11.6.3 Climate Projections

11.6.3.1 Temperature

The warming as simulated by the MMD-A1B projections increases approximately linearly with time during this century, but the magnitude of the change and the inter-model range are greater over CAM and AMZ than over SSA (Figure 11.14). The annual mean warming under the A1B scenario between 1980 to 1999 and 2080 to 2099 varies in the CAM region from 1.8°C to 5.0°C, with half of the models within 2.6°C to 3.6°C and a median of 3.2°C. The corresponding numbers for AMZ are 1.8°C to 5.1°C, 2.6°C to 3.7°C and 3.3°C, and those for SSA 1.7°C to 3.9°C, 2.3°C to 3.1°C and 2.5°C (Table 11.1). The median warming is close to the global ensemble mean in SSA but about 30% above the global mean in the other two regions. As in the rest of the tropics, the signal-to-noise ratio is large for temperature, and it requires only 10 years for a 20-year mean temperature, growing at the rate of the median A1B response, to be clearly discernible above the models’ internal variability.

The simulated warming is generally largest in the most continental regions, such as inner Amazonia and northern Mexico (Figure 11.15). Seasonal variation in the regional area mean warming is relatively modest, except in CAM where there is a difference of 1°C in median values between DJF and MAM (Table 11.1). The warming in central Amazonia tends to be larger in JJA than in DJF, while the reverse is true over the Altiplano where, in other words, the seasonal cycle of temperature is projected to increase (Figure 11.15). Similar results were found by Boulanger et al. (2006), who studied the regional thermal response over South America by applying a statistical method based on neural networks and Bayesian statistics to find optimal weights for a linear combination of MMD models.

Figure 11.14. Temperature anomalies with respect to 1901 to 1950 for three Central and South American land regions for 1906 to 2005 (black line) and as simulated (red envelope) by MMD models incorporating known forcings; and as projected for 2001 to 2100 by MMD models for the A1B scenario (orange envelope). The bars at the end of the orange envelope represent the range of projected changes for 2091 to 2100 for the B1 scenario (blue), the A1B scenario (orange) and the A2 scenario (red). The black line is dashed where observations are present for less than 50% of the area in the decade concerned. More details on the construction of these figures are given in Box 11.1 and Section 11.1.2.

Figure 11.15. Temperature and precipitation changes over Central and South America from the MMD-A1B simulations. Top row: Annual mean, DJF and JJA temperature change between 1980 to 1999 and 2080 to 2099, averaged over 21 models. Middle row: same as top, but for fractional change in precipitation. Bottom row: number of models out of 21 that project increases in precipitation.

For the variation of seasonal warming between the individual models, see Table 11.1. As an alternative approach to estimating uncertainty in the magnitude of the warming, the 5th and 95th percentiles for temperature change at the end of the 21st century, assessed using the method of Tebaldi et al. (2004a), are typically within ±1°C of the median value in all three of these regions (Supplementary Material Table S11.2).