REPORTS - SPECIAL REPORTS

The Regional Impacts of Climate Change


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5.2.2. Climatic Trends in This Century

Although regional differences are relatively high, most of Europe has experienced increases in temperature of about 0.8C 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 0.25-0.5C 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 1C 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 (2C per century) in the southWestern part of Europe (Iberian Peninsula, south and central France) than in the British Isles or along the Baltic coastline (1C per century). The northern and central parts of European Russia also have experienced greater warming than the European average-in some places exceeding 3C per century (see Figure A-2).


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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