Socioeconomic and demographic changes, and their effects on emissions, are shaping projected climate scenarios. However, given the long time period and feedback processes involved, along with the potential for extreme climate events, there is a high level of uncertainty regarding the precise reactions of the principal climate variables in each of the GHG emissions scenarios (A1B, B1, A2, A1F1, A1T and B2).1

For this reason,

temperature change projections (in degrees centigrade, comparing 2090-2099 to 1980- 1999), based on multiple climate models for different emissions scenarios, show increases of between 0.6℃ and slightly over 6℃ (figure 1.1), with effects varying from one region to another.

These projections, however, are subject to a considerable degree of uncertainty.

Climate projections for Latin America and the Caribbean (LAC) indicate that temperature increases will vary, according to the particular emissions scenario and country or region concerned. Based on the various climate models, it is projected that towards the end of the century (2090-2099), Latin America will experience an increase of between 1℃ and 4℃ under scenario B2 and between 2℃ and 6℃ under scenario A2 (IPCC, 2007a). In the specific case of scenario A1B, regional increases this century are projected to be between 1℃ and 4℃ compared to 1980-1999, with variances from one country to another (figure 1.2).

Projections for changes in precipitation patterns are extremely complex, involving a high degree of uncertainty and large heterogeneity . Thus, the predictions presented here, based on multiple general circulation

1 Scenario A1 assumes rapid demographic and economic growth, accompanied by the introduction of new and more efficient technologies; A1F1 is based on intensive use of fossil fuels; A1T presupposes that non-fossil-fuel energy will pre- dominate; A1B assumes a balanced use of all types of ener- gy sources; and A2 envisages lower economic growth, less globalization, and high and sustained demographic growth. Scenarios B1 and B2, for their part, include some mitigation of emissions through more efficient use of energy and im- proved technologies (B1), and more localized solutions (B2).

models (GCMs) and on the principal emissions scenarios, also show rainfall regimes varying from one part of the region to another (IPCC, 2007a). For Central America and tropical South America, predictions range from a 20% to 40% decrease in precipitation to a 5% to 10% increase by 2080. For the southern portion of South America, it is predicted that changes in precipitation will be plus or minus 12% in winter, and plus or minus 10% in summer.

Summer climate projections under scenario A1B show a reduction in precipitation of between 5% and 10% by the end of the century (2090-2099) in Central America as compared to 1980-1999 (figure 1.3), while for much of Mexico, southern Chile and the northeastern portion of the Bolivarian Republic of Venezuela, the decrease is projected to be between 10% and 20%. Projections call for a summer-time increase in the rainfall regime of between 5% and 10% in Ecuador, central and southern Colombia,

eastern Argentina and much of Peru. For the winter season, the

Warming of the earth’s surface Degrees centigrade

4.0 ºC

3.5 3.0

2.5 2.0

1.5 1.0

Note: Changes in surface temperatures for 2000-2099 compared to 1980-1999, according to SRES scenario A1B.

Source: IPCC: Climate Change 2007 Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007.

Figure 1.2 7