S ub -S aharan A frica : F ood P roduction at R isk
world, African summer temperatures peak by 2050 at about 1.5°C above the 1951–80 baseline and remain at this level until the end of the century. In a 4°C world, warming continues to increase until the end of the century, with monthly summer temperatures over Sub-Saharan Africa reaching 5°C above the 1951–80 baseline by 2100. Geographically, this warming is rather uniformly distributed, although in-land regions in the subtropics warm the most (see Figure 3.3). In subtropical southern Africa, the difference in warming between RCP2.6 and RCP8.5 is especially large. This is likely because of a positive feedback with precipitation: the models project a large decrease in precipitation here (see Figure 3.6), limiting the effectiveness of evaporative cooling of the soil. The normalized warming (that is, the warming expressed in terms of the local year-to-year natural variability) shows a particularly strong trend in the tropics (Figure 3.3). The normalized warming is a useful diagnostic as it indicates how unusual the warming is compared to fluctuations experienced in the past. The monthly temperature distribution in tropical Africa shifts by more than six standard deviations under a high-emission scenario (RCP8.5), moving this region to a new climatic regime by the end of the 21st century. Under a low-emission scenario (RCP2.6), only localized regions in eastern tropical Africa will
witness substantial normalized warming up to about four standard deviations.
Projected Changes in Heat Extremes The frequency of austral summer months (DJF) hotter than 5-sigma, characterized by unprecedented temperatures (see the Chapter 2 on “Projected Temperature Changes”), increases over Sub-Saharan Africa under the high-emission scenario (Figure 3.4 and 3.5). By 2100, the multi-model mean of RCP8.5 projects that 75 percent of summer months would be hotter than 5-sigma (Figure 3.5) and substantially higher than the global average (see Chapter 2 on “Projected Changes in Heat Extremes”). The model uncertainty in the exact timing of the increase in frequency of extremely hot months is larger for Sub-Saharan Africa compared to the global mean uncertainty as averaging is performed over a smaller surface area. During the 2071–99 period, more than half (~60 percent) of Sub-Saharan African summer months are projected to be hotter than 5-sigma, with tropical West Africa in particular being highly impacted (~90 percent). Over this period, almost all summer months across Sub-Saharan Africa will be hotter than 3-sigma, with temperatures considered unusual or virtually absent in today’s
Figure 3.4: Multi-model mean of the percentage of austral summer months in the time period 2071–99
Temperatures greater than 3-sigma (top row) and 5-sigma (bottom row) for scenario RCP2.6 (left) and RCP8.5 (right) over Sub-Saharan Africa.
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