The Impact of Climate Change on Natural Disasters - Reducing Disaster: Early Warning Systems for Climate Change - page 27

2.2.1 Extreme Climate and Weather Events

The Intergovernmental Panel on Climate Change (IPCC) released a special report
on extreme events and disasters in 2012 (IPCC SREX). In this report, IPCC assessed
the impact of climate change on extreme events and the consequences of these
events for the society and the environment as well as the implications on risk man-
agement (IPCC 2012a ). Expertise from climate change science and disaster risk
management was combined with scientists with knowledge in adaptation, vulnera-
bility and impact analysis. This 592-page document is a cross-disciplinary contribu-
tion from over 200 authors from 62 countries; it cites thousands of scientifi c studies
and has undergone three review rounds by experts and governments making sure
that the results are scientifi c sound and transparent (IPCC 2012a ).
This report concludes that climate extremes are a natural part of the climate sys-
tem, however “[a] changing climate leads to changes in the frequency, intensity,
spatial extent, duration, and timing of extreme weather and climate events, and can
result in unprecedented extreme weather and climate events” (IPCC 2012b ).
Extreme events can therefore be a consequence of a shift in the mean climate, the
variance, or the probability. A shift in the mean of, for example, temperature distri-
bution could increase extreme hot weather and reduce extreme cold weather.
Increased variability could lead to an increase in both extreme hot and cold weather
(see Fig. 2.5 ). Percentage wise the greatest change is recorded in the tails of the prob-
ability distribution function of climate variables (Trenberth 2011 ) where the climate
extremes are recorded.
Along this analysis of a shifting probability distribution, Hansen et al. ( 2012 )
illustrate the shift in global temperature anomaly distribution in the last 30 years by
analyzing past summer temperatures and expressing them in standard deviation
units. They illustrate how the anomaly distribution has broadened over the past
three decades relative to the 1951-1980 mean, making extreme hot summers more
frequent. They also found that the percentage of global land area that is experienc-
ing extreme hot summer outliers of +3

has increased substantially, by more than an
order of magnitude (Hansen et al. 2012 ).
Extreme events happen by defi nition seldom (IPCC 2012a ); identifying long-
term trends and making projections for the future are hence complicated. However,
certain past trends and future predictions can be established with varying confi -
dence (see Sects. 2.2.2 and 2.2.3 ).

σ

2.2.2 Past Trends

An increase in the number of hazardous events over the last few decades has been
noted by major insurance companies (e.g., Munich 2012 ), international disaster
databases (EM-DAT 2011 , UNISDR (see Fig. 2.6 )), as well as by the scientifi c com-
munity (IPCC 2012a ).