Heat

Focus: Changes in Extreme Temperatures
modeling studies on the increase of heat wave intensity over
the 21st century based on business-as-usual emission scenarios
(Meehl and Tebaldi 2004; Schär and et al. 2004; Stott et al. 2004) or
doubled CO 2
simulations (Barnett et al. 2005; Clark et al. 2006;
Zwiers and Kharin 1998). These results also corroborate recent
modeling studies indicating that the tropics are especially vulnerable
to unprecedented heat extremes in the next century (Beaumont
et al. 2011; Diffenbaugh and Scherer 2011).
The Impacts of More Frequent Heat
Waves
Given the humanitarian impacts of recent extreme heat waves,
the strong increase in the number of extreme heat waves in a
4°C world as reported here would pose enormous adaptation
challenges for societies. Prolonged heat waves are generally the
most destructive as mortality and morbidity rates are strongly
linked to heat wave duration, with excess deaths increasing each
additional hot day (Kalkstein and Smoyer 1993; Smoyer 1998; Tan
et al. 2006; Fouillet et al. 2006). Temperature conditions experienced
during these recent events would become the new norm in
a 4°C warmer world and a completely new class of heat waves,
with magnitudes never experienced before in the 20th century,
would occur regularly. Societies and ecosystems can be expected
to be especially vulnerable to the latter as they are not adapted to
extremes never experienced before. In particular, the agricultural
sector would be strongly impacted as extreme heat can cause severe
yield losses (Lobell et al. 2012) (see Section 6). Ecosystems in
tropical and sub-tropical regions would be particularly vulnerable
to climate change. The authors’ analysis show that the increase in
absolute temperatures relative to the past variability is largest in
these regions and thus the impacts on ecosystems would become
extreme here (see Section 6).
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