning

climate change. Other advances are made in

international cooperation on research limitations

and guidelines for the use of geoengineering.

Additionally, the research program helps

develop potentially transformative methods

of direct CO

air capture and sequestration.

These new technologies cost substantially less

than 2010 technologies but, given the lack

of carbon constraints, there are virtually no

incentives for emitting industries to buy them.

These technologies often fall into the “valley of

death” between R&D and commercial success

and large-scale deployment. Researchers and

commercial firms become discouraged. The focus

on direct air capture and sequestration suffers

some loss of credibility (that is, the government is

seen as investing in unused technologies), and it

is significantly cut back.

Risks across three potential developments (2030

and later years):

• Climate emergency and response: Immediate

decision risks would be moderate. By

2030, decision-makers have information to

support decisions about the use (or nonuse)

of fast-acting geoengineering technologies.

Catastrophic risks are minimized.

102

Waste

Warming

Emergency

Moderate

High

Low

Anticipated future risks

• Continued warming: Future global climate

risks would be high. Knowledge has increased

somewhat but—without utilization of CDR—

the world is still likely on a path of building up

the concentration of CO

in the atmosphere.

This brings the prospect of higher temperatures

102

Note, however, that in this scenario, decision-makers

who reject fast-acting technologies would lack alternative,

more gradual approaches for dealing with the problem. For

example, because CDR technologies were “left on the drawing

board” rather than being further developed and deployed,

decision-makers would not have the option of ramping up

existing direct air capture efforts. Decades would be likely to

be needed to prepare for such an effort.

GAO-11-71 TECHNOLOGY ASSESSMENT

which imply, in the far future, a sea level rise

and the possible consequences in Scenario I.

build-up

Past Future

• Resources wasted on geoengineering if no future

warming: Risks of having wasted efforts and

expenditures would be moderate. The financial

losses and efforts in a federal research program

designed specifically to combat warming could

be somewhat offset if some new technologies

can be used to address ocean acidification or

to develop spin-off technologies to apply in

other areas.

Scenario IV:

Major action

By 2015 or soon thereafter,

significantly stronger

climate-change data and

models will have reduced uncertainty, deepened

understanding, and validated earlier scientific

conclusions. Also during this half decade, several

unprecedented, highly disruptive, and extreme

weather events will affect a number of nations

(including the United States), causing mass

deaths, migration, and devastating property

damage. In a jarring development, one nation

unilaterally stages a major real-world test of a

fast-acting geoengineering technology in a remote

area—without first warning other nations. The

test’s negative effects are limited, but there is a

step jump increase in global recognition of the

need for coordination and cooperation.

In the United States, the balance of public

opinion tips toward favoring an aggressive

lowering of climate risks. Taking a leadership

role, U.S. envoys help achieve a global agreement

on relatively aggressive carbon constraints

(equivalent to a carbon price of $30 per ton of

). The global carbon constraints create a

worldwide incentive for the private sector to

pursue mitigation strategies, such as alternative

fuels and renewables, as well as geoengineering

approaches like scalable, direct air capture and

sequestration. A new presidential-congressional

initiative establishes an aggressive, innovative,

and adaptive geoengineering research program

that cuts across multiple agencies. It includes

strong international cooperation and other

goals similar to those in the failed legislation

outlined in Scenario I (points 1–4). Additionally,

this initiative emphasizes adaptation, research

innovation, and public engagement.

In part because of this research program,

new developments in areas such as synthetic

biology and nanotechnology are applied to

geoengineering (and to other areas such as

energy production and conservation), resulting

in a number of potentially game-changing

breakthroughs. The new U.S. initiative sets

in motion a range of programs and policies

to ensure that new technologies will have

opportunities to (1) transform energy sectors

and help lower future emissions in the United

States and around the globe, (2) reduce existing

and continuing build-up of CO

through

air capture (because emissions reduction will

not be complete), and (3) improve the U.S.

economic and export profile. Measures to spur

dissemination of new technologies include, for

III

TECHNOLOGY ASSESSMENT GAO-11-71

example, working with states and regions to

develop targeted sector or regional plans, as well

as international coordination.

Additionally, the research program includes

evaluations of side effects; analyses of economic,

legal, and social implications; and analyses of

tradeoffs and systemic risk—to help inform

policymakers and the interested public. Overall,

the program’s public engagement feature and its

effectuation of economic gains and international

cooperation help sustain support for this initiative

through 2030.

Risks across three potential developments

(2030 and later years):

• Climate emergency/response: Immediate decision

risks are low to moderate. By 2030, U.S.

decision-makers and the global community

would have information that helps prepare

them for responding to a climate emergency.

Additionally, there would be international

mechanisms in place to support global

cooperation, and thus help avoid conflicts.

Waste

Warming

Emergency

Moderate

High

Low

Anticipated future risks

• Continued warming: Future global climate risks

would be low to moderate. By 2030, the world

is on a path toward eventual stabilization and

subsequent reduction of CO

build-up—hence,

less warming. Although some sea level rise

may occur, the overall prospects for negative

consequences in the far future would be

substantially reduced relative to Scenarios I–III.

build-up

Past Future

• Resources wasted on geoengineering if no future

warming: Risks would be moderate to high. In

this scenario, very large investments (in terms

of both financial resources and efforts that

might have been used in other ways) would

have been made, and unrecoverable losses

could be significant. As in Scenarios II and

III, if discoveries and technologies developed

as a result of geoengineering research were

able to be used in other ways, losses could be

mitigated—for example, by helping to reduce

ocean acidification. In the longer term,

some of the geoengineering technologies

developed to combat warming might be used

instead to help avoid other adverse affects

that might be associated with extremely high

concentrations of CO

8.4 The six external experts

who participated in

building the scenarios

Cannizzaro, Christopher, Physical Science

Officer / AAAS Science and Technology

Policy Fellow, Office of Space and Advanced

Technology (OES/SAT), U.S. Department of

State, Washington, D.C.

GAO-11-71 TECHNOLOGY ASSESSMENT

100

Gallaudet, Tim, Deputy Director, Navy’s

Task Force Climate Change, Office of the

Oceanographer of the Navy, Chief of Naval

Operations Staff, Washington, D.C.

Lackner, Klaus, Department Chair, Ewing

and J. Lamar Worzel Professor of Geophysics,

Earth and Environmental Engineering; Director,

Lenfest Center for Sustainable Energy, The Earth

Institute, Columbia University, New York.

Patrinos, Aristides A. N., President, Synthetic

Genomics, La Jolla, California and

Washington, D.C.

Rasch, Philip, Chief Scientist for Climate

Science and Laboratory Fellow, Pacific Northwest

National Laboratory, Richland, Washington.

Rejeski,

David, Director, Science and

Technology Innovation Program, and Director,

Project on Emerging Nanotechnologies,

Woodrow Wilson International Center for

Scholars, Washington, D.C.

8.5 Experts who commented in

response to the scenarios

Barrett, Scott, Lenfest-Earth Institute Professor

of Natural Resource Economics, School of

International and Public Affairs and Earth

Institute, Columbia University, New York.

Beck, Robert A., Executive Vice President and

Chief Operating Officer, National Coal Council

Inc., Washington, D.C.

Bronson, Diana, Programme Manager and

Researcher, ETC Group, Ottawa,

Ontario, Canada.

Bunzl, Martin, Professor, Department of

Philosophy, Rutgers University; Director, Rutgers

Initiative on Climate and Social Policy, Rutgers

University, New Brunswick, New Jersey.

Carlson, Rob, Principal, Biodesic,

Seattle, Washington.

Cascio, Jamais, Senior Fellow, Institute for

Emerging Ethics and Technologies, Hartford,

Connecticut; Director of Impacts Analysis,

Center for Responsible Nanotechnology, Menlo

Park, California; Research Fellow, Institute for

the Future, Palo Alto, California.

Christy, John R., Distinguished Professor

of Atmospheric Science and Director,

Earth System Science Center, University of

Alabama, Huntsville, Alabama; Alabama State

Climatologist, The Alabama Office of the State

Climatologist, Huntsville, Alabama.

Fetter, Steve, Assistant Director At-Large,

U.S. Office of Science and Technology Policy,

Executive Office of the President of the United

States, Washington, D.C.

Fleming, James R., Professor and Director of

Science, Technology, and Society Program,

Colby College, Waterville, Maine.

Hamilton, Clive, Professor of Public Ethics,

Centre for Applied Philosophy and Public

Ethics, a joint center of the Australian National

University, Charles Sturt University, and

the University of Melbourne, Melbourne,

Australia; Vice-Chancellor’s Chair, Charles Sturt

University, Sydney, Australia.

Hawkins, David G., Director of Climate

Programs, Natural Resources Defense Council,

New York, New York.

Hsing, Helen, Managing Director, Strategic

Planning and External Liaison, U.S. Government

Accountability Office, Washington, D.C.

TECHNOLOGY ASSESSMENT GAO-11-71

101

Johnson, Jean, Executive Vice President,

Director of Education Insights and Director of

Programs, Public Agenda, New York, New York.

Khosla, Vinod, Partner, Khosla Ventures, Menlo

Park, California.

Lane, Lee, Visiting Fellow, Hudson Institute,

Washington, D.C.

Lomborg, Bjørn, Director, Copenhagen

Consensus Center, Denmark.

Long, Jane C. S., Associate Director, Energy and

Environment Directorate, Lawrence Livermore

National Laboratory, Livermore, California.

MacCracken, Michael, Chief Scientist for

Climate Change Programs, Climate Institute,

Washington, D.C.

Maynard, Andrew D., Director, University of

Michigan Risk Science Center, and Professor,

Environmental Health Sciences, School of

Public Health, University of Michigan,

Ann Arbor, Michigan.

Olson, Robert L., Senior Fellow, Institute for

Alternative Futures, Alexandria, Virginia.

Robock, Alan, Distinguished Professor

(Professor II), Department of Environmental

Sciences; Associate Director, Center for

Environmental Prediction; Director, Meteorology

Undergraduate Program; Member, Graduate

Program in Atmospheric Science, Rutgers

University, New Brunswick, New Jersey.

Sarewitz, Daniel, Co-Director, Consortium for

Science, Policy & Outcomes; Associate Director,

Center for Nanotechnology in Society; Professor

of Science and Society, College of Liberal Arts

and Sciences; and Professor, School of Life

Sciences and School of Sustainability, Arizona

State University, Tempe, Arizona.

Schneider, John P., Deputy Director for

Research, Earth System Research Laboratory,

National Oceanic and Atmospheric

Administration, Boulder, Colorado.

Seidel, Stephen, Vice President for Policy

Analysis and General Counsel, Pew Center on

Global Climate Change, Arlington, Virginia.

Suarez, Pablo, Associate Director of

Programmes, Red Cross/Red Crescent Climate

Centre, The Hague, The Netherlands; Visiting

Fellow, Frederick S. Pardee Center for the Study

of the Longer-Range Future, Boston University,

Boston, Massachusetts.

Victor, David G., Professor, International School

of International Relations and Pacific Studies;

Director, Laboratory on International Law and

Regulation, University of California at San

Diego, San Diego.

Wiener, Jonathan B., William R. and Thomas

L. Perkins Professor of Law and Director,

JD-LLM Program in International and

Comparative Law, Duke Law School, Durham,

North Carolina; Professor of Environmental

Policy, Nicholas School of the Environment and

Professor of Public Policy, Sanford School of

Public Policy, Duke University, Durham, N.C.;

Fellow, Resources for the Future, Wash., D.C.

Wilcoxen, Peter J., Director, Center for

Environmental Policy and Administration,

and Associate Professor, Economics and Public

Administration, The Maxwell School, Syracuse

University, Syracuse, New York; Nonresident

Senior Fellow, Economic Studies, The Brookings

Institution, Washington, D.C.

GAO-11-71 TECHNOLOGY ASSESSMENT

102

8.6 Experts who participated

in our meeting on

climate engineering

The 11 of these experts whose names are starred

(*) both (1) commented on the future of climate

engineering during the Meeting and (2) had not

previously participated in either constructing

the scenarios or commenting on them. We

discussed the views of these experts in section 4

of this report (Experts’ Views of the Future of

Climate Engineering Research). John Latham

was scheduled to attend this meeting but

was unable to be there and provided written

comments instead.

*Berg, Robert J., Trustee, World Academy of

Art and Science, Pittsburgh, Pennsylvania; Senior

Advisor, World Federation of United Nations

Associations, New York, New York.

Bunzl, Martin, Professor, Department of

Philosophy, Rutgers University; Director, Rutgers

Initiative on Climate and Social Policy, Rutgers

University, New Brunswick, New Jersey.

*Duren, Riley, Chief Systems Engineer,

Earth Science and Technology Directorate, Jet

Propulsion Laboratory, California Institute of

Technology, Pasadena, California.

Espinal, Laura, Materials Scientist, Ceramics

Division, Functional Properties Group, Material

Measurement Laboratory, National Institute

of Standards and Technology, Gaithersburg,

Maryland.

Fetter, Steve, Assistant Director At-Large,

U.S. Office of Science and Technology Policy,

Executive Office of the President of the United

States, Washington, D.C.

*Fraser, Gerald T., Chief, Optical Technology

Division, Physical Measurement Laboratory,

National Institute of Standards and Technology,

Gaithersburg, Maryland.

*Hunter, Kenneth W., Senior Fellow, Institute

for Global Chinese Affairs; Senior Fellow, Joint

Institute for Food Safety and Applied Nutrition,

University of Maryland, College Park, Maryland.

*Janetos, Anthony, Director, Joint Global

Change Research Institute, Pacific Northwest

National Laboratory and University of Maryland,

College Park, Maryland.

Johnson, Jean, Executive Vice President,

Director of Education Insights and Director of

Programs, Public Agenda, New York, New York.

*LaPorte, Todd R., Professor Emeritus of

Political Science, University of California,

Berkeley, California.

*Lehmann, Christopher Johannes, Associate

Professor, Department of Crop and Soil Sciences,

Cornell University, Ithaca, New York.

Long, Jane C. S., Associate Director, Energy and

Environment Directorate, Lawrence Livermore

National Laboratory, Livermore, California.

MacCracken, Michael, Chief Scientist for

Climate Change Programs, Climate Institute,

Washington, D.C.

*MacDonald, Alexander E. “Sandy,” Director,

Earth System Research Laboratory; and Deputy

Assistant Administrator for Laboratories and

Cooperative Institutes, Office of Oceanic and

Atmospheric Research, National Oceanic and

Atmospheric Administration, Boulder, Colorado.

TECHNOLOGY ASSESSMENT GAO-11-71

103

Rejeski, David, Director, Science and

Technology Innovation Program, and Director,

Project on Emerging Nanotechnologies,

Woodrow Wilson International Center for

Scholars, Washington, D.C.

*St. John, Courtney, Climate Change Affairs

Officer, Navy’s Task Force Climate Change,

Office of the Oceanographer of the Navy, Chief

of Naval Operations Staff, Washington, D.C.

Thernstrom, Samuel, Senior Policy Advisor,

Geoengineering Task Force, Bipartisan

Policy Center, Washington, D.C.; Senior

Climate Policy Advisor, Clean Air Task

Force, Boston, Massachusetts.

*Tilmes, Simone, Project Scientist I, Chemistry

Climate Liaison, Atmospheric Chemistry

Division, National Center for Atmospheric

Research, Boulder, Colorado.

Tombari, John, President, Schlumberger

Carbon Services, Houston, Texas.

*Toon, Owen B., Chair and Professor,

Department of Atmospheric and Oceanic

Sciences; Research Associate, Laboratory for

Atmospheric and Space Physics; Director,

Toon Aerosol Research Group, University of

Colorado, Boulder.

8.7 Reviewers of the

report draft

Duren, Riley, Chief Systems Engineer, Earth

Science and Technology Directorate, Jet

Propulsion Laboratory, California Institute of

Technology, Pasadena, California.

Espinal, Laura, Materials Scientist, Ceramics

Division, Functional Properties Group,

Material Measurement Laboratory, National

Institute of Standards and Technology,

Gaithersburg, Maryland.

Fraser, Gerald T., Chief, Optical Technology

Division, Physical Measurement Laboratory,

National Institute of Standards and Technology,

Gaithersburg, Maryland.

Hunter, Kenneth W., Senior Fellow, Institute

for Global Chinese Affairs; Senior Fellow, Joint

Institute for Food Safety and Applied Nutrition,

University of Maryland, College Park, Maryland.

Janetos, Anthony, Director, Joint Global

Change Research Institute, Pacific Northwest

National Laboratory, and University of

Maryland, College Park, Maryland.

Johnson, Jean, Executive Vice President,

Director of Education Insights and Director of

Programs, Public Agenda, New York, New York.

LaPorte, Todd R., Professor Emeritus of

Political Science, University of California,

Berkeley.

Latham, John, Emeritus Professor of Physics,

University of Manchester, UK; Visiting Professor,

University of Leeds, UK; Senior Research

Associate, National Center for Atmospheric

Research, Boulder, Colorado.

Lehmann, Christopher Johannes, Associate

Professor, Department of Crop and Soil Sciences,

Cornell University, Ithaca, New York.

MacCracken, Michael, Chief Scientist for

Climate Change Programs, Climate Institute,

Washington, D.C.

MacDonald, Alexander E. “Sandy,” Director,

Earth System Research Laboratory, and Deputy

GAO-11-71 TECHNOLOGY ASSESSMENT

104

Assistant Administrator for Laboratories and

Cooperative Institutes, Office of Oceanic and

Atmospheric Research, National Oceanic and

Atmospheric Administration, Boulder, Colorado.

St. John, Courtney, Climate Change Affairs

Officer, Navy’s Task Force Climate Change,

Office of the Oceanographer of the Navy, Chief

of Naval Operations Staff, Washington, D.C.

Thernstrom, Samuel, Senior Policy Advisor,

Geoengineering Task Force, Bipartisan

Policy Center, Washington, D.C.; Senior

Climate Policy Advisor, Clean Air Task Force,

Boston, Massachusetts.

Tilmes, Simone, Project Scientist I, Chemistry

Climate Liaison, Atmospheric Chemistry

Division, National Center for Atmospheric

Research, Boulder, Colorado.

Toon, Owen B., Chair and Professor,

Department of Atmospheric and Oceanic

Sciences; Research Associate, Laboratory for

Atmospheric and Space Physics; Director,

Toon Aerosol Research Group, University of

Colorado, Boulder.

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