Temperature Variations After 1950

Detailed research into air temperature tendencies in the Arctic using data from 33 to 35 stations in the periods from 1951 to 1990 (Przybylak 1996a, 1997a, 2002a) and from 1951 to 1995 (Przybylak 2000a) revealed the predominance of negative trends, even though most of them were not statistically significant. Similar results have also been obtained by Chapman and Walsh (1993); Kahl et al. (1993a, b); Walsh (1995); Bom (1996); F0rland etal. 1997 and others.

The areally averaged seasonal and annual Arctic temperatures computed using data from 30 grid-boxes (after Jones 1994, updated) located in the study area are in good agreement with the above results obtained from the stations (see Przybylak 2000a). This data set, however, represents the Arctic without almost the entire region of Siberia. In addition, one should add that the quality of this type of data in its present state is significantly lower than the stations1 data used by Przybylak (2000a). In contrast to grid-box data, the temperature series from stations have no gaps. Taking these factors into account, identification of characteristics of long-term Arctic temperature variations should still be based on stations' data.

A comparison of temperatures calculated from stations and grid-boxes (Przybylak 2000a) indicates that the general patterns of seasonal and annual Arctic temperature variation are roughly similar. The greatest differences occur in winter and autumn. Correlation coefficients computed between these series entirely confirm these conclusions. The highest correlation was found for summer (r = 0.90) and spring (r = 0.82), and the lowest for winter (r = 0.55) and autumn (r = 0.66). For the annual values, the correlation coefficient is equal to 0.74. All these correlations are statistically significant at the level of 0.001.

Slight increases in air temperature in the Arctic have been prevailing in the recently observed "second phase of contemporary warming" (after 1975). However, they are up to four times smaller for the areally averaged Arctic air temperature than for the analogous series for the Northern Hemisphere (land + ocean). Such a situation occurred, for example, in the period 1976-1995 (Przybylak 2000a).

These results raise the following question: What are the causes of the lack of warming in the Arctic in the above period? According to Przybylak (1996a, 2000a, 2002a), this situation may result from:

(i) A delay in the reaction of the Arctic climatic system, which has considerable inertia because of large water masses, along with sea and land ice. One may liken the Arctic to a large refrigerator. To warm such a refrigerator, a significantly greater amount of energy must be supplied than would be necessary to warm a lower latitude region to the same degree. This means that the warming in the Polar regions connected with the increasing radiation forcing will occur later (not earlier as is commonly assumed) than in lower latitudes. This conclusion is consistent with results presented by Aleksandrov and Lubarski (1988). Analysing observational evidence, they found that in the phase of global wanning, the increase of air temperature in the Arctic was occurring later than in the lower latitudes. On the other hand, in the phase of global cooling, the opposite relation exists. It may be said that this conflicts with the warming in 1920-1940, which occurred earlier in the Arctic than in other parts of the world. This is correct, but the main reason for the latter wanning was a change in atmospheric circulation. As such, the reaction of climate to a change of forcing is immediate. The considerable inertia of an Arctic climate system should also significantly delay the start of positive feedback mechanisms (such as sea-ice - albedo - temperature feedback) which are responsible for a significant portion of Arctic greenhouse wanning.

(ii) The influence of natural factors (mainly a change in atmospheric circulation) which, while leading to a cooling of the Arctic, considerably reduces or completely removes the warming caused by the greenhouse effect. Przybylak (1996a, 2002a) shows that since the mid-1970s there have occurred significant increases in the frequency of the occurrence of the zonal macrotype of circulation (W) and decreases in the occurrence of the eastern macrotypc of circulation (E), according to the typology of Vangengeim-Girs (see e.g. Girs 1948, 1971, 1981; Vangengeim 1952; Barry and Perry 1973). The first macrotype gives negative temperature anomalies in the Arctic and the second gives positive ones. This means that the described circulation changes lead to the cooling of the Arctic. Other natural factors should also cause Arctic cooling, e.g. the statistically significant decrease of solar irradiance in the Arctic reported by Stanhill (1995) and the downward trend of solar activity observed since 1957 when the secular maximum occurred. Voskresenskiy et at. (1991) found decreasing Arctic temperatures in the periods of lower solar activity.

(iii) The influence of a rising concentration of anthropogenic sulphate aerosols. Santer et al. (1995) found that the anti-greenhouse effect made by sulphate aerosols since pre-industrial times is greater in most of the Arctic than the greenhouse effect connected with the rise of CO, during the same period.

(iv) The combined effect of these factors.

The above situation rapidly changed due to the pronounced warming of the Arctic between 1996 and 2000. Przybylak (2002a), using data from 46 stations (37 from the Arctic and 9 from the Subarctic), reported that the greatest wanning occurred in the Canadian Arctic and in Alaska, where 5-year anomalies fluctuated most often from 1-2°C above the 1951-1990 mean. Significant wanning also occuned in the Norwegian Arctic. The warming was clearly weakest in the Russian Arctic and on the western coast of Greenland. For the majority of the analysed stations, the pentad 1996-2000 has been the warmest since 1951. This is true of all stations in the Canadian Arctic and most of the stations in Pacific region (PACR). In the remaining area of the Arctic, the warmest pentad was usually that from the 1950s.

Table 10.2. Anomalies of mean seasonal and annual air temperatures from the decade 19912000 (in °C) in the Arctic referred to the mean 1951-1990

Area

DJF

MAM

JJA

SON

ANNUAL

Atlantic region

0.6

1.4

-0.1

0.5

0.6

Siberian region

-0.1

0.3

0.5

0.2

0.2

Pacific region

0.2

1.7

0.9

0.9

1.0

Canadian region

0.2

1.3

0.8

1.4

1.0

Baffin Bay region

-1.2

-0.4

0.1

0.3

-0.2

Arctic 1

0.2

1.0

0.4

0.7

0.6

Arctic 2

0.7

1.0

0.4

0.6

0.7

NH (land+ocean)

0.5

0.4

0.3

0.3

0.4

Bold numbers denote the negative 10-year anomalies of air temperature. Arctic 1 - areally averaged temperature based on data from 37 Arctic stations, Arctic 2 - areally averaged temperature for 60-90°N latitude band (after Jones el at. 1999, updated), NH (land + ocean) areally averaged temperature for Northern Hemisphere (after Jones et at. 1999, updated)

Bold numbers denote the negative 10-year anomalies of air temperature. Arctic 1 - areally averaged temperature based on data from 37 Arctic stations, Arctic 2 - areally averaged temperature for 60-90°N latitude band (after Jones el at. 1999, updated), NH (land + ocean) areally averaged temperature for Northern Hemisphere (after Jones et at. 1999, updated)

Air temperature in the 1990s was higher than normal in a significant area of the Arctic (Table 10.2, Figures 10.16 and 10.17). Anomalies calculated for the annual air temperature for this dccade reveal that the greatest warming (> 1.0°C) occuncd in the northwestern and the northeastern parts of the Canadian Arctic and on the northern coast of Alaska (Figure 10,16). ft was also significant in the Norwegian Arctic where air temperature anomalies reached 1.0°C. In this decade, cooling only occurred in the southern part of the Baffin Bay region (BAFR) and, most probably, in the southwestern part of the Greenland region (GRER). Areally averaged annual air temperature for the Arctic in this decade exceeded the nonn by 0.6°C (Table 10.2). In the period 1951-2000, it was the wannest dccade in the Arctic. Mean air temperatures for the climatic regions analysed in the present work revealed that they were warmest in the Canadian region (CANR), PACR (anomalies of

Figure 10.16. The spatial distribution of the mean annual trends in air temperature (°C/!0 years, upper map) over the period 1951 -2000 and the anomalies of mean annual 10-year (19912000) air temperature, 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.

Figure 10.16. The spatial distribution of the mean annual trends in air temperature (°C/!0 years, upper map) over the period 1951 -2000 and the anomalies of mean annual 10-year (19912000) air temperature, 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.

l.0°C), and in Atlantic region (ATLR. 0.6°C). An air temperature which was slightly lower (-0.2°C) than the norm was characteristic of BAFR. In all the analysed seasons during the 1990s, air temperature in the Arctic was higher than in the previous forty years (Table 10.2, Figure 10,17). During this decade, spring and autumn air temperature 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 10.2). Such a pattern of changes was observed in ATLR, PACR, and CANR; however, a slightly greater warming occurrcd in CANR in autumn. In comparison to the mean air temperature for the period 1951-1990. the greatest warming in the Siberian region (SIBR) and in BAFR occurrcd in summer (by 0.5°C) and in autumn (by 0.3°C), respectively.

Figure 10.17. The spatial distribution of the anomalies of mean seasonal 10-year (1991-2000) air temperature, with the 1951-1990 mean (°C) in the Arctic. Key as in Figure 10.16.

An analysis of the spatial distribution of seasonal anomalies of air temperature in (he decade 1991-2000 (Figure 10.17) fully confirms the conclusions obtained on the basis of areally averaged air temperature. 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 (see Figure 11 in Przybylak 1996a or Figure 5.5 in Przybylak 2002a), the most significant changes in the 1990s occurred in autumn. These changes were particularly significant in the northwestern part of the Canadian Arctic and in the Norwegian Arctic. In the 1980s (negative) and the 1990s (positive) anomalies of air temperature occurred in the greater pail of the Arctic in all seasons. What is surprising is that, in ¡he context of the greatest changes in winter air temperature 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 air temperature in the decade 1981 1990 moved further east (see Figure 5.5 in Przybylak 2002a). A new area with negative anomalies appeared in the northeastern part of the Russian Arctic (Figure 10.17). Such a spatial distribution of the anomalies of winter air temperature is, to a large degree, consistent with the distribution of air temperature 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 wanning in summer, especially in the southwestern Canadian Arctic and in Alaska. By contrast, this warming was weak in the central Arctic (usually < 0.3°C). In the 1990s, the summer cooled slightly in the western part of the continental Russian Arctic and around southern Greenland (Figure 10.17). 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 al! seasons except winter, and for particular years during the decade 1991-2000, changes in areally averaged air temperature in the Arctic (Arctic 1) correlate well with the changes in Northen Hemisphere air temperature (land + ocean) and with the changes in air temperature (only land stations) in the zone stretching between 60^90°N (Arctic 2) (Table 10.2). The greatest consistency of anomalies occurs in summer. As a result, during this season there was a much greater warning 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 Northen Hemisphere air temperature (Figure 10.18). 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 occuned in the 1930s and 1940s - the greatest wanning of the 20,h century.

Years

Figure 10.18. Running 5-year mean annual anomalies of air temperature in the Arctic (Arctic I and Arctic 2) and the Northern Hemisphere (N!f) over the period 1951-2000. Key: Arctic 1 areally averaged air temperature based on data from 37 Arctic stations (see Table 9.1 or Figure 9.1 in Przybylak 2002a), Arctic 2 - areally averaged air temperature for 60 90°N latitude band (after Jones et at. 1999, updated), NH - combined land+ocean areally averaged air temperature for Northern Hemisphere (after Jones et at. 1999, updated).

Years

Figure 10.18. Running 5-year mean annual anomalies of air temperature in the Arctic (Arctic I and Arctic 2) and the Northern Hemisphere (N!f) over the period 1951-2000. Key: Arctic 1 areally averaged air temperature based on data from 37 Arctic stations (see Table 9.1 or Figure 9.1 in Przybylak 2002a), Arctic 2 - areally averaged air temperature for 60 90°N latitude band (after Jones et at. 1999, updated), NH - combined land+ocean areally averaged air temperature for Northern Hemisphere (after Jones et at. 1999, updated).

In comparison both with the period 1951-1990 (Table 5.11, Figures 5.205.21 in Przybylak 2002a) and with 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 air temperature (Figures 10.16, 10.19, 10.20, and 10.21). From 1951 to 1990, air temperature 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 southwest-em part of CANR) wanned slightly; however, taking this period into account did not lead to any major changes. Even though negative trends of annual air temperature 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 air temperature 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 air temperature for all the Arctic and for particular regions (Figures 10.19 and 10.20), along with the spatial distribution of air temperature in this area (Figures 10.16 and 10.21). In the period 1951-2000, the trend of areally averaged annual air temperature in the Arctic (Arctic 1) is already positive (0.08°C/10 years) (Figure 10.19). Positive trends also occurred in all seasons (Figure 10.20). The highest increase in air temperature 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 2. 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 ihe year as a whole, usually at the level of 0.001 (Table 10.2).

Siberian region

Baffin Bay region

-3 1950

1960 1970 19B0 1990 2000

1960 1970 1980 1990 2000

-3 1950

Siberian region

1960 1970 19B0 1990 2000

Baffin Bay region

1960 1970 1980 1990 2000

Pacific region ,

7 ^y

r 1 f '

y

1 V

t950 1960 1970 1960 1990

t950 1960 1970 1960 1990

Arctic

1950 1960 1970 1980 1990 2000

Figure 10.19. Year-to-year courses of mean annual anomalies of air temperature and their trends in the climatic regions of the Arctic and for the Arctic as a whole 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, dashed lines - linear trends.

1960 1960 1970 1980 1990 2000

1950 1960 1970 1960 1990 2000

1960 1960 1970 1980 1990 2000

Figure 10.20. Year-to-year courses of mean seasonal anomalies of air temperature and their trends in the Arctic over the period 1951-2000 (based on data from 37 stations). Key as in Figure 10.19.

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 air temperature in S1BR and PACR. In the period 1951-2000, the highest increase in annual air temperature 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 air temperature, and there was a cooling in BAFR. With the exception of these two regions and SIBR in autumn, mean seasonal trends of air temperature in the remaining areas are positive. However, it was only in PACR that statistically significant trends occurred (excluding autumn).

In the period 1951-2000, trends in annual air temperature in the Arctic were positive throughout the research area, except for the southeastern part of CANR, the southern part of BAFR, and ihc southwestern and eastern parts of ATLR. The greatest increases in air temperature occurred 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 in Przybylak 2002a). Apart from Eureka station, trends greater than 0.2°C/10 years did not occur outside this region.

Figure 10,21. The spatial distribution of the mean seasonal trends in air temperature (°C/10 years) in the Arctic over the period 1951-2000 Key as in Figure 10.16.

An analysis of the spatial distribution of the trends of air temperature for particular seasons in the Arctic (Figure 10.21) confirmed the earlier assumption that the greatest warming occurred in spring and in autumn. It also follows from Figure 10.21 that warming was most common in the Arctic in these particular seasons. 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 SI13R. In spring, the highest increase in air temperature (> 0.4°C/I0 years) was observed in the southwestern part of the Canadian Arctic, in Alaska, the Chukchi Peninsula, and, primarily, in the western part of the Russian Arctic (Figure 10.21). 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 air temperature occurred in summer and in winter are similar to one another, except for small areas in the Norwegian, Canadian, and Russian Arctic (Figure 10.21). Interestingly enough, the range of values of the trends of air temperature differs considerably throughout the area of the Arctic. Both negative and positive trends are greater in winter than in summer. In these two seasons, negative trends occur in southeastern part of the Canadian Arctic (they covcr 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 SI BR. In both seasons, the greatest warming (> 0.2°C/10 years) occurrcd in the southwestern part of the Canadian Arctic and in PACR. In the latter region, the trends were statistically significant (Table 10.2).

Mean trends of seasonal and annual air temperature, calculated for 34 Arctic stations over the period 1976-2000, arc usually greater than analogous trends calculated for the period 1951-2000 (see Table 9.3 in Przybylak 2002a). They are also often statistically significant. Positive trends of air temperature dominate in all seasons and in annual means. Negative trends in mean air temperature for spring and summer were observed at only two stations. As regards mean autumn and annual air temperature, such a situation occurred at four stations, while in winter a cooling was observed over a considerable area of the Arctic. The cooling occurrcd 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 air temperature in this season were negative in almost all regions except ATLR. 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 air temperature 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 lowest was in BAFR (0.04°C/10 years). Mean Arctic air temperature (Arctic 1) increased most in spring (0.80°C/I0 years) and in autumn (0.60°C/10 years), while the lowest increase was in winter (0.11°C/10 years). Mean air temperature for all seasons (except winter) and annual air temperature are statistically significant at the level of at least 0.01. It is worth emphasising that the trends of air temperature are greater here than in whole Northern Hemisphere (NH) and in its northern part (Arctic 2). This spatial distribution of the trends of air temperature in the Northern Hemisphere has now become generally consistent with the expected changes in air temperature connected with the increasing concentration of CO, and other trace gases. The greatest disparity concerns winter air temperature that, according to the prognoses based on climatic models, should have wanned 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 zona!

circulation (high values of the NAO and the Arctic Oscillation (AO) indices have been observed since the end of the 1980s).

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