The P3 Scenario

The results of the P3 scenario are similar to those of the former scenario. Still, in some areas of the Arctic there are considerable differences between them. This scenario, according to the research done by Palutikof et al. (1984), is the most probable of all those presented so far. That is why the results have also been presented in a graphic form (Figures 7.2 and 7.5). In all seasons except spring, mean P in the Arctic along with global warming will be lower, especially in autumn. This overview of seasonal scenarios demonstrates, however, that P will decrease over the greatest area of the Arctic in winter (Figure 7.5). This discrepancy can be explained by the fact that the scale of those decreases in this season will be much smaller than in autumn. In winter a greater rise in P is expected mainly in the western part of ATLR (with the exception of southern Greenland), whereas it is much weaker in the north-western part of CANSRn and in the north of BAFR. Its greatest decreases will occur in the area surrounding southern Greenland, in the eastern part of ATLR, in SIBR, and in PACR. The spring scenario is very similar to the winter one, with the exception of the area of the Canadian Arctic, which will be characterised mostly by a rise of P during this season (Figure 7.5). In the summer period, although the Arctic will be drier on average, areas in which decreases and increases will occur will be similar in size. The greatest area where a rise in P will occur will encompass virtually the whole of the Canadian Arctic (with the exception of the areas surrounding stations Alert and Resolute A) and Alaska. Another area is situated in the western part of SIBR, whereas the third comprises mainly ATLSRw and part of the western area of ATLSRs (Figure 7.5). Still, the rises of P are slight and they rarely exceed 10 mm. Yet, the scale of the decreases is almost twice as big, reaching 20 mm in some areas. In autumn decreases in P in the Arctic will prevail, many of them exceeding 0.5a (Table 7.3). An increase in the humidity of the climate is mainly expected in Canadian Arctic (with the exception of its south-eastern part), and in some areas of the western and central part of ATLR.

The mean decrease of annual P in the Arctic along with global warming, calculated on the basis of 25 stations, will equal 8.3 mm. It should be drier in the eastern parts of ATLR, in SIBR, PACR, IARCR, and in the south of BAFR. The most significant decreases of P (> 0.5a) will occur in the eastern part of ATLR (excluding the areas surrounding Ostrov Dikson), in the western of PACR and on the south-western coast of Greenland. Their most significant rise will occur in the area spreading from Jan Mayen through Spitsbergen to Hopen, and in the south-western part of CANSRn (Figure 7.2).

Figure 7.5. Scenarios of changes in the seasonal totals of P (in mm) in the Arctic. Scenario P3. Areas with a decrease in P are hatched.

The above analysis indicates that the scenarios of changes in P along with global warming are complex. Areas where rises in P are expected are mingled with those where its decreases will probably occur. In each season a different distribution of changes in P is observable. Individual scenarios are also different from each other, although there are more areas for which at least four scenarios predict the same tendency of change. The greatest agreement was noted for annual sums (for as many as 18 stations), and the least for winter ones (only for 12 stations). Thus, in the case of these areas, there is a high probability that changes in P along with global warming will be as these scenarios demonstrate. The analysis of the data clearly indicates that in the forthcoming decades in the Arctic a decrease in P should occur. Such a vision is "forecast" by four out of the five scenarios (Table 7.3, Figures 7.2

and 7.5). These results are at variance with the results of the majority of climatic models, which predict a rise in P in the Arctic, along with global warming, connected with the doubling of C02 in the atmosphere (IPCC 1990). It appears that the results presented here are more credible, as they are based on data which have actually occurred in reality. Researchers who are involved in drafting climatic models usually associate the rise of P in the Arctic and other regions of the globe with increased evaporation during this time, and as a consequence, with the higher absolute humidity of the air (Washington & Meehl 1984). However, climatic models probably fail to reflect in an appropriate way the scale of the decrease of the advection of humid air masses from the south to the Arctic, which is induced by the weakening of the general atmospheric circulation along with the decrease of thermal gradient on the pole-equator line. Such a situation should occur immediately after the Arctic achieves a greater rise in T than other areas in the Northern Hemisphere. In fact, as this work has also pointed out (cf. Chapter 4 and sub-chapter 6.2), changes in the intensity of atmospheric circulation are a very important (and often the most important) factor shaping precipitation relations in those areas of the Arctic where its influence is the strongest (ATLR, PACR, and BAFR). It is therefore necessary to revise models in this respect.

The scenarios of future thermal conditions (sub-chapters 5.1.3 and 5.3.2) and precipitation conditions (sub-chapter 6.2.4) presented earlier for the Arctic as a whole, correspond to three variants of the construction of the scenarios based on the employment of analogues according to Pittock and Salinger (1982) (cf. sub-chapter 7.1). The comparison of those scenarios with the most credible scenarios from the P group (i.e. P2 and P3) makes it possible to confirm their general conformity.

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