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OCR for page 30
Making
Part III Climate CHOICES
A strong body of
evidence shows that
climate change is occurring,
As a result, decision makers of all types--including
individuals, businesses, and governments at all levels--
are taking or planning actions to respond to climate
is caused largely by human change. Depending on how much emissions are
activities, and poses signifi- curtailed, the future could bring a relatively mild
cant risks for a broad range change in climate or it could deliver extreme
of human and natural changes that could last thousands of years. The
systems. nation's scientific enterprise can contribute both by
continuing to improve understanding of the causes
and consequences of climate change and by improving
and expanding the options available to limit the magnitude of
climate change and to adapt to its impacts.
30
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How does science inform
emissions choices?
A s discussed in Part II of this booklet, improve-
ments in the ability to predict climate change
impacts per degree of warming has made it easier
Even with expected improvements in energy ef-
ficiency, if the world continues with "business as
usual" in the way it uses and produce energy, CO2
to evaluate the risks of climate change. Policymak- emissions will continue to accumulate in the atmo-
ers are left to address two fundamental questions: sphere and warm Earth.2 As illustrated in Figure 29,
(1) at what level of warming are risks acceptable to keep atmospheric concentrations of CO2 roughly
given the cost of limiting them; and (2) what level steady for a few decades at any given level to avoid
of emissions will keep Earth within that level of increasing climate change impacts, global emissions
warming? Science cannot answer the first question, would have to be reduced by 80%.
because it involves many value judgments outside Another helpful concept is that the amount of
the realm of science. However, much progress has warming expected to occur from CO2 emissions
been made in answering the second. depends on the cumulative amount of carbon emis-
sions, not on how quickly or slowly the carbon is
added to the atmosphere (Figure 30). Humans have
emitted about 500 billion tons (gigatonnes) of car-
bon to date. Best estimates indicate that adding
about 1,150 billion tons of carbon to the air would
lead to a global mean warming of 2°C (3.6°F).
2Other greenhouse gases are a factor, but CO is by far
2
the most important greenhouse gas in terms of long-term
climate change effects.
MA K ING C LIMATE C H O IC E S
FIGURE 29
Illustrative Example: How Emissions Relate to CO2
Concentrations. Sharp reductions in emissions are
needed to stop the rise in atmospheric concentrations
of CO2 and meet any chosen stabilization target. The FIGURE 30
graphs show how changes in carbon emissions (top
panel) are related to changes in atmospheric concen- Cumulative Emissions and Increases in Global Mean
trations (bottom panel). It would take an 80% reduc- Temperature Recent studies show that for a particular
tion in emissions (green line, top panel) to stabilize choice of climate stabilization temperature, there would
atmospheric concentrations (green line, bottom panel) be only a certain range of allowable cumulative carbon
for any chosen stabilization target. Stabilizing emis- emissions. Humans have emitted a total of about 500 bil-
sions (blue line, top panel) would result in a continued lion tons (gigatonnes) of carbon emissions to date. The
rise in atmospheric concentrations (blue line, bottom error bars account for estimated uncertainties in both
panel), but not as steep as a rise if emissions continue the carbon cycle (how fast CO2 will be taken up by the
to increase (red lines). Source: National Research Council, oceans) and in the climate responses to CO2 emissions.
2011a Source: National Research Council, 2011a
31
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Adding CO2 more quickly would bring tempera-
tures to that value more quickly, but the value itself
would change very little.
Because cumulative emissions are what matters,
policies oriented toward the very long term (several
decades into the future) might be able to focus less
on specifying exactly when reductions must take
place and more on how much total emissions are al-
lowed over a long period--in effect, a carbon budget.
Such a budget would specify the amount of total FIGURE 31
greenhouse gas that can be emitted during a speci- Meeting an Emissions Budget Meeting any emissions
fied period of time (say, between now and 2050). budget will be easier the sooner and more aggressively
actions are taken to reduce emissions. Source: National
Meeting any specific emissions budget is more Research Council
likely the earlier and more aggressively work is done
to reduce emissions (Figure 31). It's like going on a reach that goal if he or she begins eating less and
diet. If a person wants to lose 40 pounds by a cer- exercising more as soon as possible, rather than
tain event in the future, it would be much easier to waiting to start until the month before the event.
What are the choices for reducing
greenhouse gas emissions?
A s discussed earlier, to limit climate India will continue to grow. Thus,
change in the long term, the most reductions in U.S. emissions
important greenhouse gas to control alone will not be adequate to
is carbon dioxide, which in the avert climate change risks.
United States is emitted primarily However, strong U.S. lead-
as a result of burning fossil fuels. ership--demonstrated
Figure 32 shows the relative through strong domestic
amount of emissions from resi- actions, may help influ-
dential, commercial, industrial, ence other countries to
and transportation sources. It's pursue serious emission
not really a matter of doing with- reduction efforts as well.
out, but being smarter about how we Several key opportunities to
produce and use energy. reduce how much carbon dioxide
The United States is responsible for about accumulates in the atmosphere are
half of the human-produced CO2 emissions already available (Figure 33), including:
in the atmosphere and currently accounts for Reduce underlying demand for goods and ser-
roughly 20% of global CO2 emissions, despite hav- vices that require energy, for example, expand
ing only 5% of the world's population. The U.S. education and incentive programs to influence
percentage of total global emissions is projected to consumer behavior and preferences; curtail sprawl-
decline over the coming decades as emissions ing development patterns that further our depen-
from rapidly developing nations such as China and dence on petroleum.
32
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investments and on the behavioral and consumer
choices of individual households. Governments at
federal, state, and local levels have a large role to
play in influencing these key stakeholders through
effective policies and incentives. In general, there are
four major tool chests from which to select policies
for driving emission reductions:
· Pricing of emissions such as by means of a car-
FIGURE 32 bon tax or cap-and-trade system;
U.S. greenhouse gas emissions in 2009 show the rela-
· mandates or regulations that could include
tive contribution from four end-uses: residential, com-
mercial (e.g., retail stores, office buildings), industrial, direct controls on emitters (for example,
and transportation. Electricity consumption accounts through the Clean Air Act) or mandates such as
for the majority of energy use in the residential and
automobile fuel economy standards, appliance
commercial sectors. Image courtesy: U.S. Environmental
Protection Agency efficiency standards, labeling requirements,
building codes, and renewable or low-carbon
Improve the efficiency with which energy is portfolio standards for electricity generation;
used, for example, use more efficient methods for · public subsidies for emission-reducing choices
insulating, heating, cooling, and lighting buildings; through the tax code, appropriations, or loan
upgrade industrial equipment and processes to be guarantees; and
more energy efficient; and encourage the purchase
· providing information and education and pro-
of efficient home appliances and vehicles.
moting voluntary measures to reduce emissions.
Expand the use of low- and zero-carbon energy
A comprehensive national program would likely
sources, for example, switch from coal and oil to
use tools from all of these areas. Most economists
natural gas, expand the use of nuclear power and
and policy analysts have concluded, however, that
renewable energy sources such as solar, wind, geo-
putting a price on CO2 emissions that is sufficiently
thermal, hydropower, and biomass; capture and
high and rises over time is the least costly path to
sequester CO2 from power plants and factories.
significantly reduce emissions; and it is the most ef-
Capture and sequester CO2 directly from the ficient incentive for innovation and the long-term
atmosphere, for example, manage forests and soils investments necessary to develop and deploy energy
to enhance carbon uptake; develop mechanical efficient and low-carbon technologies and infrastruc-
methods to "scrub" CO2 directly from ambient air. ture. Complementary policies may also be needed,
MA K ING C LIMATE C H O IC E S
Advancing these opportunities to reduce emis- however, to ensure rapid progress in key areas.
sions will depend to a large degree on private sector
Key Opportunities for Reducing
Emissions A chain of factors deter-
mine how much CO2 accumulates in
the atmosphere. Better outcomes
(gold ellipses) could result if the
nation focuses on several opportunities
within each of the blue boxes. Source:
National Research Council, 2010b
FIGURE 33
33
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Opportunities to Reduce Other Human- food, and also nitrous oxide and methane from
Produced Warming Agents manure and nitrogen fertilizer. These emissions can
be reduced in many ways, including by employing
There are opportunities to reduce emissions of non-
"precision agriculture" techniques that help farmers
CO2 gases, such as methane, nitrous oxide, and
minimize the over-fertilization practices that lead to
some industrial gases (e.g., hydrofluorocarbons),
emissions, and by improving livestock waste man-
which comprise at least 15% of U.S. greenhouse gas
agement systems.
emissions. Molecule for molecule, these gases are
generally much stronger climate forcing agents than Some shortlived pollutants that are not green-
CO2, although carbon dioxide is the most important house gases also cause warming. One example is
contributor to climate change over the long-term black carbon, or soot, emitted from the burning
because of its abundance and long lifetime. of fossil fuels, biofuels, and biomass (for example,
the dung used in cookstoves in many developing
Some non-CO2 greenhouse gases can be re-
countries). Black carbon can cause strong local or
duced at negative or modest incremental costs. For
regional-scale atmospheric warming where it is
example, reducing methane leaks from oil and gas
emitted. It can also amplify warming in some re-
systems, coal mining, and landfills is cost-effective
gions by leaving a heat-absorbing black coating on
because there is a market for the recovered gas.
otherwise reflective surfaces such as arctic ice and
Reducing methane also improves air quality.
snow. Reducing emissions of these short-lived warm-
The largest overall source of non-CO2 green- ing agents could help ease climate change in the
house emissions is from agriculture, in particular, near term.
methane produced when livestock digest their
What are the choices for preparing for the
impacts of climate change?
A lthough adaptation planning and
response efforts are under way
in a number of states, counties, and
search that focuses on climate change
adaptation actions. In the short term,
adaptation actions most easily de-
communities, much of the nation's ployed include low-cost strategies
experience is in protecting its peo- that offer near-term co-benefits, or
ple, resources, and infrastructure actions that reverse maladaptive
are based on the historic record of policies and practices. In the longer
climate variability during a time of term, more dramatic, higher cost
relatively stable climate. Adaptation to responses may be required. Table 1
climate change calls for a different para- provides a few examples of short-term ac-
digm--one that considers a range of possible tions that might be considered to address some
future climate conditions and associated impacts, of the expected impacts of sea-level rise.
some well outside the realm of past experience. Even though there are still uncertainties regarding
Adaptation efforts are hampered by a lack of solid the exact nature and magnitude of climate change
information about benefits, costs, and the potential impacts, mobilizing now to increase the nation's
and limits of different responses. This is due in part adaptive capacity can be viewed as an insurance pol-
to the diversity of impacts and vulnerabilities across icy against climate change risks. The federal govern-
the United States and the relatively small body of re- ment could play a significant role as a catalyst and
34
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Table 1. Examples of some adaptation options for one expected outcome of sea-level rise.
coordinator of local and regional efforts by providing climate change, the United States can be indirectly
technical and scientific resources, incentives to begin affected by the impacts of climate change occurring
adaptation planning, guidance across jurisdictions, elsewhere in the world. Thus, it is in the country's
a platform to share lessons learned, and support of interest to help enhance the adaptive capacity of
scientific research to expand knowledge of impacts other nations, particularly developing countries that
and adaptation. In addition to the direct impacts of lack resources and expertise.
Why take action if there are still uncertainties
about the risks of climate change?
F
MA K ING C LIMATE C H O IC E S
urther research will never completely eliminate · Some climate change impacts, once manifest-
uncertainties about climate change and its risks, ed, will persist for hundreds or even thousands
given the inherent complexities of the climate sys- of years and will be difficult or impossible to
tem and the many behavioral, economic, and tech- "undo." In contrast, many actions taken to re-
nological factors that are difficult to predict into the spond to climate change could be reversed or
future. However, uncertainty is not a reason for inac- scaled back if they somehow prove to be more
tion, and there are many things we already know stringent than actually needed.
about climate change that we can act on. Reasons · Each day around the world, major investments
for taking action include the following: are being made in equipment and infrastruc-
· The sooner that serious efforts to reduce green- ture that can "lock in" commitments to more
house gas emissions proceed, the lower the risks greenhouse gas emissions for decades to
posed by climate change and the less pressure come. Getting the relevant incentives and poli-
there will be to make larger, more rapid, and cies in place now will provide crucial guidance
potentially more expensive reductions later. for these investment decisions.
35
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· Many actions that could be taken to reduce
vulnerability to climate change impacts are
common sense investments that also will offer
protection against natural climate variations
and extreme events.
The challenge for society is to weigh the risks and
benefits and make wise choices even knowing there
are uncertainties, as is done in so many other realms,
for example, when people buy home insurance. A
valuable framework for supporting climate choices is
an iterative risk management approach. This
refers to a process of systematically identifying risks range of possible futures; and adjusting responses
and possible response options; advancing a portfolio over time to take advantage of new knowledge, in-
of actions that are likely to reduce risks across a formation, and technological capabilities.
Conclusion
R esponding to climate change is about making
choices in the face of risk. Any course of action
carries potential risks and costs; but doing nothing
and other decision makers across the nation; and
those choices will involve numerous value judg-
ments beyond the reach of science. However,
may pose the greatest risk from climate change and robust scientific knowledge and analyses are a
its impacts. America's climate choices will be made crucial foundation for informing choices.
by elected officials, business leaders, individuals,
36
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References
National Research Council, 2010a, Advancing the Science of Climate Change
National Research Council, 2010b, Limiting the Magnitude of Climate Change
National Research Council, 2010c, Adapting to the Impacts of Climate Change
National Research Council, 2011d, Informing an Effective Response to Climate Change
National Research Council, 2010e, Ocean Acidification: A National Strategy to Meet the
Challenges of a Changing Ocean
National Research Council 2011a, Climate Stabilization Targets: Emissions, Concentrations,
and Impacts for Decades to Millennia
National Research Council, 2011c, America's Climate Choices
For more information, contact the Board on Atmospheric Sciences and Climate at
202-334-3512 or visit http://dels.nas.edu/basc. A video based on Part I of this booklet is
available at http://americasclimatechoices.org.
This booklet was prepared by the National Research Council with support from the National Oceanic and
Atmospheric Administration (NOAA). It was developed by Nancy Huddleston and designed by Francesca
Moghari. Special thanks to Ian Kraucunas, Antonio J. Busalacchi, Jr., Edward J. Dunlea, Robert W. Fri,
Laurie Geller, Pamela A. Matson, Damon Matthews, Gerald A. Meehl, Claudia Mengelt, Raymond T.
Pierrehumbert, Kimberly A. Prather, John P. Reisman, and Benjamin D. Santer for their helpful contributions.
Photo Credits
Main cover photo by Michael D. Dudzik; cover thumbnail (bottom) by Fuse; p. 1 by John P. Kelley (Image
Bank); p. 17 by Joe McDonald; p. 19 courtesy United States Geological Survey; p. 20 by Randy Well (Stone);
p. 23, p. 27 by David Haines; p. 30, Jupiter Images (Comstock); p. 36, kali9.
Photo on p. 2 by Mike Waszkiewicz, courtesy National Science Foundation. Nicole Spaulding and Kristin
Schild, students from the University of Maine Climate Change Institute, chip out near-surface ice samples as
part of research into new methods for sampling the record of polar climate change.
© 2012 National Academy of Sciences
About the National Research Council
The National Research Council was organized by the National Academy of Sciences in 1916 to associate
the broad community of science and technology with the Academy's purposes of furthering knowledge
and advising the federal government. The Council has become the principal operating agency of both the
National Academy of Sciences and the National Academy of Engineering and is administered jointly by
both Academies and the Institute of Medicine.
The National Research Council enlists the nation's foremost scientists, engineers, health professionals, and
other experts to serve on committees to address scientific and technical aspects of some of the nation's
most pressing problems. These experts serve pro bono and are screened for conflicts of interest to ensure
that the committee is able to provide impartial and objective advice. Through these committees, the
Academies produce about 200 peer-reviewed reports each year that provide thoughtful analysis and
helpful direction to policymakers and stakeholders.
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How do we know that Earth has warmed? How do we know
that humans are causing greenhouse gas concentrations
to increase? How do we know the current warming trend
isn't caused by the Sun? How do we know that the warming
trend is not caused by natural cycles? How much more
warming can be expected? How is precipitation expected to
change? How will sea ice and snow be affected? How will
coastlines be affected? How will ecosystems be affected?
How will agriculture and food production be affected? How
does science inform the response to climate change?
