The World in 2050_ Four Forces Shaping Civilization's Northern Future - Laurence C. Smith [155]
278 These outcomes are called SRES scenarios, of which three are shown here (i.e., each row is a different SRES scenario). There are many economic, social, and political choices contained within different SRES scenarios, but the differences are not important for our purposes here. SRES refers to the IPCC Special Report on Emissions Scenarios. They are grouped into four families (A1, A2, B1, and B2) exploring alternative development pathways, covering a wide range of demographic, economic, and technological driving forces and resultant greenhouse gas emissions. B1 describes a convergent, globalized world with a rapid transition toward a service and information economy. The A1 family assumes rapid economic growth, a global population that peaks around 2050, and rapidly advancing energy technology, with A1B assuming a balance between fossil and nonfossil energy. A2 describes a nonglobalized world with high population growth, slow economic development, and slow technological change. For more, see N. Nakicenovic, R. Swart, eds., Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge, UK: Cambridge University Press, 2000), 570 pp.
279 The three SRES scenarios shown, which I have renamed for clarity, are B1, A1B, and A2, respectively. There are a number of other scenarios but these three illustrate a representative cross-section from the IPCC AR4 Assessment.
280 P.217, R. Henson, The Rough Guide to Climate Change (London: Penguin Books Ltd., 2008).
281 These are discussed further in Chapter 9.
282 Projected temperature increases average about 50% higher over land than over oceans. The stubborn bull’s-eye marks where warm, north-flowing waters of the Meridional Overturning Current (MOC)—also known as the North Atlantic Deep Water Formation (NADW)—cool and sink. Weakened MOC overturning is expected to counter the climate warming effect locally in this area. There are other physical reasons why the warming effect is amplified in the high northern latitudes, including low evaporation rate, a thinner atmosphere, and reduced albedo (reflectivity) over land. But the most important reason by far is the disappearance of sea ice over the Arctic Ocean, changing it from a high-albedo surface that reflects incoming sunlight back out to space to an open ocean that absorbs it.
283 E.g., Figure 10.12, IPCC AR4, Chapter 10, p. 769. The models also concur pretty well in the Mediterranean region, southern South America, and the western United States, where precipitation is projected to decrease. They concur well around the equator, over the southern oceans around Antarctica, and throughout the northern high latitudes, where it is projected to increase. Except for Canada’s western prairies, precipitation is projected to rise significantly across the northern territories and oceans of all eight NORC countries.
284 Among other things the Clausius-Clapeyron relation, i.e., a warmer atmosphere holds more water vapor.
285 The 2050 projections are from P. C. D. Milly et al., “Global Pattern of Trends in Streamflow and Water Availability in a Changing Climate,” Nature 438 (2005): 347-350. That the projected northern runoff increases surpass all bounds of natural climate variability is shown by Hulme et al., “Relative Impacts of Human-Induced Climate Change and Natural Climate Variability,” Nature 397, no. 6721 (1999): 688-691. The twentieth-century river discharge increases appeared first and most strongly in Russia, B. J. Peterson et al., “Increasing River Discharge to the Arctic Ocean,” Science 298, no. 5601 (2003): 2171-2173; J. W. McClelland et al., “A Pan-Arctic Evaluation of Changes in River Discharge during the Latter Half of the Twentieth