The P3 Scenario

This scenario was constructed in a similar way to the P2 scenario, but instead of decades, twenty-year periods were used. That is why, in general terms, the scenarios should overlap to some degree. An analysis of Table 7.2 confirms this conclusion. Global warming will result in winter T values rising in the greater part of the Arctic, with the maximum reaching ca. 1.5°C in ATLSRe (Table 7.2, Figure 7.3). Still, they should decrease in the eastern part of CANR, in BAFR, in the part of ATLSRs which is adjacent to Greenland, and in the part of IARCSRa neighbouring the Canadian Arctic. The greatest decrease (ca. 1.5°C) is expected in BAFR. In spring the situation is generally similar to that in winter, except that the changes in T are less significant. Moreover, in CANR the decrease in T is limited exclusively to its easternmost part. It is worth noting, however, that the area of the greatest warming moves from ATLSRe in winter to the area of Spitsbergen in spring. In summer the greater part of the area will get warmer, although it will be far less significant than in winter and spring. A decrease in T will occur in this season only on the west, south, and south-east coasts of Greenland and in their immediate vicinity, and also in small parts of the Russian Arctic

Figure 7.2. Scenarios of changes of the mean annual T (in °C, left panels) and annual totals of P (in mm, right panels) in the Arctic. Scenarios A2 (upper panels) and P3 (lower panels). Areas with a decrease in T and P are hatched.

(Table 7.2, Figure 7.3). With global warming, the mean autumn TA does not indicate either a rise or a drop. The majority of ATLR and IARCR, and the whole of SIBR, will get slightly warmer, with the maximum being in Novaya Zemlya (by ca. 0.5°C). The remaining area of the Arctic will get cooler, (with the exception of a rather small area located in the central part of CANR (Figure 7.3)) with the maximum in PACR and in the western part of CANSRn (by ca. 0.5°C). The scenario for annual Tmost closely resembles T scenarios for winter and spring. The mean rise in TA along with global warming should be 0.16°C. The greater part of the Arctic will get warmer. Its maximum, reaching ca. 0.6°C, will occur in ATLSRn and ATLSRe. A decrease in T, not exceeding 0.5°C, will be limited to areas in the eastern part of CANR, the whole of BAFR, and small parts situated in the western part of ATLSRs and in IARCSRa (Figure 7.2).

Figure 7.3. Scenarios of changes of the mean seasonal 7" (in °C) in the Arctic. Scenario P3. Areas with a decrease in T are hatched.

Out of all five scenarios, the most credible are those whose construction involves long-term consecutive periods; these are the A2, P2, and P3

scenarios. Of those three, the best and most probable is the last scenario, based on twenty-year blocks of T. As Palutikof et al. (1984) note, the longer the sequence of consecutive years used, the more time is given for boundary conditions to adjust to the changes taking place. The term "boundary conditions" refers to the adjustment to changes in, for example, the extent of sea-ice or in SST. If we consider only a group of isolated years in the construction of a scenario, the above-mentioned processes cannot take place (because of lack of time), whereas the occurrence of the years that are extreme in terms of their thermal aspect may be caused, for example, only by anomalies occurring in the dynamics of the atmosphere, and may have no relation whatsoever to global warming induced by the rising concentration of and other trace gases.

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