Heat

Turn Down the Heat: Why a 4°C Warmer World Must Be Avoided
Box 3: Sub-Saharan Africa
Sub-Saharan Africa is a region of the world exposed to multiple stresses and has been identified as particularly vulnerable to the impacts of
climate change. It is an example of an environment where impacts across sectors may interact in complex ways with one another, producing
potentially cascading effects that are largely unpredictable.
For example, in a 4°C world, Sub-Saharan Africa is projected to experience temperatures that are well above currently experienced
extreme heat waves. In coastal areas, an additional problem will be sea-level rise, which is projected to displace populations, and particularly
in combination with severe storms, could cause freshwater resources to become contaminated with saltwater (Nicholls and Cazenave 2010).
Projected heat extremes and changes in the hydrological cycle would in turn affect ecosystems and agriculture.
Tropical and subtropical ecoregions in Sub-Saharan Africa are particularly vulnerable to ecosystem damage (Beaumont et al. 2011). For
example, with 4°C warming, of 5,197 African plant species studied, 25 percent–42 percent are projected to lose all suitable range by 2085
(Midgley and Thuiller 2011). Ecosystem damage would have the flow-on effect of reducing the ecosystem services available to human populations.
At present, food security is one of the most daunting challenges facing Sub-Saharan Africa. The economies of the region are highly
dependent on agriculture, with agriculture typically making up 20–40 percent of gross domestic product (Godfray et al. 2010a). Climate
change will likely cause reductions in available arable land (Brown, Hammill, and McLeman 2007). Because agriculture in Sub-Saharan Africa
is particularly sensitive to weather and climate variables (for example, 75 percent of Sub-Saharan African agriculture is rainfed), it is highly
vulnerable to fluctuations in precipitation (Brown, Hammel, and McLeman 2007) and has a low potential for adaptation (Kotir 2011). With 4°C
or more of warming, 35 percent of cropland is projected to become unsuitable for cultivation (Arnell 2009). In a 5°C world, much of the crop
and rangeland of Sub-Saharan Africa can be expected to experience major reductions in the growing season length (Thornton et al. 2011b).
For example, in the event of such warming, crop yields for maize production are projected to be reduced 13–23 percent across different
African regions (not taking into account the uncertain effect of CO 2
fertilization) (Thornton et al. 2011). Crop losses for beans are expected to
be substantially higher.
Human health in Sub-Saharan Africa will be affected by high temperatures and reduced availability of water, especially as a result of alterations
in patterns of disease transmission. Some areas in Sub-Saharan Africa may face a 50 percent increase in the probability for malaria
transmission (Béguin 2011) as a result of new species of mosquitoes becoming established (Peterson 2009). The impacts on agriculture
and ecosystems outlined above would further compound the direct impacts on human health by increasing the rates of undernutrition and
reduced incomes, ultimately producing negative repercussions for economic growth. These conditions are expected to increase the scale of
population displacement and the likelihood of conflict as resources become more scarce. Africa is also considered particularly vulnerable to
increasing threats affecting human security. Long-term shifts in the climate seem likely to catalyze conflict by creating or exacerbating food,
water and energy scarcities, triggering population movements, and placing larger groups of people in competition for more and more limited
resources. Increased climate variability, including the greater frequency of extreme weather events, will also complicate access to resources,
thereby exacerbating conditions that are conducive to promoting conflict (Brown, Hammer and McLeman 2007; Hendrix and Glaser 2007).
Like many other effects of climate change discussed in this report, instances of conflict could unfold “in a way that could roll back development
across many countries“(Brown, Hammer and McLeman 2007).
It is important to emphasize here that each of these impacts would undermine the ability of populations in Sub-Saharan Africa that are
often already facing poverty and precarious conditions to adapt to the challenges associated with impacts in other sectors. In this context,
the potential for climate change to act as a “threat multiplier,” potentially making such existing challenges as water scarcity and food insecurity
more complex and irresolvable, is cause for particular concern.
rising close to 35°C, or up to 9°C above the warmest July for the
past two decades. However, more research is required to better
understand the repercussions for agriculture in a 4°C world given
the uncertainty in both temperature and impact projections, as
well as the potential for adaptive responses and the possibility of
breeding high temperature crop varieties.
Similarly, social systems can be pushed beyond thresholds
that existing institutions could support, leading to system collapse
(Kates et al. 2012). The risk of crossing such thresholds
is likely to grow with pressures increasing as warming progresses
toward 4°C and combines with nonclimate related social,
ecological, economic, and population stresses. Barnett and Adger
(2003) point to the risks of sea-level rise in atoll countries pushing
controlled, adaptive migration to collapse, resulting in complete
abandonment. Similarly, stresses on human health—such as
heat waves, malnutrition, decreasing quality of drinking water
resulting from salt water intrusion, and more—could overburden
health-care systems to the point where adaptation to given
stresses is no longer possible. Immediate physical exposure of
facilities such as hospitals to extreme weather events, storm
surge, and sea-level rise may also contribute to this pressure
on health care systems.
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