11.2.3 Climate Projections

11.2.3.1 Mean Temperature

The differences in near-surface temperature between the years 2080 to 2099 and the years 1980 to 1999 in the MMD-A1B projections, averaged over the West African (WAF), East African (EAF), South African (SAF) and Saharan (SAH) sub-regions, are provided in Table 11.1, with the temporal evolution displayed in Figure 11.1. The Mediterranean coast is discussed together with southern Europe in Section 11.3. In all four regions and in all seasons, the median temperature increase lies between 3°C and 4°C, roughly 1.5 times the global mean response. Half of the models project warming within about 0.5°C of these median values. The distributions estimated by Tebaldi et al. (2004a,b; see also Supplementary Material Table S11.2) have a very similar half-width, but reduce the likelihood of the extreme high limit as compared to the raw quartiles in Table 11.1. There is a strong correlation across these AOGCMs between the global mean temperature response and the response in Africa. The signal-to-noise ratio is very large for these 20-year mean temperatures and 10 years is typically adequate to obtain a clearly discernible signal, as defined in Section 11.1.2. Regionally averaged temperatures averaged over the period 1990 to 2009 are clearly discernible from the 1980 to 1999 averages.

Figure 11.1. Temperature anomalies with respect to 1901 to 1950 for four African 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.

The upper panels in Figure 11.2 show the geographical structure of the ensemble-mean projected warming for the A1B scenario in more detail. Smaller values of projected warming, near 3°C, are found in equatorial and coastal areas and larger values, above 4°C, in the western Sahara. The largest temperature responses in North Africa are projected to occur in JJA, while the largest responses in southern Africa occur in September, October and November (SON). But the seasonal structure in the temperature response over Africa is modest as compared to extratropical regions. The basic pattern of projected warming has been robust to changes in models since the TAR, as indicated by comparison with Hulme et al. (2001).

To date there is insufficient evidence from RCMs to modify the large-scale temperature projections from GCMs, although Tadross et al. (2005a) project changes in the A2 scenario for southern Africa that are lower than those in the forcing GCM and near the low end of the spread in the MMD models, likely due to a weaker drying tendency than in most of the global models.

Figure 11.2. Temperature and precipitation changes over Africa 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.