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Summary
C
limate change is occurring, is very likely caused by human activities, and poses
significant risks for a broad range of human and natural systems. Each additional
ton of greenhouse gases emitted commits us to further change and greater
risks. In the judgment of the Committee on America’s Climate Choices, the environ-
mental, economic, and humanitarian risks of climate change indicate a pressing need
for substantial action to limit the magnitude of climate change and to prepare to
adapt to its impacts.
This report, the final volume of the America’s Climate Choices (ACC) suite of activities,
examines the nation’s options for responding to the risks posed by climate change.
Although it is crucial to recognize that climate change is inherently an international
concern that requires response efforts from all countries, this report focuses on the
essential elements of an effective national response, which includes:
• Enacting policies and programs that reduce risk by limiting the causes of cli-
mate change and reducing vulnerability to its impacts;
• Investing in research and development efforts that increase knowledge and
improve the number and effectiveness of response options available;
• Developing institutions and processes that ensure pertinent information is
collected and that link scientific and technical analysis with public deliberation
and decision making;
• Periodically evaluating how response efforts are progressing and updating
response goals and strategies in light of new information and understanding.
Given the inherent complexities of the climate system, and the many social, economic,
technological, and other factors that affect the climate system, we can expect always
to be learning more and to be facing uncertainties regarding future risks. This is not,
however, a reason for inaction. Rather, the challenge for society is to acknowledge
these uncertainties and respond accordingly, just as is done in many areas of life. For
example, people buy home insurance to protect against potential losses, and busi-
nesses plan contingently for a range of possible future economic conditions.
Just as in these other areas, a valuable framework for making decisions about Ameri-
ca’s Climate Choices is iterative risk management. This refers to an ongoing process
of identifying risks and response options, advancing a portfolio of actions that em-
phasize risk reduction and are robust across a range of possible futures, and revising
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A M E R I C A’ S C L I M AT E C H O I C E S
responses over time to take advantage of new knowledge. Iterative risk management
strategies must be durable enough to promote sustained progress and long-term
investments, yet sufficiently flexible to take advantage of improvements in knowledge,
tools, and technologies over time.
In the context of an iterative risk management framework, and building on the analy-
ses in the four ACC panel reports, the committee recommends the following priority
actions for an effective and comprehensive national response to climate change:
Substantially reduce greenhouse gas emissions. In the committee’s judgment there
are many reasons why it is imprudent to delay actions that at least begin the process
of substantially reducing emissions. For instance:
• The faster emissions are reduced, the lower the risks posed by climate change.
Delays in reducing emissions could commit the planet to a wide range of ad-
verse impacts, especially if the sensitivity of the climate to greenhouse gases is
on the higher end of the estimated range.
• Waiting for unacceptable impacts to occur before taking action is imprudent
because the effects of greenhouse gas emissions do not fully manifest them-
selves for decades and, once manifested, many of these changes will persist for
hundreds or even thousands of years.
• The sooner that serious efforts to reduce greenhouse gas emissions proceed,
the less pressure there will be to make steeper (and thus likely more expen-
sive) emission reductions later.
• The United States and the rest of the world are currently making major invest-
ments in new energy infrastructure that will largely determine the trajectory
of emissions for decades to come. Getting the relevant incentives and policies
in place as soon as possible will provide crucial guidance for these investment
decisions.
• In the committee’s judgment, the risks associated with doing business as usual
are a much greater concern than the risks associated with engaging in strong
response efforts. This is because many aspects of an “overly ambitious” policy
response could be reversed if needed, through subsequent policy change;
whereas adverse changes in the climate system are much more difficult (in-
deed, on the timescale of our lifetimes, may be impossible) to “undo.”
RECOMMENDATION 1: In order to minimize the risks of climate change and its ad-
verse impacts, the nation should reduce greenhouse gas emissions substantially over
the coming decades. The exact magnitude and speed of emissions reduction depends
on societal judgments about how much risk is acceptable. However, given the inertia
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Summary
of the energy system and long lifetime associated with most infrastructure for energy
production and use, it is the committee’s judgment that the most effective strategy is
to begin ramping down emissions as soon as possible.
Emission reductions can be achieved in part through expanding current local, state,
and regional-level efforts, but analyses suggest that the best way to amplify and ac-
celerate such efforts, and to minimize overall costs (for any given national emissions
reduction target), is with a comprehensive, nationally uniform, increasing price on
CO21 emissions, with a price trajectory sufficient to drive major investments in energy
efficiency and low-carbon technologies. In addition, strategically-targeted comple-
mentary policies are needed to ensure progress in key areas of opportunity where
market failures and institutional barriers can limit the effectiveness of a carbon pricing
system.
Begin mobilizing now for adaptation. Aggressive emissions reductions would reduce
the need for adaptation, but not eliminate it. Climate change is already happening,
and additional changes can be expected for all plausible scenarios of future green-
house gas emissions. Prudent risk management demands advanced planning to deal
with possible adverse outcomes—known and unknown—by increasing the nation’s
resilience to both gradual changes and the possibility of abrupt disaster events. Effec-
tive adaptation will require the development of new tools and institutions to manage
climate-related risks across a broad range of sectors and spatial scales. Adaptation
decisions will be made and implemented by actors in state and local governments, the
private sector, and society at large, but there is also a need for national-level efforts—
for instance, to share information and technical resources for evaluating vulnerability
and adaptation options, and to develop and implement adaptation plans within the
federal agencies and their relevant programs.
RECOMMENDATION 2: Adaptation planning and implementation should be initiated
at all levels of society. The federal government, in collaboration with other levels of
government and with other stakeholders, should immediately undertake the develop-
ment of a national adaptation strategy and build durable institutions to implement
that strategy and improve it over time.
Invest in science, technology, and information systems. Scientific research and
technology development can expand the range, and improve the effectiveness of,
options to respond to climate change. Systems for collecting and sharing information,
including formal and informal education systems, can help ensure that climate-related
decisions are informed by the best available knowledge and analysis, and can help us
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A M E R I C A’ S C L I M AT E C H O I C E S
evaluate the effectiveness of actions taken. Many actors are involved in such efforts.
For instance, technological innovation will depend in large part on private sector
efforts, while information, education, and stakeholder engagement systems can be
advanced by nongovernmental organizations and state and local governments. But
the federal government has important roles to play in all of these efforts as well.
RECOMMENDATION 3: The federal government should maintain an integrated,
coordinated, and expanded portfolio of research programs with the dual aims of
increasing our understanding of the causes and consequences of climate change and
enhancing our ability to limit climate change and to adapt to its impacts.
RECOMMENDATION 4: The federal government should lead in developing, support-
ing, and coordinating the information systems needed to inform and evaluate Amer-
ica’s climate choices, to ensure legitimacy and access to climate services, greenhouse
gas accounting systems, and educational information.
RECOMMENDATION 5: The nation’s climate change response efforts should include
broad-based deliberative processes for assuring public and private-sector engage-
ment with scientific analyses, and with the development, implementation, and peri-
odic review of public policies.
Actively engage in international climate change response efforts. America’s climate
choices affect and are affected by the choices made throughout the world. U.S. emis-
sions reductions alone will not be adequate to avert dangerous climate change risks,
but strong U.S. emission reduction efforts will enhance our ability to influence other
countries to do the same. Also, the United States can be greatly affected by impacts
of climate change occurring elsewhere in the world, and it is in our interest to help
enhance the adaptive capacity of other nations. Effectively addressing climate change
requires both contributing to and learning from other countries’ efforts.
RECOMMENDATION 6: The United States should actively engage in international-
level climate change response efforts: to reduce greenhouse gas emissions through
cooperative technology development and sharing of expertise, to enhance adaptive
capabilities (particularly among developing nations that lack the needed resources),
and to advance the research and observations necessary to better understand the
causes and effects of climate change.
Coordinate national response efforts. Individuals, businesses, state and local govern-
ments, and other decision makers nationwide are already taking steps to respond to
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climate change risks, and must continue to play essential roles in our nation’s future
response strategies. Numerous federal government agencies and organizations must
also be involved in informing and implementing America’s climate choices. Our na-
tion needs a coherent strategy for assuring adequate coordination among this wide
array of actors. This includes, for instance, carefully balancing rights and responsibili-
ties among different levels of government (vertical coordination), assuring effective
delineation of roles among different federal agencies (horizontal coordination), and
promoting effective integration among the different components of a comprehensive
climate change response strategy (e.g., all the various efforts discussed in each of the
previous recommendations).
RECOMMENDATION 7: The federal government should facilitate coordination of the
many interrelated components of America’s response to climate change with a pro-
cess that identifies the most critical coordination issues and recommends concrete
steps for how to address these issues.
Responding to the risks of climate change is one of the most important challenges
facing the United States and the world today and for decades to come. America’s
climate choices will involve political and value judgments by decision makers at all
levels. These choices, however, must be informed by sound scientific analyses. This
report recommends a diversified portfolio of actions, combined with a concerted ef-
fort to learn from experience as those actions proceed, to lay the foundation for sound
decision making today and expand the set of options available to decision makers in
the future.
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