*, %, # - Trends statistically significant at the levels of 0.05; 0.01 and 0.001, respectively;a - Data from 1958;b - data from 1956;c - data for 1951-1997;" - data for 1951-1998;c - data from 1957; Other explanations as in Table 9.1

dian Arctic, in Alaska, the Chukchi Peninsula, and, primarily, in the western part of the Russian Arctic (Figure 9.7). In autumn, the greatest trends, which also exceeded 0.4°C/10 years, occurred only in the central part of CANR. Regions where positive and negative trends of T occurred in summer and in winter are similar to one another, except small areas in the Norwegian, Canadian, and Russian Arctic (Figure 9.7). Interestingly enough, the range of the values of the trends of Tdiffers considerably throughout the area of the Arctic. Both negative and positive trends are greater in winter than in summer. In these two seasons of the year, negative trends occur in southeastern part of the Canadian Arctic (they cover a larger area in winter), in BAFR, and in the western and eastern parts of ATLR. In summer, negative trends were also observed in the western part of SIBR. In both seasons of the year, the greatest warming (> 0.2°C/10 years) occurred in southwestern part of the Canadian Arctic and in PACR. In the latter region, the trends were statistically significant (Table 9.3).

Figure 9.7. The spatial distribution of the mean seasonal trends in T (°C/10 years) in the Arctic over the period 1951-2000. Key as in Figure 9.2.

As follows from Table 9.3, mean trends of seasonal and annual T, calculated for 34 Arctic stations over the period 1976-2000 are usually greater than analogous trends calculated for the period 1951-2000. They are also often statistically significant. Positive trends of T dominate in all seasons and in annual means. Negative trends in mean T for spring and for summer were observed at only two stations. As regards mean autumn and annual T, such a situation occurred at four stations, while in winter a cooling was observed over a considerable area of the Arctic. The cooling occurred in BAFR, CANR (except its southwestern part), PACR (except its northeastern part), and in isolated areas in the western part of the Russian Arctic. Trends of areally averaged T in this season were negative in almost all regions except ATLR (Table 9.3). A significant decrease was observed in BAFR (-0.85°C/10 years) and in PACR (-0.38°C/10 years). In the remaining seasons, the negative trend occurred only in BAFR in spring. The majority of statistically significant trends were noticed in this season (in three regions). According to mean annual T for the examined period, the greatest warming occurred in CANR (0.68°C/10 years) and in ATLR (0.55 °C/ 10 years), while the smallest was in BAFR (0.04°C/10 years). Mean TA (Arctic la) increased most in spring (0.80°C/10 years) and in autumn (0.60°C/ 10 years), while the lowest icnrease was in winter (0.11°C/10 years) (Table 9.3). Mean T for all seasons of the year (except winter) and annual T are statistically significant at the level of at least 0.01. It is worth emphasising that the trends of T are greater here than in whole Northern Hemisphere (Tnh) and in its northern part (Arctic 2a). This spatial distribution of the trends of T in the Northern Hemisphere has now become generally consistent with the expected changes in T connected with the increasing concentration of C02 and other trace gases. The greatest disparity concerns winter T that, according to the prognoses based on climatic models, should have warmed most. As has been mentioned earlier, winter thermal conditions in the Arctic are probably still shaped mostly by the atmospheric circulation that has been revealing a strong increase in zonal circulation (high values of NAO and AO indices) since the end of the 1980s.

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