Assumptions about future trends

13.3.1 Climate

133.1.1 Climate-change scenarios

Even though climate-change scenarios can be generated by several methods (IPCC, 2001), the use of GCM outputs based on the Special Report on Emissions Scenarios (SRES: Nakicenovic and Swart, 2000) is the adopted method for the Fourth Assessment Report (AR4). Projections of average temperature and rainfall anomalies throughout the current century derived from a number of GCMs are available at the IPCC Data Distribution Centre (IPCC DDC, 2003; at a typical model resolution of 300 km, and for two different greenhouse-gas (GHG) emissions scenarios (A2 and B2). Additionally, Chapter 11 of the Working Group I Fourth Assessment Report (Christensen et al., 2007) presents regional projections for many parts of the world. Table 13.4 indicates ranges of temperature and precipitation changes for sub-regions of Latin America for several time-slices (2020, 2040, 2080), obtained from seven GCMs and the four main SRES emissions scenarios.

For 2020, temperature changes range from a warming of 0.4°C to 1.8°C, and for 2080, of 1.0°C to 7.5°C. The highest values of warming are projected to occur over tropical South America (referred to as Amazonia in Table 13.4). The case for precipitation changes is more complex, since regional climate projections show a much higher degree of uncertainty. For central and tropical South America, they range from a reduction of 20% to 40% to an increase of 5% to 10% for 2080. Uncertainty is even larger for southern South America in both winter and summer seasons, although the percentage change in precipitation is somewhat smaller than that for tropical Latin America. Analyses of these scenarios reveal larger differences in temperature and rainfall changes among models than among emissions scenarios

Table 13.4. Projected temperature (°C) and precipitation (%) changes for broad sub-regions of Central and South America based on Ruosteenoja et al. (2003). Ranges of values encompass estimates from seven GCMs and the four main SRES scenarios.

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