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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
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
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
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
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
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
· 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
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.
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?