The Analogue Method

The analogue studies use as analogues of a high-C02 world wann periods taken from either paleoclimatological reconstruction of, for example, the Medieval Warm Epoch, the mid-Holocene, and the last interglacial (Eemian) or instrumental period. For the Arctic, our knowledge concerning the climates of the above periods (other than the instrumental) is not sufficient. Therefore, only the second approach is acceptable. The major advantage of scenarios based on the instnimcntal records, according to Palutikof (1986), is that it allows the construction of very detailed regional and seasonal scenarios constrained only by the density of the observing network. Scenarios of the Arctic climate (air temperature and precipitation) using this method have only been constructed by Przybylak (1995, 1996a, 2002a). One can also find some information about the climate change in the Arctic in a high-C02 world in papers analysing greater areas (Jäger and Kellogg (1983) for the southern fragment of the Arctic and Palutikof (1986) for the Canadian Arctic and for the southern part of Greenland). The major disadvantage of this method used for the Arctic and for other parts of the world is the fact that a warm-cold difference in the instnimcntal rccord for which a dense and accurate recording network is available is much smaller than even the most conservative estimates of C02-induced warming. Therefore, the scenarios presented below can only be treated as indicative of conditions in the early years of C02-induced warming, i.e. for the early decades of the 21s' century.

According to scenarios presented by Przybylak (1995, 1996a, 2002a) in a wanner world the greater part of the Arctic also shows warming. The pattern of this warming is very similar in winter, spring, and for the year as a whole. The largest increases of air temperature occur in the eastern part of the Arctic, especially over the Barents and Kara seas. The autumn air temperature exhibits the most peculiar behaviour. In this season less than half of the Arctic shows the wanning. The cooling should occur mostly in its western part (Greenland, Canadian Arctic and Alaska) and the Chukhotsk Peninsula, with the largest decreases over Alaska, Areally the greatest warming occurs in summer. Decreases of air temperature are found only over south and west coasts of Greenland, over Baffin Sea, and some small parts of the Russian Arctic, Winter shows the greatest extreme increases (or decreases) of air temperature in a warmer world (in both cases more than 1°C) while summer displays the smallest (mostly below 0.3°C), But the largest mean seasonal wanning in the Arctic (calculated from 27 stations) is found in spring (0.31°C), with a much lower mean in winter (0.17°C), and the lowest mean in autumn (0.01"C). A comparison of the mean seasonal and annual warming of the Arctic with the hemispheric wanning gives very interesting results. The intensity of the Arctic wanning is more than twice as great as for the Northern Hemisphere in spring and summer, while it is only a little greater in winter, and is much smaller in autumn. The mean annual wanning of the Arctic is 1.6 times greater.

The patterns of precipitation in the warmer world are more complex than those for air temperature (see Figure 1 in Przybylak 1995). This is connected with the greater spatial variability of precipitation. In all seasons except spring, the mean precipitation in the Arctic (computed from 27 stations) is lower in a warmer world. The increase occurs only in spring, which, as we remember, shows the most distinct warming. On the other hand, the largest decreases of the mean Arctic totals of precipitation are found in autumn, which is characterised by the lack of warming. However, the greater part of the Arctic shows a decrease of precipitation under warm-world conditions in winter, though these decreases are smaller than in autumn. In all seasons more than half of the Arctic shows decreases in precipitation. The winter precipitation is expected to increase only over the greater part of the Atlantic region of the Arctic and the Canadian Arctic. In spring the pattern is very similar; the main difference is the reduced area of precipitation increases. In summer, the increases and decreases of precipitation contain equal areas. The largest area of the precipitation increase includes Alaska, the Canadian Arctic, the eastern coast of Greenland, and the Greenland Sea. In autumn, in a wanner world there is a domination of the precipitation decrease, with the largest values over south-western Greenland and the Chukhotsk Peninsula (up to 40-50 mm). An increase is expected only over the Barents Sea and the adjoining islands. The annual precipitation shows a decrease over two areas: the largest one includes central and Russian Arctic and the smaller one is the southern part of Greenland with adjoining seas.

In conclusion, as pointed out by Przybylak (1995, 1996a, 2002a), a small warming and a decrease of precipitation connected with a rise in CO, in the first period of global wanning is expected in the Arctic. He found also that there is no direct relation between the behaviour of air temperature and precipitation. Increases and decreases of precipitation in the Arctic are expected to occur in the regions which show both warming and cooling.

This review reveals that both Arctic climatologists and climate modellers still have extensive work to do. On the one hand, our knowledge concerning the climatology of the majority of the meteorological elements in the Arctic, as well as some components of the Arctic climate system, is not sufficient to reliably check the validity of the numerical models. On the other hand, the existing climate models (both RCMs and especially GC'Ms) describe many Arctic processes inaccurately (e.g. cloud-radiative interactions, local surface-atmosphere interactions, sea ice distribution, stratiform clouds, and Arctic haze). As a consequence, the largest disagreement between climate model simulations of the present-day climate is in Polar regions. This also means that the reliability of the predictions of the Arctic climate in 2151 century using these models

(at present only GCMs) is still not satisfactory. The biases are especially high on regional and local scales. On the other hand, it was shown that both kinds of models are capable of correctly simulating the large-scale climate patterns. As follows from sub-chapter 11.1, the more recent versions of the RCMs, if they are to be used in the coming years to provide climate simulations, are capable of giving significantly better and more confident simulations than arc GCMs. To date, RCM simulations have been mostly aimed at evaluating models and processes rather than producing projections of future climate and, as such, they have been relatively short (10 years or less) (Houghton et al. 2001).

According to the latest GCMs results (transient models involving sulphate aerosol), the air temperature increase in the Arctic connected with the doubling of CO, varies between 2-5aC in winter and 0~1°C in summer. It is worth adding that the transient model experiment shows about 1.4-2.0 times lower warming in the Arctic than in the case of the equilibrium response. Most transient GCMs simulate an increase of precipitation in the Arctic with the doubling of COv The winter precipitation increase should be higher and more general than in summer. The inclusion of aerosol forcing additionally enlarges precipitation. According to the analogue method, at the beginning of the 21s' century a small wanning and a decrease of precipitation in the Arctic should occur. This means that the greatest difference between model and analogue scenarios becomes apparent in the case of precipitation in the Arctic.

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