TURN DO WN THE H E AT: C L IM AT E E X T RE ME S , R EGION A L IMPA C TS, A N D TH E C A SE FOR R ESILIENCE
The following render agricultural productivity critically vulnerable to climate change: high dependence on precipitation combined with observed crop sensitivities to maximum temperatures during the growing season (Asseng et al. 2011; David B Lobell, Schlenker, and Costa-Roberts 2011a; Schlenker and Roberts 2009); varying and often uncertain responses to factors such as increasing CO2 concentration; and low adaptive capacities (Müller 2013). As a consequence, climate change is expected to affect agriculture by reducing the area suitable for agriculture, altering the growing season length, and reducing the yield potential (Kotir 2011; Thornton, Jones, Ericksen, and Challinor 2011a). The impacts of extreme events are as yet uncertain but are expected to be significant (Rötter, Carter, Olesen, and Porter 2011). Africa has already seen declines in per capita agricultural output in recent decades, especially for staple foods; the most important staple foods are cassava, rice, soybean, wheat, maize, pearl millet, and sorghum (Adesina 2010; Liu et al. 2008). Important factors include high levels of population growth, volatile weather, and climatic conditions that have seen droughts or flooding destroy or limit harvests. A number of other factors have also contributed, including use of low-productivity technologies and limited and costly access to modern inputs (Adesina 2010). Levels of malnutrition39 are high, partly as a result of this limited productivity and the high dependence on domestic production. The prevalence of malnutrition among children under five exceeds 21 percent (2011 data; World Bank 2013n) and one in three people in Sub-Saharan Africa is chronically hungry (Schlenker and Lobell 2010). The prevalence of undernutrition in Sub-Saharan Africa has decreased only slightly since the 1990s, from 32.8 percent (1990–92) to 26.8 percent (projections for 2010–12; Food and Agriculture Organization of the United Nations 2012a). An important factor remains: the yield potential of arable land in Sub-Saharan Africa is significantly higher than actually achieved (see Figure 3.13). Factors that limit yield differ across regions and crops. For example, nutrient availability is the limiting factor for maize in Western Africa, while water availability is an important co-limiting factor in East Africa (Mueller et al. 2012). The agricultural areas in Sub-Saharan Africa that have been identified as the most vulnerable to the exposure of changes in climatic conditions are the mixed semiarid systems in the Sahel, arid and semiarid rangeland in parts of eastern Africa, the systems in the Great Lakes region of eastern Africa, the coastal regions of eastern Africa, and many of the drier zones of southern Africa (Thornton et al. 2006). Faures and Santini (2008) state that relative poverty, which limits adaptive capacities of the local population and thus increases vulnerability, is generally highest in highland temperate, pastoral, and agro-pastoral areas. Those areas classified in the study as highland temperate areas include, for example, Lesotho and the highlands of Ethiopia and Angola; the pastoral zones include much of Namibia, Botswana, and the Horn of Africa; and the agro-pastoral zones include parts of the Sahel 38
Figure 3.13: Average “yield gap” (difference between potential and achieved yields) for maize, wheat, and rice for the year 2000
Source: Adapted from Mueller et al. (2012). Reprinted by permission from Macmillan Publishers Ltd: NATURE (Mueller et al., 2012, Closing yield gaps through nutrient and water management, Nature, 490), copyright (2012). Further permission required for reuse.
region and of Angola, Namibia, Botswana, Zimbabwe, Zambia, Kenya, and Somalia. Although (changes in) rainfall patterns are crucial for the Sahel region and a drying since the 1960s is well documented (Box 3.2), climate model projections of precipitation in this region diverge widely even in the sign of future change, not just for the generation of models at the time of IPCC’s AR4 but also for the latest CMIP5 generation of models used for AR5 (Roehrig et al. 2012). Sahel rainfall is closely linked to sea-surface temperatures in the 39 Defined as a physical condition that is caused by the interaction of an inadequate
diet and infection, and of which under-nutrition or insufficient food energy intake is one form (Liu et al. 2008; Roudier et al. 2011).