Climate Change and the European Water Dimension - Agri ...

The projected warming is not uniformly distributed: the land warms faster than the
sea and the strongest warming is expected at high latitudes.
The IPCC has been criticised by US scientists for paying too much attention to
unrealistically high CO2 emission scenarios (e.g. Hansen and Sato, 2001, Hansen et
al., 2001). These scientists also emphasise the relatively large contribution that non-
CO2 greenhouse gases and absorbing aerosols have given to global warming in
recent decades and propose to pay more attention to the benefits that may be
obtained by reduction of methane emissions and air pollution (ozone and absorbing
aerosols).
After the TAR, a detailed study of projected radiative forcings due to ozone changes
in the troposphere and the lower stratosphere in the 21 st century has been published
(Gauss et al., 2003). This study, based on a modified SRES emission scenario,
considered to be an upper limit for ozone precursor emissions, analysed the results
of 11 chemical transport models and used them as input for radiative forcing
calculations. The estimated radiative forcings from 2000 to 2100 due to the
increasing tropospheric ozone and the recovery of ozone in the stratosphere were in
the range from 0.40 to 0.78 W.m -2 with an average of 0.56 W.m -2 . The combined
forcings of all the well-mixed greenhouse gases in the same scenario is exactly 10
times as much.
Precipitation:
The predicted changes in precipitation in the 21 st century are pretty much in line with
the changes that have been found in the 20 th century. Globally water vapour and
precipitation are expected to increase, although not with a uniform distribution of the
precipitation (Figure I.6.). According to the modelling results, precipitation at high
latitudes will increase both summer and winter. Mean precipitation at subtropical
latitudes will decrease while precipitation in most tropical areas will increase. In spite
of the projected global increase in precipitation, decreases in soil moisture are
expected in mid-continental areas, because an increased potential evaporation is not
balanced by precipitation.
Sea level rise:
Projected changes in sea level over the 21 st century have been calculated using the
full set of SRES emission scenarios and seven AOGCMs. For each of the scenarios
the mean value of the model was calculated, this gave estimated sea level rises of
0.09 to 0.88 m over the period from 1990 to 2100. The mean value of this projected
rise corresponds to a rate of between two to four times the rate over the 20 th century.
The main cause of this rise is thermal expansion and melting of glaciers (0.11 to 0.43
m and 0.01 to 0.23 m, respectively). The thermal expansion is expected to accelerate
through the 21 st century. The contribution from Greenland (-0.02 to 0.09 m) and the
Antarctic (-0.17 to 0.02 m) are relatively small and could even be negative. Rising
sea levels will cause more frequent extreme high water levels; this tendency may be
further enhanced if the frequency or intensity of storms increases as a result of global
warming.
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