5.2.2. Climatic Trends in This Century
Although regional differences are relatively high, most of Europe has experienced
increases in temperature of about 0.8°C on average in this century (Schoenwiese
et al., 1993; Brazdil et al., 1996; IPCC 1996, WG I, Chapter 3; Onate and Pou,
1996; Schuurmans, 1996). The increase has not been continuous throughout the
century; at most stations, an increase to about 1940 was observed, followed
by a leveling off or even a decrease until about 1970, and then a renewed warming
to the present period. These features are most pronounced in middle to high
latitudes. Some locations in southern Europe exhibit different trends-such as
in Greece and parts of eastern Europe, where some stations show a cooling trend
over much of the century (see Figure A-2 in Annex
A). During the most recent decade (1981-1990), warming over most of Europe
has been exceptionally great, with increases in yearly means of 0.25-0.5°C with
respect to the long-term average. The warming is most apparent in a belt extending
from Spain through central Europe into Russia. At some high-elevation sites
in the Alps, temperature increases have been even more marked, exceeding 1°C
in the 1980s (Auer and Boehm, 1994; Beniston and Rebetez, 1995). The 1980s have
exhibited annual temperature anomalies that are systematically in excess of
the long-term mean (see Figure A-7). Temperature rise
has been most marked during the winter period (see Figure
5-2); much evidence suggests that minimum temperature increases have been
far larger than changes in maximum temperatures (e.g., Beniston et al., 1994;
Brazdil et al., 1996). In other words, the diurnal temperature range is decreasing,
which is consistent with evidence from other regions of the world (e.g., Karl
et al., 1993). The geographical distribution of temperature trends emphasizes
greater warming (2°C per century) in the southWestern part of Europe (Iberian
Peninsula, south and central France) than in the British Isles or along the
Baltic coastline (1°C per century). The northern and central parts of European
Russia also have experienced greater warming than the European average-in some
places exceeding 3°C per century (see Figure A-2).
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| Figure 5-2: Annual winter (DJF) temperature anomaly over Europe
during the period 1900-96. |
Annual precipitation trends in this century are characterized essentially by
enhanced precipitation in the nothern half of Europe (i.e., north of the Alps
to northern Fennoscandia), with increases ranging from 10% to close to 50%.
The region stretching from the Mediterranean through central Europe into European
Russia and Ukraine, by contrast, has experienced decreases in precipitation
by as much as 20% in some areas (see Figure A-1). In
time-series analyses of precipitation averaged over the European region (see
Figure A-7), it is difficult to determine a meaningful
trend in precipitation, especially since the 1950s. The interannual variability
seems to have decreased in the latter part of the record: The amplitude of departures
in precipitation from long-term averages is far less than in the first half
of the century. This pattern does not necessarily mean that the amplitude of
interannual variability has decreased at the regional scale or at specific sites.
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