Notes and References

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1. The analyses in this report focus primarily on energy-related carbon dioxide (CO2) emissions, which constitute roughly 83 percent of total U.S. greenhouse gas emissions (U.S. Environmental Protection Agency [EPA], Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009. EPA 430-R-11-005 [Washington, D.C.: EPA, 2011, available at, accessed March 2, 2011]). As discussed in Chapter 1, however, there are other long-lived greenhouse gases, as well as shorter-lived gas and particulate compounds, that contribute to climate change and offer mitigation opportunities.


1. United Nations Framework Convention on Climate Change (UNFCCC), i.e., the "Rio declaration" ratified by the United States in 1992.

2. EPA, Draft Inventory.

4. J. M. Broder, "Emissions fell in 2009, showing impact of recession," (New York Times, Feb 16, 2011, available at http://, accessed April 11, 2011).

5. Energy Information Administration (EIA), International Energy Outlook, Report #:D0E/EIA-0484(2010) (Washington, D.C.: U.S. Department of Energy, 2010, available at, accessed March 4, 2011).

6. S. J. Davis, K. Calderia, and D. Matthews, "Future C02 emissions and climate change from existing energy infrastructure" (Science 10 329[5997]:1330-1333, 2010, doi: 10.1126/science.1188566).

7. International Energy Agency. 2010. World Energy Outlook2010 (Paris, France: International Energy Agency, 2010).


9. Massachusetts v. Environmental Protection Agency, 549 U.S. 497. 2007 ( opinions/06pdf/05-1120.pdf).


11. See: A. J. Hoffman, "Climate change strategy: The business logic behind voluntary greenhouse gas reductions" (California Management Review 47[3]:21-46, 2005); NRC, America's Climate Choices: Informing Effective Decisions on Climate Change (Washington, D.C.: National Academies Press, 2010), Table 2.3; and reports of the World Business Council on Sustainable Development (, the U.S. Climate Action Partnership (http://www., the American Energy Innovation Council (, and the Business Environmental Leadership Council (


13. A renewable portfolio standard (RPS) mandates the use of a given percentage of renewable energy sources in an overall energy mix for example in the electricity sector.

14.; and for a comprehensive map/listing of relevant state efforts, see:


16. For example, King County, Washington, worked with the Climate Impacts Group at the University of Washington and ICLEI: Local Governments for Sustainability to produce a handbook in 2007, Preparing for Climate Change: A Guidebook for Local, Regional, and State Governments.


17. Department of Defense, Quadrennial Defense Review Report (Washington, D.C.: U.S. Department of Defense, 2010, available at, accessed March 1, 2011); D. C. Blair, Annual Threat Assessment of the U.S. Intelligence Community. Statement for the Record to the Senate Select Committee on Intelligence (2010, available at, accessed February 28, 2011); NRC, Advancing the Science of Climate Change (Washington, D.C.: National Academies Press, 2010), Chapter 15.

18. Center for Climate Strategies, Impacts of Comprehensive Climate and Energy Policy Options on the U.S. Economy (Washington, D.C.: Johns Hopkins University, 2010, available at energy-policy-report/, accessed March 1, 2011); N. M . Bianco and F. T. Litz, Reducing Greenhouse Gas Emissions in the United States: Using Existing Federal Authorities and State Action (Washington, D.C.: World Resources Institute, 2010, available at, accessed March 8, 2011).

19. M. Betsill and H. Bulkeley, "Cities and the multilevel governance of global climate change" (Global Governance 12 [2]:141-159, 2006).

20. See, for example, E. Ostrom, "A multi-scale approach to coping with climate change and other collective action problems" (Solutions 1:27-36, 2010).


1. For a historical overview of the science of climate change, see S. R. Weart, The Discovery of Global Warming (Cambridge, MA: Harvard University Press, 2008).

2. According to IPCC (Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, eds. S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor, and H. L. Miller [Cambridge, UK: Cambridge University Press, 2007]): "Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level."

3. The temperature of the lower atmosphere is measured directly by instruments mounted on weather balloons (see, e.g., M. P. McCarthy, H. A. Titchner, P. W. Thorne, S. F. B. Tett, L. Haimberger, and D. E. Parker, "Assessing bias and uncertainty in the HadAT-adjusted radiosonde climate record" [Journal of Climate 21(4):817-832, 2008]) and indirectly by satellites that measure the energy radiated upward from the Earth at specific wavelengths (J. R. Christy, R. W. Spencer, W. D. Braswell, "MSU tropospheric temperatures: Dataset construction and radiosonde comparisons" [Journal of Atmospheric and Oceanic Technology 17:1153-1170, 2000]; J. R. Christy, R. W. Spencer, W. B. Norris, and W. D. Braswell, "Error estimates of version 5.0 of MSUAMSU bulk atmospheric temperatures" [Journal of Atmospheric and Oceanic Technology 20:613-629, 2003]; C. A. Mears and F. J. Wentz,"Construction of the remote sensing systems V3.2 atmospheric temperature records from the MSU and AMSU microwave sounders" [Journal of Atmospheric and Oceanic Technology 26:1040-1056, 2009, doi: 10.1175/2008JTECHA1176.1]). Trends in these data have been assessed in detail by the U. S. Climate Change Science Program (CCSP (Temperature Trends in the Lower Atmosphere:Steps for Understanding and Reconciling Differences, Synthesis and Assessment Product 1.1, eds. T. R. Karl, S. J. Hassol, C. D. Miller, and W. L. Murray [Washington, D.C.: National Oceanic and Atmospheric Administration, 2006]) and the IPCC (Climate Change2007 WG1, Summary for Policymakers).

4. The warming of the uppermost 700 meters of the world oceans is documented in S. J. Levitus, I. Antonov, T. P. Boyer, R. A. Locarnini, H. E. Garcia, and A. V. Mishonov, "Global ocean heat content 1955-2008 in light of recently revealed instrumentation problems" (Geophysical Research Letters 36:L07608, 2009).

5. According to the IPCC (Climate Change 2007, Ch9): "anthropogenic forcing has likely contributed to recent decreases in Arctic sea ice extent and to glacier retreat."

6. IPCC (Climate Change2007 WG1, Ch9) concludes "It is likely that anthropogenic forcing has contributed to the general warming observed in the upper several hundred meters of the ocean during the latter half of the 20th century."

7. According to IPCC (Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, eds. M. L. Parry, O. F. Canziani, J. P. Palutikof, P. J. van der Linden, and C. E. Hanson [Cambridge, UK: Cambridge University Press, 2007]): "There is very high confidence [about 8 out of 10 chance of being correct] . . . that recent warming is strongly affecting terrestrial biological systems" and "high confidence, based on substantial new evidence, that observed changes in marine and freshwater biological systems are associated with rising water temperatures, as well as related changes in ice cover, salinity, oxygen levels and circulation."

8. According to IPCC (Climate Change 2007 WG1, Summary for Policymakers): "Most of the observed increase in global average temperatures since the mid-20th century is very likely [greater than 90 percent likelihood] due to the observed increase in anthropogenic greenhouse gas concentrations."

9. D. Luthi, M. Le Floch, B. Bereiter, T. Blunier, J.-M. Barnola, U. Siegenthaler, D. Raynaud, J. Jouzel, H. Fischer, K. Kawamura, and T. F. Stocker, "High-resolution carbon dioxide concentration record 650,000-800,000 years before present" (Nature 453[7193]:379-382, 2008, doi:10.1038/nature06949).

10. IPCC (Climate Change2007 WG1, Summary for Policymakers): "The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial period results from fossil fuel use, with land-use change providing another significant but smaller contribution." This statement is based in part on the fossil fuel emissions data in Figure 1.2; in part on estimates of the other sources as "sinks" of atmospheric carbon dioxide like those provided by the Global Carbon Project (Le Quere, C. M. R. Raupach, J. G. Canadell, G. Marland, L. Bopp, P. Ciais, T. J. Conway, S. C. Doney, R. A. Feely, P. Foster, P. Friedlingstein, K. Gurney, R. A. Houghton, J. I. House, C. Huntingford,

P. E. Levy, M. R. Lomas, J. Majkut, N. Metzl, J. P. Ometto, G. P. Peters, I. C. Prentice, J. T. Randerson, S. W. Running, J. L. Sarmiento, U. Schuster, S. Sitch, T. Takahashi, N. Viovy, G. R. van der Werf, and F. I. Woodward,"Trends in the sources and sinks of carbon dioxide" [Nature Geoscience 2, 2009, doi: 10.1038/ngeo689]), which indicate that deforestation and other land use changes currently contribute about 12% of total human-induced CO2 emissions; and in part on the chemical "fingerprints" of CO2 and other gases in the atmosphere, which can only be explained by the burning of coal, oil, and natural gas (R. F. Keeling, S. C. Piper, A. F. Bollenbacher and J. S. Walker, "Atmospheric CO2 records from sites in the SIO air sampling network," in Trends: A Compendium of Data on Global Change (Oak Ridge, TN: Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, 2009).

11. Methane comes from fossil fuel and biomass burning, natural gas management, animal husbandry, rice cultivation, and waste management (S. Houweling, T. Rockmann, I. Aben, F. Keppler, M. Krol, J. F. Meirink, E. J. Dlugokencky, and C. Frankenberg, "Atmospheric constraints on global emissions of methane from plants" [Geophysical Research Letters 33:L15821, 2006, doi:10.1029/2006GL026162]). The atmospheric concentration of methane rose sharply through the late 1970s before leveling off at about two-and-a-half times its estimated pre-industrial concentration. Methane levels have risen slightly in each of the past few years (E. J. Dlugokencky, L. Bruhwiler, J. W. C. White, L. K. Emmons, P. C. Novelli, S. A. Montzka, K. A. Masarie, P. M. Lang, A. M. Crotwell, J. B. Miller, and L. V. Gatti, "Observational constraints on recent increases in the atmospheric CH4 burden" [Geophysical Research Letters 36:L18803, 2009]) but the reasons for the changes are not completely clear. Nitrous oxide concentrations are steadily increasing primarily as a result of agricultural activities (especially the application of chemical fertilizers), but also a byproduct of fossil fuel combustion and certain industrial process. Halogenated gases include chlorofluorocar-bons (CFCs), hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride, all of which are produced primarily by industrial processes. Many of these compounds also contribute to the depletion of ozone in the stratosphere, which is a related but largely separate environmental problem from climate change (see, e.g., CCSP, Trends in Emissions of Ozone-Depleting Substances, Ozone Layer Recovery, and Implications for Ultraviolet Radiation Exposure, Synthesis and Assessment Product 2.4 by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research, eds. A. R. Ravishankara, M. J. Kurylo, and C. A. Ennis [Asheville, NC: National Oceanic and Atmospheric Administration, 2008]). Water vapor is also an important greenhouse gas, but its concentration in the lower atmosphere is controlled by the rates of evaporation and precipitation, which are natural processes that are much more strongly influenced by changes in atmospheric temperature and circulation than by human activities directly.


12. T. P. Barnett, D. W. Pierce, K. M. AchutaRao, P. J. Gleckler, B. D. Santer, J. M. Gregory, and W. M. Washington ("Penetration of human-induced warming into the world's oceans" [Science 309(5732):284-287, 2005, doi: 10.1126/sci-ence.1112418]) conclude that the observed warming trend cannot be explained by the release of heat stored in the deep ocean or other climate system components, while IPCC (Climate Change2007 WG1) concludes that "it is extremely unlikely (<5%) that the global pattern of warming during the past half century can be explained without external forcing, and very unlikely (<10%) that it is due to known natural external causes alone." The latter conclusion is based in part on the fact that models of the climate system are able to reproduce the observed spatial and temporal pattern of warming when human-induced GHG and aerosol emissions are included in the simulation, but not when only natural climate forcing factors are included (IPCC, Climate Change2007 WG1, Ch8). Reconstructions of solar activity based on historical records and other sources suggest that the amount of energy reaching Earth from the sun may have increased slightly during the late 19th and early 20th century, possibly contributing to some of the warming observed in the first few decades of the 20th century, but satellite observations show definitively that solar output has not increased overall during the last 30 years (J. L. Lean and T. N. Woods,"Solar total and spectral irradiance: Measurements and models," in Heliophysics: Evolving Solar Physics and the Climates of Earth and Space, eds. C. J. Schrijver and G. Siscoe (Cambridge, UK: Cambridge University Press, 2010).

13. According to USGCRP (Global Climate Change Impacts in the United States, eds. T. R. Karl, J. M. Melillo, and T. C. Peterson [Cambridge, U.K.: Cambridge University Press, 2009]): ". . . . scientists have established causal links between human activities and the changes in snowpack, maximum and minimum temperature, and the seasonal timing of runoff over mountainous regions of the western United States" (see also T. P. Barnett, D. W. Pierce, H. G. Hidalgo, C. Bonfils, B. D. Santer, T. Das, G. Bala, A. W. Wood, T. Nozawa, A. A. Mirin, D. R. Cayan, and M. D. Dettinger, "Human-induced changes in the hydrology of the western United States" [Science 319(5866):1080-1083, 2008]; D. W. Pierce, T. P. Barnett, H. G. Hidalgo, T. Das, C. Bonfils, B. D. Santer, G. Bala, M. D. Dettinger, D. R. Cayan, A. Mirin,

A. W. Wood, and T. Nozawa, "Attribution of declining western U.S. snowpack to human effects" [Journal of Climate 21(23):6425-6444, 2008]; and C. Bonfils, B. D. Santer, D. W. Pierce, H. G. Hidalgo, G. Bala, T. Das, T. P. Barnett, D. R. Cayan, C. Doutriaux, A. W. Wood, A. Mirin, and T. Nozawa, "Detection and attribution of temperature changes in the mountainous western United States" [Journal of Climate 21(23):6404-6424, 2008]).

14. According to IPCC (Climate Change 2007 WG1, Summary for Policymakers): "At continental, regional and ocean basin scales, numerous long-term changes in climate have been observed. These include changes in Arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns, and aspects of extreme weather including droughts, heavy precipitation, heat waves, and the intensity of tropical cyclones."

15. E.g., J. Oerlemans, "Extracting a climate signal from 169 glacier records" (Science 308[5722]:675-677, 2005); R. Thomas, E. Frederick, W. Krabill, S. Manizade, and C. Martin, "Progressive increase in ice loss from Greenland" (Geophysical Research Letters 33[10], 2006); E. Rignot, J. E. Box, E. Burgess, and E. Hanna, "Mass balance of the Greenland ice sheet from 1958 to 2007" (Geophysical Research Letters 35[20], 2008); I. Velicogna, "Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE" (Geophysical Research Letters 36, 2009).

16. IPCC (Climate Change 2007 WG1, Ch5), based on data from, J. A. Church and N. J. White, "A 20th century acceleration in global sea-level rise" (Geophysical Research Letters 33[1], 2006); S. J. Holgate and P. L. Woodworth,"Evidence for enhanced coastal sea level rise during the 1990s" (Geophysical Research Letters 31[7]:L07305, 2004); and E. W. Leuliette, R. S. Nerem, and G. T. Mitchum, "Calibration of TOPEX/Poseidon and Jason altimeter data to construct a continuous record of mean sea level change" (Marine Geodesy 27[1-2]:79-94, 2004).

17. IPCC (Climate Change2007 WG1, Ch4) update of R. D. Brown, "Northern Hemisphere snow cover variability and change, 1915-97" (Journal of Climate 13:2339-2355, 2000).

18. S. K. Min, X. Zhang, F. W. Zwiers, and T. Agnew ("Human influence on Arctic sea ice detectable from early 1990s onwards" [GeophysicalResearch Letters 35(21), 2008]) conclude that the overall decline in Arctic sea ice since 1979 is very likely due to human-induced warming; discussion of recent sea ice trends (which have been attributed to changes in wind patterns as well as to warming) can also be found in J. E. Overland, M. Wang, and S. Salo, "The recent Arctic warm period" (Tellus Series A—Dynamic Meteorology and Oceanography 60[4]:589-597, 2008); X. D. Zhang, A. Sorteberg, J. Zhang, R. Gerdes, and J. C. Comiso, "Recent radical shifts of atmospheric circulations and rapid changes in Arctic climate system" (Geophysical Research Letters 35[22], 2008); J. Stroeve, M. M. Holland,

W. Meier, T. Scambos, and M. Serreze, "Arctic sea ice decline: faster than forecast" (Geophysical Research Letters 34[9]:L09501, 2007, doi:10.1029/2007GL029703); and M. C., Serreze, M. M. Holland, and J. Stroeve, "Perspectives on the Arctic's shrinking sea-ice cover" (Science 315[5818]:1533-1536, 2007, doi:10.1126/science.1139426). In the Southern Hemisphere, sea ice cover has actually increased slightly over the past several decades; this trend has been attributed to changes in atmospheric circulation associated with stratospheric ozone depletion (D. J. Cavalieri and C. L. Parkinson, "Antarctic sea ice variability and trends, 1979-2006" [Journal of Geophysical Research-Oceans 113(C7):C07004, 2008]; J. Turner, J. C. Comiso, G. J. Marshall, T. A. Lachlan-Cope, T. Bracegirdle, T. Maksym, M. P. Meredith, Z. M. Wang, and A. Orr, "Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent" [Geophysical Research Letters 36:L08502, 2009, doi: 10.1029/2009GL037524]).

19. According to IPCC (Climate Change 2007 WG2, Summary for Policymakers): "Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases" and "a global assessment of data since 1970 has shown it is likely (>66% likelihood) that anthropogenic warming has had a discernible influence on many physical and biological systems."

20. According to IPCC (Climate Change 2007 WG7,Ch4): "The maximum extent of seasonally frozen ground has decreased by about 7% in the Northern Hemisphere from 1901 to 2002, with a decrease in spring of up to 15%." There are substantial regional differences in permafrost warming/melting; permafrost trends in Russia, for example, are documented by H. J. Akerman and M. Johansson, "Thawing permafrost and thicker active layers in sub-arctic Sweden" (Permafrost and Periglacial Processes 19[3]:279-292, 2008); V. E. Romanovsky, T. S. Sazonova, V. T. Balobaev, N. I. Shender, and D. O. Sergueev, "Past and recent changes in air and permafrost temperatures in eastern Siberia" (Global and Planetary Change 56[3-4]:399-413, 2007), and T. Osterkamp, "Characteristics of the recent warming of permafrost in Alaska" (Journal of Geophysical Research 112:F02S02, 2007, doi:10.1029/2006JF000578).

21. The IPCC (Climate Change2007 WG1) report that averaged over all available data, the freezing period of lake and river ice has decreased by 12 days over the past 150 years.

22. As discussed in USGCRP (Global Climate Change Impacts, page 85): "As the carbon dioxide concentration in the air increases, more carbon dioxide is absorbed into the world's oceans, leading to their acidification. This makes less calcium carbonate available for corals and other sea life to build their skeletons and shells. If carbon dioxide concentrations continue to rise and the resulting acidification proceeds, eventually, corals and other ocean life that rely on calcium carbonate will not be able to build these skeletons and shells at all. The implications of such extreme changes in ocean ecosystems are not clear, but there is now evidence that . . . acidification is already occurring. See also NRC, Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean (Washington, D.C.: National Academies Press, 2010); and NRC, Advancing the Science.

23. USGCRP Global Climate Change Impacts.

24. USGCRP (Global Climate Change Impacts, pages 28 and 30), based on U.S. Historical Climate Network data from NOAA/NCDC (M. J. Menne and C. N. Williams, Jr., "Homogenization of temperature series via pairwise comparisons" (Journal of Climate 22:1700-1717, 2009),

25. USGCRP (Global Climate Change Impacts, pages 37 and 149); See also CCSP, Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region, Synthesis and Assessment Product 4.1 by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research, ed. J. G. Titus, coordinating lead author; E. K. Anderson, D. R. Cahoon, S. Gill, R. E.Thieler, and J. S.Williams, lead authors (Washington, D.C.: U.S. Environmental Protection Agency, 2009) and CCSP, The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States, Synthesis and Assessment Product 4.3 by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research, eds. P. Backlund, A. Janetos, D. Schimel, J. Hatfield, K. Boote, P. Fay, L. Hahn, C. Izaurralde, B. A. Kimball, T. Mader, J. Morgan, D. Ort, W. Polley, A. Thomson, D. Wolfe, M. G. Ryan, S. R. Archer, R. Birdsey, C. Dahm, L. Heath, J. Hicke, D. Hollinger, T. Huxman,G. Okin, R. Oren, J. Randerson, W. Schlesinger, D. Lettenmaier, D. Major, L. Poff, S. Running, L. Hansen, D. Inouye, B. P. Kelly, L. Meyerson, B. Peterson, and R. Shaw (Washington, D.C.: National Oceanic and Atmospheric Administration, 2008).

26. USGCRP (Global Climate Change Impacts, page 141); see also CCSP, SAP 4.3; Osterkamp, Characteristics; and A. Instanes, O. Anisimov, L. Brigham, D. Goering, L. N. Khrustalev, B. Ladanyi, and J. O. Larsen, "Infrastructure: buildings,


support systems, and industrial facilities,"pp. 907-944 in Arctic Climate Impact Assessment (Cambridge, UK: Cambridge University Press, 2005).

27. USGCRP (Global Climate Change Impacts, page 45); see also B. C. Bates, Z. W. Kundzewicz, S. Wu, and J. P. Palutikof, eds., Climate Change and Water, Technical paper of the Intergovernmental Panel on Climate Change (Geneva, Switzerland: IPCC Secretariat, 2008); P. Mote, A. Hamlet, and E. Salathe, "Has spring snowpack declined in the Washington Cascades?" (Hydrology and Earth System Sciences 12[1]:193-206.2008); S. Feng, and Q. Hu,"Changes in winter snowfall/precipitation ratio in the contiguous United States" (Journal of Geophysical Research 112:D15109, 2007, doi:10.1029/2007JD008397); I. T. Stewart, D. R. Cayan, and M. D. Dettinger, "Changes toward earlier streamflow timing across western North America" (Journal of Climate,18:1136-1155, 2005).

28. USGCRP (Global Climate Change Impacts, page 32) reports that "The amount of rain falling in the heaviest downpours has increased approximately 20 percent on average in the past century" in the United States, and that this increase accounts for most of the overall precipitation trend. K. E. Kunkel, P. D. Bromirski, H. E. Brooks, T. Cavazos, A. V. Douglas, D. R. Easterling, K. A. Emanuel, P. Ya. Groisman, G. J. Holland, T. R. Knutson, J. P. Kossin, P. D. Komar, D. H. Levinson, and R. L. Smith "Observed changes in weather and climate extremes," in Weather and Climate Extremes in a Changing Climate. Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands, eds. T. R. Karl,

G. A. Meehl, C. D. Miller, S. J. Hassol, A. M. Waple, and W. L. Murray (Washington, D.C.: U.S. Climate Change Science Program, 2008), based on a number of sources, report that "Extreme precipitation episodes (heavy downpours) have become more frequent and more intense in recent decades than at any other time in the historical record, and account for a larger percentage of total precipitation."

29. USGCRP (Global Climate Change Impacts, page 33), based on Kunkel et al., "Observed changes," pages 42-46. See also A. Dai, K. E. Trenberth, and T. Qian, "A global data set of Palmer Drought Severity Index for 1870-2002: Relationship with soil moisture and effects of surface warming" (Journal of Hydrometeorology 5(6):1117-1130, 2004).

30. USGCRP (Global Climate Change Impacts, page 82); see also CCSP SAP 4.3; J. S. Littell, D. McKenzie, D. L. Peterson, and A. L. Westerling, "Climate and wildfire area burned in western U. S. ecoprovinces, 1916-2003" (Ecological Applications 19[4]:1003-1021, 2009).

31. Probabilities are not attached to particular socioeconomic and emissions scenarios, but there is high confidence that realized future concentrations/radiative forcing resulting from anthropogenic activities will very likely fall within the range of estimates reflected in recent work establishing the new Representative Concentration Pathways. Note that this range does not include additional forcing possible from feedbacks.

32. Climate (or Earth system) models simulate the temporal evolution of the atmosphere, ocean, land surface, and other aspects of the climate system under certain assumptions and boundary conditions (such as, for example, different scenarios of future GHG emissions). These models are based on the fundamental laws of physics and chemistry, are calibrated and tested using observations of current and past climate change, and reflect current scientific understanding of relevant climate processes. However, certain features of the Earth system, such as clouds and the global carbon cycle, are either incompletely understood or cannot be fully resolved by current models, and so their effects must be approximated. As a result, for a given emissions scenario different models will predict somewhat different magnitude and details of future climate change.

33. Vulnerability is defined here as the degree to which a system is susceptible to, or unable to cope with, adverse effects of climate change. Vulnerability is a function of the character, magnitude, and rate of climate variation to which a system is exposed, its sensitivity, and its adaptive capacity.

34. IPCC (Climate Change2007 WG1, Ch. 10). Note that IPCC chose not to assign a likelihood to this range because much of the variation comes from different assumptions about how the world will respond to climate change.

35. See, e.g., L. Tomassini, R. Knutti, G. Plattner, D. van Vuuren, T. Stocker, R. Howarth, and M. Borsuk, "Uncertainty and risk in climate projections for the 21st century: Comparing mitigation to non-intervention scenarios" (Climatic Change 103[3-4]:399-422, 2010, DOI 10.1007/s10584-009-9763-3). Also note that the scenarios on which these projections of future climate change are based do not actually reflect how policy interventions might influence future GHG emissions—they are rather illustrations of how climate change might evolve in the absence of global actions to reduce emissions. However, to the extent that the scenarios depicted in Figure 2.3 mirror emissions reductions that might be achieved through policy actions, they can be thought of as rough proxies for the temperature and other climate changes expected under increasingly aggressive GHG emission reductions. As discussed below and in further detail in two of the ACC panel reports (NRC, Advancing the Science and NRC, Limiting the Magnitude of Climate Change [Washington, D.C.: National Academies Press, 2010]), recent scenario development efforts do include consideration of the socioeconomic, technological, and policy aspects of alternative GHG trajectories. These efforts have also focused on developing GHG trajectories in a more integrated and iterative manner with climate model projections and assessments of current and future climate impacts.(e.g., CCSP, Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations, Sub-report 2.1A of Synthesis and Assessment Product 2.1 by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research, eds. L. Clarke, J. Edmonds, H. Jacoby, H. Pitcher, J. Reilly, and R. Richels [Washington, D.C.: Department of Energy, Office of Biological and Environmental Research, 2007]; L. Clarke, J. Edmonds, V. Krey, R. Richels, S. Rose, and M. Tavoni, "International climate policy architectures: Overview of the EMF 22 International Scenarios" [Energy Economics 31(Supplement 2):S64-S81, 2009], R. H. Moss, J. A. Edmonds, K. A. Hibbard, M. R. Manning, S. K. Rose, D. P. Van Vuuren, T. R. Carter, S. Emori, M. Kainuma, T. Kram, G. A. Meehl, J. F. B. Mitchell, N. Nakicenovic, K. Riahi, S. J. Smith, R. J. Stouffer, A. M. Thomson, J. P. Weyant, and T. J. Wilbanks, "The next generation of scenarios for climate change research and assessment" [Nature 463(7282):747-756, 2010]).

36. NRC, Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia (Washington, D.C.: National Academies Press, 2010).

38. IPCC (Climate Change2007 WG1, Summary for Policymakers): "It is very likely [greater than 90% likelihood] that hot extremes, heat waves, and heavy precipitation events will continue to become more frequent."

39. R. J. Nicholls and A. Cazenave, "Sea-level rise and its impact on coastal zones" (Science 328[5985]:1517-1520, 2010, doi:10.1126/science.1185782); NRC, Advancing the Science, pages 191-193).

40. USGCRP (Global Climate Change Impacts, pages 62-63 and references therein).

41. S. Solomon, G.-K. Plattner, R. Knutti, and P. Friedlingstein, "Irreversible climate change due to carbon dioxide emissions" (Proceedings of the National Academy of Sciences 106:1707-1709, 2009).

42. IPCC (Climate Change2007 WG2, Summary for Policymakers) and also S. C. Doney, V. J. Fabry, R. A. Feely, and J. A. Kleypas, "Ocean acidification: The other CO2 problem" (Annual Review of Marine Science 1:169-192, 2009); L. Cao, and K. Caldeira, "Atmospheric CO2 stabilization and ocean acidification" (GeophysicalResearch Letters 35:L19609, 2008); J. Silverman, B. Lazar, L. Cao, K. Caldeira, and J. Erez, "Coral reefs may start dissolving when atmospheric CO2 doubles" (Geophysical Research Letters 36:L05606, 2009, doi:10.1029/2008GL036282).

43. USGCRP (Global Climate Change Impacts, pages 84-85)

44. Ocean acidification also poses significant risks to a wide range of other marine organisms (NRC, Ocean Acidification).

45. USGCRP (Global Climate Change Impacts, pages 47 and 83 and references therein).

47. Ibid., (page 83), see also A. L. Westerling and B. P. Bryant, "Climate change and wildfire in California" (Climatic Change 87[1]:1-19, 2008, doi:10.1007/s10584-007-9363-z); NRC, Stabilization Targets.

48. NRC, Ecological Impacts of Climate Change (Washington, D.C.: National Academies Press, 2008); IPCC, Climate Change 2007 WG2, Ch. 4.

49. USGCRP (Global Climate Change Impacts, pages 89-98).

50. Center for Integrative Environmental Research, The US Economic Impacts of Climate Change and the Costs of Inaction: A Review and Assessment by the Center for Integrative Environmental Research at the University of Maryland (College Park, MD: University of Maryland, 2007, available at: http://, accessed March 1, 2011); Congressional Budget Office (CBO), Potential Impacts of Climate Change in the United States (Washington, D.C.: Congressional Budget Office, 2009, available at, accessed March 1, 2011).



1. For additional discussion, see Solomon et al., "Irreversible climate change" and NRC, Stabilization Targets.

2. It is estimated that 80-90 percent of the heating associated with GHG emissions over the past 50 years has gone into raising the temperature of the world's oceans (K. E. Trenberth and J. T. Fasullo, "Tracking Earth's energy" Science 328[5976]:316-317.2010). Also, it is estimated that even if atmospheric GHG concentrations could be immediately stabilized, an additional 0.1°C of warming per decade would be experienced over the next several decades (IPCC, Climate Change 2007 WG1).

3. See Solomon et al., "Irreversible climate change"; NRC, Stabilization Targets; NRC, Ocean Acidification; M. Meinshausen, N. Meinshausen, W. Hare, S. C. B. Raper, K. Frieler, R. Knutti, D. J. Frame, and M. R. Allen, "Greenhouse-gas emission targets for limiting global warming to 2 degrees Celsius" (Nature 458[7242]:1158-U1196, 2009, doi: 10.1038/nature08017).

4. See NRC, Limiting the Magnitude, p.114.

5. For critical analyses related to allocating emissions reduction responsibility, including views on how to implement the UNFCCC principle of "common but differentiated responsibilities," see S. Caney, "Cosmopolitan justice, responsibility, and global climate change" (Leiden Journal of International Law 18[4]:747-775, 2005) and E. A. Page, "Distributing the burdens of climate change." (Environmental Politics 17[4]:556-575, 2008). For a recent proposal for allocating responsibilities among individuals, see S. Chakravarty, A. Chikkatur, H. de Coninck, S. Pacala, R. Socolow, and M. Tavoni, "Sharing global CO2 emission reductions among one billion high emitters" (Proceedings of the National Academy of Sciences 106[29]:11884-11888, 2009).

6. See NRC, Limiting the Magnitude for detailed discussion about the magnitude of these sorts of co-benefits.

7. Discussed further in NRC, Advancing the Science, Chapter 17, and NRC, Limiting the Magnitude, Chapter 2).

8. See NRC, America's Climate Choices: Adapting to the Impacts of Climate Change. Washington, D.C.: National Academies Press, 2010; and IPCC, Climate Change2007 WG2 for additional details.

9. See NRC, Advancing the Science, Chapter 17.

10. For instance, G. F. Nemet, T. Holloway, and P. Meier, "Implications of incorporating air-quality co-benefits into climate change policy making" (Environmental Research Letters 5, 2010) surveyed 37 studies of the economic benefit of air pollutant reductions that accompanied climate change mitigation efforts (given in dollars per ton of CO2 avoided, in 2008 dollars). For developed countries, benefits ranged from $2-128 / tCO2. For developing counties, the range was $27-196 / tCO2. Developing countries generally have much higher levels of air pollution, and thus the incremental benefits of pollution mitigation are much greater.

11. T. Searchinger, R. Heimlich, R. A. Houghton, F. Dong, A. Elobeid, J. Fabiosa, S. Tokgoz, D. Hayes, and T. H. Yu, "Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change" (Science 319[5867]:1238-1240, 2008); D. A. Landis, M. M. Gardiner, W. van der Werf, and S. M. Swinton, "Increasing corn for biofuel production reduces biocontrol services in agricultural landscapes" (Proceedings of the National Academy of Sciences 105[51]:20552-20557, 2008).

12. This topic is addressed at length in NRC, Informing Effective Decisions and in NRC, Facilitating Climate Change Responses: A Report of Two Workshops on Knowledge from the Social and Behavioral Sciences (Washington, D.C.: National Academies Press, 2010), Chapter 1.

13. C. Keller, M. Siegrist, and H. Gutscher, "The role of the affect and availability heuristic in risk communication" (Risk Analysis 26:631-639, 2006); R. Hertwig, G. Barron, E. U. Weber, and I. Erev, "Decisions from experience and the effect of rare events" (Psychological Science 15:534-539 2004); and E. U. Weber and P. C. Stern, "Public understanding of climate change in the United States" (American Psychologist, 2011, in press).

14. A. Bostrom, M. G. Morgan, B. Fischhoff, and D. Read, "What do people know about global climate change? 1. Mental models" (Risk Analysis 14:959-970, 1994); T. W. Reynolds, A. Bostrom, D. Read, and M. G. Morgan, "Now what do people know about global climate change? Survey studies of educated laypeople" (RiskAnalysis 30(10):1520-1538, 2010).

15. For instance, Sterman and Booth-Sweeney ("Understanding public complacency about climate change: Adults' mental models of climate change violate conservation of matter" [Climatic Change 80:213-238, 2007]) found that

63% of a sample of MIT graduate students believed that atmospheric CO2 concentrations can be stabilized under a scenario where the amount of CO2 emitted to the atmosphere exceeded the amount being removed from the atmosphere; A. Leiserowitz, N. Smith, and J. R Marlon, Americans' Knowledge of Climate Change (Yale Project on Climate Change Communication. New Haven, Connecticut: Yale University, 2010).

16. NRC, Facilitating Climate Change Responses; Weber and Stern, "Public understanding."

17. See, e.g., R. E. Dunlap and A. M. McCright, 2008. "Widening gap: Republican and Democratic views on climate change" (Environment 50:26-35, 2008); R. E. Dunlap and A. M. McCright, "Climate change denial: Sources, actors, and strategies." in Routledge Handbook of Climate Change and Society, ed. C. Lever-Tracy (New York: Routledge, 2010); M. Hulme, Why We Disagree About Climate Change: Understanding Controversy, Inaction and Opportunity (Cambridge, UK: Cambridge University Press, 2009); N. Oreskes and E. M. Conway, Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Global Warming. (New York: Bloomsbury Press, 2010).

18. See, e.g., National Intelligence Council, Global Trends 2025: A Transformed World (Washington, D.C.: US Government Printing Office, 2008, available at:, accessed March 3, 2011, 2008); CNA Corporation, National Security and the Threat of Climate Change (Alexandria, VA: The CNA Corporation, 2007, available at:, accessed March 1, 2011).

19. J. Hansen, M. Sato, R. Ruedy, P. Kharecha, A. Lacis1, R. Miller, L. Nazarenko, K. Lo, G. A. Schmidt, G. Russell, I. Aleinov, S. Bauer, E. Baum, B. Cairns, V. Canuto, M. Chandler, Y. Cheng, A. Cohen, A. Del Genio, G. Faluvegi, E. Fleming, A. Friend, T. Hall, C. Jackman, J. Jonas, M. Kelley, N. Y. Kiang, D. Koch, G. Labow, J. Lerner, S. Menon, T. Novakov, V. Oinas, Ja. Perlwitz, Ju. Perlwitz, D. Rind, A. Romanou, R. Schmunk, D. Shindell, P. Stone, S. Sun, D. Streets, N. Tausnev, D. Thresher, N. Unger, M. Yao, and S. Zhang, Dangerous human-made interference with climate: A GISS model study" (Atmospheric Chemistry and Physics 7:2287-2312, 2007); Proceedings of the National Academy of Sciences, Tipping Elements in Earth Systems Special Feature (PNAS 106[49]:20561, 2009).

20. M. G. Morgan, M. Kandlikar, J. Risbey, and H. Dowlatabadi, "Why conventional tools for policy analysis are often inadequate for problems of global change" (Climatic Change 41:271-281, 1999).


1. See also NRC, Informing Decisions in a Changing Climate (Washington, D.C.: National Academies Press, 2009) and NRC, Informing Effective Decisions.

2. C. E. Lindblom, "The science of 'muddling through'" (Public Administration Review 19[2], 1959, available at http://, accessed March 3, 2011).

3. The United Nations Educational, Scientific and Cultural Organization (UNESCO) The Precautionary Principle. World Commission on the Ethics of Scientific Knowledge and Technology (Paris: UNESCO, 2005, available at http://unesdoc., accessed March 4, 2011) defines the precautionary principle as follows: Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost effective measures to prevent environmental degradation.

4. C. R. Sunstein, Laws of Fear: Beyond the Precautionary Principle (New York: Cambridge University Press, 2005); R. J. Lempert and M. T. Collins, "Managing the risk of uncertain threshold responses: Comparison of robust, optimum, and precautionary approaches" (Risk Analysis 27[4]:1009-1026, 2007).

5. See, e.g., W. D. Nordhaus, A Question of Balance. Weighing the Options on Global Warming Policies (New Haven. CT: Yale University Press, 2008); R. S. J. Tol, "Equitable cost-benefit analysis of climate change" (Ecological Economics 36(1):71-85, 2001); N. Stern, Stern Review on the Economics of Climate Change (London, U.K.: H.M. Treasury, 2007).

6. See also NRC, Limiting the Magnitude; P. Watkiss, and T. Downing, "The social cost of carbon: Valuation estimates and their use in UK policy" (Integrated Assessment Journal 8[1]:85, 2008).

7. NRC (Hidden Costs of Energy: Unpriced Consequences of Energy Production and Use [Washington, D.C.: National Academies Press, 2009]) found that "depending on the [assumed] extent of future damages and the discount rate used for weighting future damages, the range of estimates of marginal global damages can vary by two orders of magnitude."


8. See NRC, Limiting the Magnitude and NRC, America's Energy Future.

9. Iterative risk management is sometimes used interchangeably with the term adaptive risk management. We chose to use "iterative," because in this report, "adaptive" is used in other contexts (e.g., in the context of adaptation to climate change impacts). Also, for the ecosystem management community, adaptive risk management is a term of art with a specific meaning that does not fully encompass the concepts being discussed here. See NRC, Informing Effective Decisions for further discussion and references on this topic.

10. IPCC, Climate Change 2007 WG2; World Bank, Managing Climate Risk: Integrating Adaptation into World Bank Group Operations (Washington, D.C.: World Bank Group, 2006, available at ENVIRONMENTFACILlTYGEFOPERATIONS/Resources/Publications-Presentations/GEFAdaptationAugOó.pdf, accessed March 17, 2011); United Nations Development Programme (UNDP), A Climate Risk Management Approach to Disaster Reduction and Adaption to Climate Change (Havana: UNDP and Harvard Medical School Center for Human Health and the Global Environment, 2002); Australian Greenhouse Office, Climate Change Impacts and Risk Management: A Guide for Business and Government (Canberra: Australian Greenhouse Office, 2006); UK Climate Change Risk Assessment (

11. NRC, Informing Decisions in a Changing Climate, Adapting to the Impacts, and Informing Effective Decisions; G. Yohe and R. Leichenko, "Adopting a risk-based approach," pp. 29-40 in Climate Change Adaptation in New York City: Building a Risk Management Response, New York City Panel on Climate Change 2010 Report (Annals of the New York Academy of Sciences 1196, 2010).

12. See NRC, Advancing the Science and Limiting the Magnitude.

13. e.g., H. Raiffa, Decision Analysis: Introductory Lectures on Choice Under Uncertainty (Reading, MA: Addison-Wesley, 1968); E. Crouch and R. Wilson, Risk/Benefit Analysis (Cambridge, MA: Ballinger, 1982); G. Suter, Ecological Risk Analysis (Boca Raton, FL: Lewis, 1993).

14. e.g., IPCC, Climate Change2007 WG2,Chapter 19; J. B. Smith, S. H. Schneider, M. Oppenheimer, G .W. Yohe, W. Hare, M. D. Mastrandrea, A. Patwardhan, I. Burton, J. Corfee-Morloti, C.H.D. Magadza, H-M. Fussel, A. B. Pittock, A. Rahman, A. Suarez, and J-P van Ypersele. "Assessing dangerous climate change through an update of the Intergovernmental Panel on Climate Change (IPCC) 'reasons for concern.'" (Proceedings of the National Academy of Sciences 106[11]:4133-4137, 2009).

15. NRC, America's Energy Future; NRC, Electricity from Renewable Resources: Status, Prospects, and Impediments (Washington D.C.: National Academies Press, 2010).

16. Reviews of several experiences with emissions trading can be found in T. Tietenberg, "The tradable permits approach to protecting the commons: What have we learned?," pp. 197-232 in The Drama of the Commons, ed. E. Ostrom, T. Dietz, N. Dolsak, P. Stern, S. Stonich, and E. Weber (Washington D.C.: National Academy Press, 2002); and T. Tietenberg, "The evolution of emissions trading," pp 42-58 in Better Living Through Economics, ed. J. J. Siegfried (Cambridge, MA.: Harvard University Press, 2010).

17. NRC, America's Energy Future.

18. NRC, Hidden Costs of Energy.

19. P. N. Leiby, Estimating the Energy Security Benefits of Reduced U.S. Oil Imports (Oak Ridge, TN: Oak Ridge National Laboratory, 2007).

20. L. Elbakidze and B. A. McCarl, Sequestration offsets versus direct emission reductions: Consideration of environmental co-effects (Ecological Economics 60[3]:564-571, 2007).

21. M. R Shammin and C. W. Bullard, "Impact of cap-and-trade policies for reducing greenhouse gas emissions on U.S. households" (Ecological Economics 68[8-9]:2432-2438, 2009).

22. See NRC, Advancing the Science and Adapting to the Impacts.

23. This difference is due primarily to the fact that adjusting standards generally requires a lengthy notice-and-comment administrative process and often entails litigation, whereas cap-and-trade systems can be designed to automatically adjust over time and keep costs within reasonable bounds.

24. For example multi-attribute utility analysis methods (R. L. Keeney and H. Raiffa, Decisions with Multiple Objectives. Second Edition (Cambridge, UK: Cambridge University Press, 1993).


1. Copenhagen Accord (; G-8 declaration (

2. e.g., see J. Hansen, M. Sato, P. Kharecha, D. Beerling, R. Berner, V. Masson-Delmotte, M. Pagani, M. Raymo, D. Royer, and J. Zachos, "Target atmospheric CO2: Where Should humanity aim?" (The Open Atmospheric Science Journal, 2008[2]:217-223, 2008).

3. e.g., NRC, Limiting the Magnitude and Advancing the Science.

4. Meinshausen et al., "Greenhouse-gas emission targets"; M. R. Allen, D. J. Frame, C. Huntingford, C. D. Jones, J. A. Lowe, M. Meinshausen, and N. Meinshausen, "Warming caused by cumulative carbon emissions towards the trillionth tonne" (Nature 458:1163-1166, 2009); Wissenschaftlicher Beirat der Bundesregierung Globale Umweltveränderungen (WBGU, German Advisory Council on Global Change), Solving the Climate Dilemma: The Budget Approach (Berlin: WBGU, 2009).

5. e.g., see J. E. Aldy and R. N. Stavins, Post-Kyoto International Climate Policy: Implementing Architectures for Agreement. (New York: Cambridge University Press, 2010); J. B. Wiener and R. B. Stewart, Reconstructing Climate Policy: Beyond Kyoto (Washington, D. C.: American Enterprise Institute, 2003).

6. Clarke et al., "International climate policy architectures."

7. B. C. Murray, A. J. Sommer, B. Depro, B. L. Sohngen, B. A. McCarl, D. Gillig, B. De Angelo, and K. Andrasko. 2005. Greenhouse Gas Mitigation Potential in US Forestry and Agriculture (Washington, D.C.: Environmental Protection Agency, 2005); IPCC, Climate Change 2007 WG1; NRC, Limiting the Magnitude; NRC, Advancing the Science.

8. A Renewable Portfolio Standard requires electric utilities and other retail electric providers to supply a specified minimum amount of customer load with electricity from eligible renewable energy sources, with the goal of stimulating market and technology development and making renewable energy economically competitive with conventional forms of electric power. Such standards are in place in 29 states and the District of Columbia. Some have proposed "no-carbon" standards, which would include nuclear power as well as renewables.

9. NRC, New Tools for Environmental Protection: Education, Information and Voluntary Measures (Washington, D.C.: National Academy Press, 2002).

10. See, e.g., C. Fischer and R. G. Newell, "Environmental and technology policies for climate mitigation" (Journal of Environmental Economics and Management 55(2):142-162, 2008); T. H. Tietenberg, Emissions Trading: Principles and Practice. (Washington, D.C.: Resources for the Future, 2006); NRC, Limiting the Magnitude.

11. Trades of this kind regularly occur within the European Union's Emissions Trading System. These trades require only the measurement of actual emissions, not the estimation of what emissions would have been absent the trade. On financial flows within the EU ETS, see Aldy and Stavins, Post-Kyoto.

12. EMF22: Clarke et al., "International climate policy architectures;" A. A. Fawcett, K. V. Calvin, F. C. De La Chesnaye, J. M. Reilly, and J. P. Weyant, "Overview of EMF 22 U.S. transition scenarios" (EnergyEconomics 31[Supplement 2]:S198-S211, 2009).

13. A concept within economic theory wherein the allocation of goods and services by a free market is not efficient.

14. See NRC, Limiting the Magnitude for detailed discussion.

15. Some examples discussed in M. A. Brown and S. Chandler, "Governing confusion: How statutes, fiscal policy, and regulations impede clean energy technologies" (Stanford Law and Policy Review 19[3]:472-509, 2008, available at, accessed March 1, 2011): Ten states have no statewide energy codes for residential construction or have codes that predate 1998; seven states do not have net metering for distributed power generation; 41 states have not decoupled electric utility profits from electricity sales; and all states ban private electric wires crossing public streets, which forces would-be power entrepreneurs to use their competitors' wires.

16. See M. P. Vandenbergh, P. C. Stern, G. T. Gardner, T. Dietz, and J. M. Gilligan, "Implementing the behavioral wedge: Designing and adopting effective carbon emissions reduction programs" (Environmental Law Review 40:1054710554, 2010); P. C. Stern, G. T Gardner, M. P Vandenbergh, T. Dietz, and J. M Gilligan, "Design principles for carbon emissions reduction programs" (Environmental Science and Technology 44[13]:4847-4848, 2010).


17. As compared to a comprehensive carbon price, a renewable portfolio standard does not provide incentives for efficiency in energy use, and its support of only selected technologies is unlikely to produce least-cost outcomes. Similarly, a cap-and-trade system covering only some sectors would minimize costs within but not across sectors. A recent study of twenty CO2 reduction policies (Resources for the Future and National Energy Policy Institute (RFF/NEPI), Toward a New National Energy Policy: Assessing the Options (Washington, D.C.: Resources for the Future, 2010, available at, accessed March 4, 2011) suggests that through 2030, some alternatives to a comprehensive pricing systems (such as a cap-and-trade policy excluding transportation) are reasonably cost-effective.

18. As of February 2011, several bills have been introduced in Congress to delay or block the EPA from moving ahead with implementation of any new rules for regulating CO2 emissions (e.g., see: T. Tracy, "Greenhouse-gas rules targeted by lawmakers" [Wall Street Journal, January 6, 2011]).

19. RFF/NEPI, Toward a New National Energy Policy.

20. See NRC, Advancing the Science, Chapters 4 and 6.

21. Tribal communities are listed as a distinct category because Native American communities that live on established reservations have unique vulnerabilities, given their limited relocation options.

22. See NRC, Adapting to the Impacts for additional details and discussion.

23. See NRC, Adapting to the Impacts for numerous examples of such policies.

24. See NRC, Adapting to the Impacts for additional examples of currently existing maladaptive policies and practices.

25. See NRC, Adapting to the Impacts and references therein.

26. See NRC, Understanding Risk, Public Participation, and Informing Decisions.

27. NRC, Verifying Greenhouse Gas Emissions.

28. See NRC, Public Participation, Informing Decisions, and Informing Effective Decisions.


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