Download Climate Intervention Is Not a Replacement for Reducing Carbon

Climate Intervention Is Not a Replacement for Reducing Carbon Emissions;
Proposed Intervention Techniques Not Ready for Wide-Scale Deployment
Date: Feb. 10, 2015
WASHINGTON – There is no substitute for dramatic reductions in greenhouse gas emissions to
mitigate the negative consequences of climate change, a National Research Council committee
concluded in a two-volume evaluation of proposed climate-intervention techniques. Strategies to
remove carbon dioxide from the atmosphere are limited by cost and technological immaturity, but
they could contribute to a broader portfolio of climate change responses with further research and
development. Albedo-modification technologies, which aim to increase the ability of Earth or
clouds to reflect incoming sunlight, pose considerable risks and should not be deployed at this
time.
Carbon dioxide removal and albedo-modification techniques have been grouped up until now
under the common term “geoengineering,” but they vary widely with respect to environmental
risks, socio-economic impacts, cost, and research needs. Carbon dioxide removal addresses the
root cause of climate change -- high concentrations of the greenhouse gas in the atmosphere -and generally have well-understood benefits and risks, but current technologies would take
decades to achieve moderate results and be cost-prohibitive at scales large enough to have a
sizeable impact. By contrast, albedo-modification techniques would only temporarily mask the
warming effect caused by high CO2 concentrations, and present serious known and possible
unknown environmental, social, and political risks, including the possibility of being deployed
unilaterally.
These differences led the committee to evaluate the two types of approaches separately in
companion reports, a distinction it hopes carries over to future scientific and policy discussions.
In addition, the committee believes that these approaches are more accurately described as
“climate intervention” strategies -- purposeful actions intended to curb the negative impacts of
climate change -- rather than engineering strategies that imply precise control over the climate.
“That scientists are even considering technological interventions should be a wake-up call that we
need to do more now to reduce emissions, which is the most effective, least risky way to combat
climate change,” said committee chair Marcia McNutt, editor-in-chief of Science and former
director of the U.S. Geological Survey. “But the longer we wait, the more likely it will become that
we will need to deploy some forms of carbon dioxide removal to avoid the worst impacts of
climate change.”
If society ultimately decides to intervene in Earth’s climate, any actions should be informed by a
far more substantive body of scientific research, including ethical and social dimensions, than is
presently available, the committee said. Decisions regarding deployment of carbon dioxide
removal technologies will be largely based on cost and scalability, and research is needed to
make current options more effective, more environmentally friendly, and less costly. Conversely,
any future decision about albedo modification will be judged primarily on questions of risk, and
there are many opportunities to conduct research that furthers basic understanding of the climate
system and its human dimensions -- without imposing the risks of large-scale deployment -- that
would better inform societal considerations.
“If the world cannot slow emissions or the effects of climate change are more extreme or occur
sooner than expected, there may be demands to pursue additional climate-intervention
technologies about which scientists need a better understanding,” said National Academy of
Sciences President Ralph J. Cicerone. “Although riskier ideas to lessen the amount of energy
absorbed from the sun should not be considered for deployment, they should be studied so that
we can provide answers if someday these ideas begin to be considered in attempts to avert
catastrophe. These reports should guide federal agencies in supporting research on climate-
intervention technologies, while keeping separate any decision-making about their
implementation.”
Carbon dioxide removal and sequestration
Some carbon dioxide removal strategies seek to enhance or mimic the natural processes that
already remove about half of the world’s carbon emissions from the atmosphere each year.
Environmental risks vary among the proposed technologies (listed below), but overall the risks
are relatively low and generally understood. However, most carbon dioxide removal strategies
have limited technical capacity, and absent some unforeseen technological innovation, largescale deployment would cost as much or more than replacing fossil fuels with low carbonemission energy sources, the committee said.
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Land-management approaches such as forest restoration and low-till agriculture are
mature, readily deployable technologies with well-known environmental consequences.
Enhanced weathering processes on land and in the ocean to accelerate natural removal
of carbon dioxide from the atmosphere have only been carried out on a limited scale with
intermediate technological readiness. Ocean-based approaches in particular carry
significant environmental and socio-political risks.
Ocean iron fertilization is an immature technology whose high costs and technical and
environmental risks currently outweigh the benefits.
Approaches in which biomass is converted to heat, electricity, or liquid or gas fuels
followed by CO2 capture and sequestration are limited by the availability of land for
biomass cultivation and the need to transport it to processing facilities.
Direct air capture of carbon is an immature technology with only laboratory experiments
carried out to date and demonstration projects in progress. Technologies for storing the
captured carbon are at an intermediate stage, but only prototypes exist and are not at the
scale required for significant sequestration.
The committee recommended federal research and development investment to improve methods
of carbon dioxide removal and disposal at scales that would have a significant global climate
impact. In particular, research is needed to minimize energy and materials consumption, identify
and quantify risks, lower costs, and develop reliable sequestration and monitoring capabilities.
Albedo-modification research
Technologies that prevent sunlight from reaching Earth’s surface could reduce average global
temperatures within a few years, similar to the effects of large volcanic eruptions. While many
albedo-modification techniques have been proposed, the committee said two strategies that could
potentially have a significant impact are injection of aerosols into the stratosphere and marine
cloud brightening. Unlike carbon dioxide removal, these methods would not require major
technological innovation to be implemented and are relatively inexpensive compared with the
costs of transitioning to a carbon-free economy.
However, albedo modification would only temporarily mask the warming effect of greenhouse
gases and would not address atmospheric concentrations of CO2 or related impacts such as
ocean acidification. In the absence of CO2 reductions, albedo-modification activities would need
to be sustained indefinitely and at increasingly large scales to offset warming, with severe
negative consequences if they were to be terminated. In addition, albedo modification introduces
secondary effects on the ozone layer, precipitation patterns, terrestrial and marine ecosystems,
and human health, with unknown social, political, and economic outcomes.
Many of the processes most relevant to albedo modification -- such as those that control the
formation of clouds and aerosols -- are among the most difficult components of the climate
system to model and monitor. Present-day observational capabilities lack sufficient capacity to
monitor the environmental effects of an albedo-modification deployment. Improvements in the
capacity to monitor direct and indirect changes on weather, climate, or larger Earth systems and
to detect unilateral or uncoordinated deployment could help further understanding of albedo
modification and climate science generally.
The committee said it would be “irrational and irresponsible” to implement sustained albedo
modification without also pursuing emissions mitigation, carbon dioxide removal, or both. It
opposed deployment of albedo-modification techniques, but recommended further research,
particularly “multiple-benefit” research that simultaneously advances basic understanding of the
climate system and quantifies the technologies’ potential costs, intended and unintended
consequences, and risks.
Albedo-modification research will have legal, ethical, social, political, and economic ramifications.
The committee recommended the initiation of a serious deliberative process to examine what
international research governance structures may be needed beyond those that already exist,
and what types of research would require such governance. The degree and nature of
governance should vary by activity and the associated risks, and should involve civil society in
decision-making through a transparent and open process.
The study was sponsored by the National Academy of Sciences, U.S. intelligence community,
National Aeronautics and Space Administration, National Oceanic and Atmospheric
Administration, and U.S. Department of Energy. The National Academy of Sciences, National
Academy of Engineering, Institute of Medicine, and National Research Council are private,
independent nonprofit institutions that provide science, technology, and health policy advice
under a congressional charter granted to NAS in 1863. The National Research Council is the
principal operating arm of the National Academy of Sciences and the National Academy of
Engineering. For more information, visit http://national-academies.org. A committee roster
follows.
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Pre-publication copies of Climate Intervention: Carbon Dioxide Removal and Reliable
Sequestration and Climate Intervention: Reflecting Sunlight to Cool Earth are available from
the National Academies Press on the Internet at http://www.nap.edu or by calling 202-334-3313
or 1-800-624-6242. Reporters may obtain a copy from the Office of News and Public Information
(contacts listed above).
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NATIONAL RESEARCH COUNCIL
Division on Earth and Life Studies
Board on Atmospheric Sciences and Climate
Committee on Geoengineering Climate: Technical Evaluation and Discussion of Impacts
Marcia K. McNutt* (chair)
Editor-in-Chief
Science
American Association for the Advancement of Science
Washington, D.C.
Waleed Abdalati
Professor, Department of Geography, and
Director, Cooperative Institute for Research in Environmental Sciences
University of Colorado Boulder
Boulder
Ken Caldeira
Senior Member
Department of Global Ecology
Carnegie Institution for Science; and
Professor
Environmental Earth System Sciences Department
Stanford University
Stanford, Calif.
Scott C. Doney
Senior Scientist and Chair
Department of Marine Chemistry and Geochemistry
Woods Hole Oceanographic Institution
Woods Hole, Mass.
Paul G. Falkowski*
Bennett L. Smith Professor of Business and Natural Resources
Department of Earth and Planetary Sciences, and
Lead Principal
Environmental Biophysics and Molecular Ecology Program
Rutgers University
New Brunswick, N.J.
Steven Fetter
Associate Provost for Academic Affairs, and
Professor
Maryland School of Public Policy
University of Maryland
College Park
James R. Fleming
Professor of Science, Technology, and Society
Colby College
Waterville, Maine
Steven P. Hamburg
Chief Scientist
Environmental Defense Fund
Boston
M. Granger Morgan*
Lord Chair Professor in Engineering,
Professor and Department Head
Engineering and Public Policy,
Professor in Electrical and Computer Engineering, and
Professor
The H. John Heinz III School of Public Policy
Carnegie Mellon University
Pittsburgh
Joyce E. Penner
Ralph J. Cicerone Distinguished University Professor of Atmospheric Science, and
Associate Chair
Department of Atmospheric, Oceanic, and Space Sciences
University of Michigan
Ann Arbor
Raymond T. Pierrehumbert
Louis Block Professor
Department of Geophysical Sciences
Hinds Geological Laboratory
University of Chicago
Chicago
Philip J. Rasch
Chief Scientist for Climate Science
Pacific Northwest National Laboratory
Richland, Wash.
Lynn M. Russell
Professor
Climate, Ocean, and Atmosphere Program
Scripps Institution of Oceanography
La Jolla, Calif.
John T. Snow
Regents’ Professor of Meteorology, and
Dean Emeritus
College of Atmospheric and Geographic Sciences
University of Oklahoma
Norman
David W. Titley
Director
Center for Solutions to Weather and Climate Risk
Department of Meteorology
Pennsylvania State University
University Park
Jennifer Wilcox
Assistant Professor of Energy Resources Engineering
Department of Energy
School of Earth Sciences, and
Affiliate Faculty Member
Emmet Interdisciplinary Program for the Environment and Resources
Stanford University
Stanford, Calif.
STAFF
Edward Dunlea
Study Director
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*Member, National Academy of Sciences