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

century. This corresponds to a sea level rise of 0.55 mm/year. All in all, the
observational evidence suggest that the sea level rise caused by thermal expansion
is about 1 mm/year for recent decades, in reasonable agreement with the predictions
of Atmosphere-Ocean General Circulation Models (AOCGMs) of 0.7 to 1.1 mm/year
over a similar period. The model simulations suggest that the ocean rise due to
thermal expansion over the 20 th century is 0.3 to 0.7 mm/year.
The available measurements only allow us to establish a mass balance for the rate of
change of a very small part of the more than 160 000 glaciers in the world. Thus the
input of water to the sea resulting from the retreat of glaciers must be estimated
based on a number of assumptions and approximations. The different approaches
that have been applied have lead to estimates of the contribution of glacier and ice
caps to sea level rise over the last century in the range of 0.2 to 0.4 mm/year.
The ice sheets of Greenland and the Antarctic contain enough water to raise sea
levels by 70 m, so fractional changes in these ice masses are of obvious importance.
The precipitation falling on the Arctic and Antarctic ice sheets is approximately
balanced by loss of ice due to melting and calving. The temperatures in the Antarctic
are so low that melting practically does not take place, while melting is of significant
importance in Greenland. The response time of ice discharge to climate change is
sufficiently long (100 to 10000 years) that it is likely that ice sheets now are still
adjusting to their past history. For the 21 st century it is expected by the IPCC that
surface mass balance changes will dominate the volume response of both ice sheets
(there is, however, considerable disagreement about this, as discussed below). Land
movements also influence sea levels; for this reason some places experience
decreasing sea level.
I.E. Climate Extremes
Changes in the mean value of climate variables such as temperature or precipitation
may also be associated with a change in their distribution, thus leading to either more
or less occurrence of extreme events; e.g. floods, droughts, very warm and very cold
spells.
Several studies have addressed the variability of global temperatures. The
observations give little evidence of an increase in inter-annual temperature variations
over the past few decades, but there is evidence suggesting that intra-annual
temperature variations have widely decreased. It has been found that much of the
warming in the mid- and high latitudes in the 20 th century has been during the cold
season, consistent with higher yearly minimum temperatures and a tendency towards
a narrower yearly temperature range. Some regional studies have also shown
decreasing diurnal temperature variations because of increasing night-temperatures.
The dramatic floods of central and Eastern Europe in August 2002, and the
subsequent severe drought and high temperatures of summer 2003 emphasize the
extreme in climatic variations.
As mentioned earlier, it may be expected that the increased release of latent heat
would lead to the occurrence of more intense precipitation events and analyses of
precipitation data show such a widespread tendency. Since the mid- and high latitude
land areas have experienced increasing precipitation during the last half of the 20 th
century the question arises if this has been associated with more extreme
precipitation events. The observations show such a tendency, although not uniform,
with a larger percentage of the precipitation falling into the upper five percentiles and
a 4% increase in the annual maximum five day precipitation in total.
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