World in Transition: Climate Change as a Security Risk - WBGU

56 5 Impacts of climate change on the biosphere and human society
Temperature deviation [°C]
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
1900 1920 1940 1960
Year
1980 2000 2020
rent trend would also be within this range. The narrow
bandwidth of the various developments concerning
temperature is due on the one hand to the
fact that emissions scenarios assume gradual changes
rather than drastic leaps in emissions, and on the
other to the inertia of the climate system, notably the
thermal inertia of the world’s oceans. Only very rapid
and radical changes in emissions of greenhouse gases
or aerosols, or unforeseeable events such as a major
volcanic eruption or meteorite impact would bring
about any marked deviation from the forecast outlined
above in the next 25 years. Gradual emissions
reductions over the coming decades, which would
most likely be implemented as part of an effective
climate protection policy, would not bring about any
notable slowdown in the global warming trend until
after 2030.
There will be considerable regional variation in
warming compared to the global trend, as indeed is
already the case. Figure 5.1-2 shows observed warming
trends for recent decades over land. While the
global temperature has risen by 0.6 ºC in the given
period, some regions are already registering a rise of
2 ºC or more. In this context, two effects merit particular
mention. First, the continents are warming
up faster than the global mean (in some regions up
to twice as fast, due to the moderating effect of the
oceans). Second, higher-latitude regions are warming
up especially quickly because shrinking snow and
ice cover leads to increased absorption of solar radiation.
As a result, people in two regions in particular
are starkly affected by the direct increase in mean
temperatures: the northern Polar regions ( Alaska,
Siberia), due to the particularly rapid rise in temperatures
and its impact on permafrost soils and infrastructure;
and the tropical climate zones, due to the
Figure 5.1-1
Global-mean temperature
development over land
and sea up to 2006 based
on the NASA data set,
shown as deviations from
1990 (annual data points;
the line drawn through the
points shows the course
of temperature dynamics
smoothed over 11 years).
2005 was the warmest year
since records began. The
grey area and the dotted
lines show the future
scenarios of the IPCC
(2001), which take 1990 as
the baseline year. Observed
warming is currently in the
upper reaches of the IPCC
scenarios.
Source: Rahmstorf et al.,
2007
fact that temperatures there are already high to start
with.
Heatwaves have special significance. The European
heatwave in the summer of 2003 cost the lives of
between 30,000 and 50,000 people and, according to
figures published by the Munich Re insurance group,
is the biggest natural disaster to have occurred in
central Europe in living memory (Münchener Rück,
2004). The example shows that heatwaves can have
devastating consequences even in temperate zones
and affluent countries, if society is ill-prepared to deal
with them. In Germany, 2003 saw the biggest losses
in terms of wheat yield since at least 1960 (Sterzel,
2004). This heatwave occurred suddenly and was well
above the long-term temperature trend (in Switzerland,
temperatures for June were around 3 ºC higher
than in the previous record year, 2002); it could not
have been anticipated, therefore, even taking global
warming trends into account. The physics underlying
this heatwave is not yet fully understood; various
attempts are currently being made to explain it. For
this reason, it is also impossible to predict where and
when in the future such extreme heatwaves may be
anticipated. Around the middle of the century, however,
it is expected that high summer temperatures
such as those experienced in 2003 will no longer represent
a heatwave, but will have become the norm
(Schär et al., 2004; Seneviratne et al., 2006).
In the longer term (in the second half of the 21st
century), temperature dynamics depend to a large
extent on which emissions scenario is applied. With
effective climate protection measures (stabilizing
the greenhouse gas concentration at below 450ppm
CO 2 eq), it is anticipated that global warming can be
restricted to a maximum of 2 ºC above pre-industrial
levels. In the absence of effective climate pro-