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Bold numbers denote the negative 10-year anomalies of air temperature

Bold numbers denote the negative 10-year anomalies of air temperature

Owing to the pronounced warming between 1996 and 2000, T in the 1990s was higher than normal in a significant area of the Arctic (Table 9.2, Figures 9.2 and 9.3). Anomalies calculated for the annual T for this decade reveal that the greatest warming (> 1.0°C) occurred in the northwestern and the northeastern parts of the Canadian Arctic and on the northern coast of Alaska (Figure 9.2). It was also significant in the Norwegian Arctic where T anomalies reached 1.0°C. In this decade, cooling only occurred in the southern part of BAFR and, most probably, in the southwestern part of the Greenland Region (GRER). Areally averaged annual T for the Arctic in this decade exceeded the norm by 0.6°C (Table 9.2). In the period 1951-2000, it was the warmest decade in the Arctic. Mean Tfor the climatic regions analysed in the present work revealed that it was the warmest in CANR, PACR (anomalies of 1.0°C), and in ATLR (0.6°C). A Twhich was slightly lower (-0.2°C) than the norm was characteristic ofBAFR. In all the analysed seasons during the 1990s, T in the Arctic was higher than in the previous forty years (Table 9.2, Figure 9.3). During this decade, spring and autumn T increased most (by 1.0°C and 0.7°C, respectively), while, as has been mentioned earlier, a significantly weaker warming occurred in winter (only by 0.2°C) (Table 9.2). Such a pattern of changes was observed in ATLR, PACR, and CANR; however, a slightly greater warming occurred in CANR in autumn. In comparison to the mean T for the period 1951-1990, the greatest warming in SIBR and BAFR occurred in summer (by 0.5°C) and autumn (by 0.3°C), respectively.

An analysis of the spatial distribution of seasonal anomalies of T in the decade 1991-2000 (Figure 9.3) fully confirms the conclusions obtained on the basis of areally averaged T. The picture shows that the warming was most common in spring and in autumn. In comparison to the anomalies calculated for the decade 1981-1990 (Figure 5.5 in the present work), the most significant changes in the 1990s occurred in autumn. These changes were particu-

Figure 9.2. The spatial distribution of the mean annual trends in T (°C/10 years, upper map) over the period 1951-2000 and the anomalies of mean annual 10-year (1991-2000) T, with the 1951-1990 mean (°C, lower map) in the Arctic.

Key: negative trends (anomalies) are hatched; dashed contours over the Arctic Ocean indicate that the data are extrapolated from the coastal stations.

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Figure 9.2. The spatial distribution of the mean annual trends in T (°C/10 years, upper map) over the period 1951-2000 and the anomalies of mean annual 10-year (1991-2000) T, with the 1951-1990 mean (°C, lower map) in the Arctic.

Key: negative trends (anomalies) are hatched; dashed contours over the Arctic Ocean indicate that the data are extrapolated from the coastal stations.

larly significant in the northwestern part of the Canadian Arctic and in the Norwegian Arctic. In the 1980s (negative) and the 1990s (positive) anomalies of T occurred in the greater part of the Arctic in all seasons. What is surprising is that, in the context of the greatest changes in winter T in the Arctic that were predicted by climatic models, the area covered by negative anomalies in this season showed no signs of becoming any smaller. Similar to the 1980s, these negative anomalies are present in BAFR and in the eastern part of CANR, while in the Norwegian Arctic the area of negative anomalies of winter T in the decade 1981-1990 moved further east (see Figure 5.5 in the present work). A new area with negative anomalies appeared in the northeastern part of the Russian Arctic (Figure 9.3). Such a spatial distribution of the anomalies of winter T is, to a large degree, consistent with the distribution of T anomalies that are caused by the influence of changes in atmospheric circulation. These changes may be determined by the NAO index (see Figure 12 in Przybylak 2000a). One should also notice the significance of the occurrence of major warming in summer, especially in the southwestern Canadian Arctic and in Alaska. By contrast, this warming was weak in the Central Arctic (usually

Figure 9.3. The spatial distribution of the anomalies of mean seasonal 10-year (1991-2000) T, with the 1951-1990 mean (°C) in the Arctic. Key as in Figure 9.2.

< 0.3°C). In the 1990s, the summer cooled slightly in the western part of the continental Russian Arctic and around southern Greenland (Figure 9.3). As has been mentioned earlier, this result differs significantly from those obtained by Chapman and Walsh (1993), and by Rigor et al. (2000) for the periods 1961-1990 and 1979-1997, respectively. They concluded that summer warming did not occur in the Arctic.

For all seasons except winter, and for particular years during the decade 1991-2000, changes in areally averaged T in the Arctic (Arctic la) correlate well with the changes in TNH (land + ocean) and with the changes in T (only land stations) in the zone stretching between 60-90°N (Arctic 2a) (Table 9.2). The greatest consistency of anomalies occurs in summer. As a result, during this season there was a much greater warming in Subarctic regions than in the real Arctic.

Since about the mid-1990s the rate of warming in the real Arctic became greater than the increasing rate of (Figure 9.4). Earlier, such a situation had occurred in the 1950s, the period ending the warming phase of the Arctic which had begun in the 1920s. In the years to come, the temperature in the Arctic may reach the level of the warming that occurred in the 1930s and 1940s - the greatest warming of the century.

In comparison both to the period 1951-1990 (Table 5.11, Figures 5.205.21) and to the period 1951-1995 (Table I, and Figures 5-8 in Przybylak 2000a), the inclusion of the data from the whole of the 1990s exerted a significant influence on the values of the trends of T (Table 9.3, Figures 9.2, 9.5, 9.6, and 9.7). From 1951 to 1990, T in the Arctic revealed negative trends for all seasons of the year and for annual means. These trends were statistically significant only in autumn. According to annual means, the greatest cooling of the Arctic occurred in BAFR (where trends were statistically significant), CANR, and ATLR. PACR was the only region that revealed a positive trend during this period. In the subsequent five years almost all the Arctic (except BAFR and the southwestern part of CANR) warmed slightly; however, taking this period into account did not lead to any major changes. Even though negative trends of annual T still dominated in BAFR, CANR, and ATLR, their values decreased (with the exception of BAFR). The values of trends increased significantly in PACR, and thus became statistically significant (Table I in Przybylak 2000a). Areally averaged Arctic T continued to reveal a negative trend (-0.04°C/10 years).

The inclusion of the 1990s in the calculations changed the trends of areally averaged T for all the Arctic and for particular regions (Figures 9.5 and 9.6), along with the spatial distribution of T in this area (Figures 9.2 and 9.7). In the period 1951-2000, the trend of areally averaged annual T in the Arctic (Arctic1a) is already positive (0.08°C/10 years) (Table 9.3, Figure 9.5). Positive trends also occurred in all seasons (Table 9.3, Figure 9.6). The high est increase in T was observed in spring (0.15°C/10 years), while the lowest occurred in winter and in summer (0.04°C/10 years). However, it should be emphasised that neither seasonal nor annual trends were statistically significant. These trends were significantly (usually 2-3 times) lower than in the area referred to as Arctic 2a. Except for spring and autumn, these trends are also lower than those that occurred in the last 50 years in the Northern Hemisphere, which were statistically significant in all individual seasons and for the year as a whole, usually at the level of 0.001 (Table 9.3).

1950 1960 1970 1980 1990 2000

Figure 9.4. Running 5-year mean annual anomalies of Tin the Arctic (Arctic la and Arctic 2a) and the Northern Hemisphere (NH) over the period 1951-2000.

Key: Arctic la - areally averaged T based on data from 37 Arctic stations (see Table 9.1 or Figure 9.1), Arctic 2a - areally averaged T for 60-90°N latitude band (after Jones et al. 1999, updated), NH - combined land+ocean areally averaged T for Northern Hemisphere (after Jones et al. 1999, updated).

1950 1960 1970 1980 1990 2000

Figure 9.4. Running 5-year mean annual anomalies of Tin the Arctic (Arctic la and Arctic 2a) and the Northern Hemisphere (NH) over the period 1951-2000.

Key: Arctic la - areally averaged T based on data from 37 Arctic stations (see Table 9.1 or Figure 9.1), Arctic 2a - areally averaged T for 60-90°N latitude band (after Jones et al. 1999, updated), NH - combined land+ocean areally averaged T for Northern Hemisphere (after Jones et al. 1999, updated).

In comparison to the period 1951-1995, the greatest changes in trend values were observed for areally averaged temperatures in ATLR, CANR, and BAFR. However, the period 1996-2000 did not significantly influence the trends of T in SIBR and PACR. In the period 1951-2000, the highest increase in annual T occurred in PACR (0.33°C/10 years) and was statistically significant. Positive trends were also observed in CANR and SIBR, though these were not statistically significant. ATLR did not reveal changes in T, and there was a cooling in BAFR. With the exception of these two regions and SIBR in autumn, mean seasonal trends of T in the remaining areas are positive. However, it was only in PACR that statistically significant trends occurred (excluding autumn) (Table 9.3).

The spatial distribution of mean annual (Figure 9.2) and seasonal (Figure 9.7) trends of T in the period 1951-2000 reveals pronounced changes, especially when compared to the spatial distribution from 1951 to 1990 shown in Figures 5.20 and 5.21, and, to a lesser degree, to the spatial distribution in the period 1951-1995 (Przybylak 2000a). Taking into consideration relations among the regions with positive and negative trends, it must be concluded that, in comparison to the period 1951-1990, the greatest reorganisation oc-

curred in transitional seasons of the year. In comparison to the period 19511995, this reorganisation was observed only in autumn. In the remaining seasons of the year, only slight changes occurred around the border between the areas with positive and negative trends of T.

curred in transitional seasons of the year. In comparison to the period 19511995, this reorganisation was observed only in autumn. In the remaining seasons of the year, only slight changes occurred around the border between the areas with positive and negative trends of T.

Figure 9.5. Year-to-year courses of mean annual anomalies of T and their trends in the climatic regions of the Arctic and for the Arctic as a whole over the period 1951-2000 (based on

Key: solid lines - year-to-year courses, heavy solid lines - running 5-year mean, and dashed

In the period 1951-2000, trends in annual T in the Arctic were positive throughout the research area, except for the southeastern part of CANR, the southern part of BAFR, and the southwestern and eastern parts of ATLR.

The greatest increases in Toccurred in the southwestern part of the Canadian Arctic and in Alaska, where a particularly high number of stations revealed statistically significant trends (see Table 9.3). Apart form Eureka station, trends greater than 0.2°C/10 years did not occur outside this region.

Figure 9.6. Year-to-year courses of mean seasonal anomalies of T and their trends in the Arctic over the period 1951-2000 (based on data from 37 stations).

Key: solid lines - year-to-year courses, heavy solid lines - running 5-year mean, and dashed lines - linear trends.

Figure 9.6. Year-to-year courses of mean seasonal anomalies of T and their trends in the Arctic over the period 1951-2000 (based on data from 37 stations).

Key: solid lines - year-to-year courses, heavy solid lines - running 5-year mean, and dashed lines - linear trends.

An analysis of the spatial distribution of the trends of T for particular seasons in the Arctic (Figure 9.7) confirmed the earlier assumption that the greatest warming occurred in spring and in autumn. It also follows from Figure 9.7 that warming was most common in the Arctic in these particular seasons of the year. In spring, negative trends were noticed only in the southeastern part of the Canadian Arctic, in the area around Greenland, and, most probably, in the southern part of GRER. In autumn, negative trends also occurred in this region, but they were quite limited and encompassed only the areas around southern Greenland. In this season, negative trends also occurred in the southern and eastern parts of ATLR and in the western part of SIBR. In spring, the highest increase in T(> 0.4°C/10 years) was observed in southwestern part of the Cana-

Table 9.3. Seasonal (DJF, MAM, JJA and SON) and annual (ANNUAL) air temperature trends (°C/10 years) in the Arctic

Station

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