Results

2007ES000231-fig01
Figure 1
[10]  It is known that XX century was characterized by increased values (by 0.6-0.7oC) of the globally averaged near-surface air temperature. To be able to adequately predict the future climate changes, the model is required to adequately reproduce the climate changes occurred in the XX century. Figure 1 shows the temporal evolution of the surface temperature based on observation data [Jones et al., 1999], on data of five numerical experiments using the INM RAS model with XX-century observed changes in the concentrations of greenhouse gases and other external influences, as well as on data of 3 numerical experiments where all influences were fixed at the level of 1871. In addition to the mentioned general warming in the XX century, there were also an observed warming in the 1940-50s and some cooling in the 1960-70s. In all numerical experiments with actually observed influences in the XX century, the temperature increases by 0.7-0.9oC, which is close to or slightly higher than the observed warming value. In addition, these experiments yield a slight maximum of temperature in the 1940-50s and a slowdown in the warming in the 1960-70s. An analysis of the numerical calculations shows that the XX-century warming is mostly due to increased concentrations of greenhouse gases, which is partially compensated by the cooling caused by increased concentrations of sulfate aerosols. The slight maximum of temperature in the 1940-50s is caused by the enhanced level of solar radiation and by the absence of volcanic aerosols in these years, while the slowdown in the warming in the 1960-70s is connected [Meehl et al., 2004] with the decreased value of solar radiation and frequent volcanic eruptions.

[11]  The three experiments with constant-in-time influences fixed at the 1871 level show that there is no warming in the XX century (Figure 1). This means that the warming observed in the XX century appears to be the caused by not only the inner variability of the climate system. An analysis of the results of other models also shows that none of these models succeeded in obtaining the value of warming by 0.6-0.7oC during the century for fixed concentrations of greenhouse and other gases [Brocoli et al., 2003; Meehl et al., 2004].

2007ES000231-fig02
Figure 2
[12]  Figure 2 presents a prediction of variation in the globally averaged temperature in the XXI century derived by the INM RAS model. The temperature increase in the late XXI century as compared to 1981-2000 will constitute around 3.5oC for scenario A2. The value averaged over all models involved in this experiment is equal to 3.4oC, and the scattering between all models is in the range between 2.3oC and 3.9oC. The warming value in the INM RAS model for scenario A1B is some 2.6oC, and the model-averaged value is 2.7oC, with a scattering between all models from 1.9oC to more than 4oC. The warming value in the INM RAS model for scenario B1 is some 2oC, while the model-averaged value is 1.8oC, with a scattering between all models in the range between 1.0oC and 3.3oC. Thus, for all the scenarios, the warming value predicted by the INM RAS model is close to that averaged over all models. Even if the concentrations of all gases are kept unchanged at the level of 2000, the model predicts a temperature increase during the XXI century by almost a degree, which is connected with thermal inertia of the ocean.

[13]  The temperature increase in global warming is not the same for different geographical areas and seasons of the year. According to the results of the INM RAS model, the warming in December-February will be the strongest in the Arctic (constituting more than 10oC), where the ice in many regions will turn from multiyear to seasonal. The warming is significantly higher than the average value at moderate latitudes of Eurasia and North America, where the temperature increase reaches up to 5-7oC. The expected value of warming is some 3oC in the continental tropics and 1-3oC over most of the oceans. The lowest temperature increase is expected in the southern ocean. In June-August, the maximum warming (reaching up to 10oC) is concentrated in the vicinities of Antarctica. In summer, at moderate latitudes of Eurasia and North America, the expected value of warming is 2-4oC, which is smaller than the value of winter warming. Unlike winter, the summer temperature increase in the tropics is stronger than at moderate and high latitudes. These geographic features of global warming are inherent to the predictions calculated with the help of most models [Houghton et al., 2001].

[14]  The amount of precipitation at moderate and high latitudes will increase by 10-20% of the current value. The amount of precipitation in most of the subtropics will decrease, with the most considerable decrease being registered in the Mediterranean as well as in Central America and the Atlantic areas adjacent to it. In many near-equatorial areas, the amount of precipitation will slightly increase by global warming. These features of the redistribution of precipitation are also typical to the majority of modern models. In line with this, there will be a 10-20% increase in the river runoff and moisture content in soil at the most part of moderate and high latitudes and a decrease of the same value in the most part of subtropical areas. The most considerable decrease in the soil humidity will be registered in the Southern Europe, Near East, and Middle East. In near-equatorial areas, one may expect an increase in the soil moisture.

[15]  In the late winter, the model-calculated area of sea-ice cover in the Northern hemisphere in the XX century constitutes 12-13 million km2, which is close to the estimates from observational data. In the late XX century, the decrease in the area of sea-ice cover starts to exceed the value of the natural interannual variability. In the XXI century, the area of sea-ice cover decreases further. The data for the three scenarios under consideration differ from one another only slightly. The model-calculated area of sea-ice cover in the late XXI century will be 10, 9.5, and 9 million km2 for scenarios A2, A1B, and A2, respectively. In other words, the area of sea-ice cover in the late XXI century will decrease by 20-30% according to the numerical prediction. In the late summer, the change in the area of sea-ice cover is much more substantial. In the early XXI century, the model-calculated area of sea-ice cover in the Northern hemisphere will decrease by 25% as compared to the first half of the XX century, which is consistent with the existing estimates from observational data [Waple et al., 2004]. In the late XXI century, the area of sea-ice cover in September can constitute almost 20% of the area obtained for the XX century under scenario B1, almost 10% for scenario A1B, and almost completely vanishing for scenario A2. The majority of other models also yield significant changes in the area of sea-ice cover in the Northern hemisphere in the late summer, and in the late XXI century the Arctic ice melts downs completely or almost completely.

[16]  A key aspect of global warming is the sea-level rise. According to Houghton et al. [2001], the sea-level rise in the XX century constituted 10-15 cm, caused mainly by thermal expansion of ocean waters. The next important factor influencing on the sea-level change is the melting of mountain glaciers, which contributes to only 30-40% of the total sea-level rise in the XX century, according to the estimates of Bindoff and Billebrand [2007]. These estimates suggest that the melting of continental ices in Greenland and Antarctica has practically no contribution to the observed sea-level rise. Normally, mountain glaciers are of small area and taken to be subgrid-scale in climate models; therefore, the contribution of their melting to the rise of ocean level now is unlikely to be represented in climate models. However, the thermal expansion is a large-scale effect and can be adequately reproduced by models.

[17]  According to the results obtained by the INM RAS model, in the XX century the sea-level rise due to the thermal expansion was some 5 cm. All models involved in the intercomparison yield a value of the sea-level rise between 0 and 8 cm. The observation-based estimate of the contribution of the thermal expansion to the sea-level rise is 6-10 cm. Thus, the majority of models, including the INM RAS model, slightly underestimate the observed rise of ocean level due to thermal expansion.

2007ES000231-fig03
Figure 3
[18]  The value of the rise of the world-ocean level due to thermal expansion obtained by the INM RAS model for 2010 as compared to 2000 is 20 cm for scenario A2 (see Figure 3), while all other models yield a value in the range between 14 and 34 cm. For scenario A1B, the INM RAS yields a value of 17 cm, while all other models yield a value in the range between 12 and 35 cm. For scenario B1, the INM RAS yields a value of 13 cm, while all other models yield a value in the range between 9 and 27 cm. Thus, the estimates for the world-ocean level change by the INM RAS model are in the lower half of the scattering of this value over all models. In view of the fact that the near-surface warming in the model is close to the averaged value, it can be inferred that the INM RAS model warms up a slightly smaller layer of the ocean than the layer averaged over all models. For fixed concentrations of greenhouse gases in the XXII century, due to thermal inertia of the ocean, the ocean-level rise will be continued, reaching values of 48, 36, and 28 cm for 2200 calculated by the INM RAS model for scenarios A2, A1B, and B1, respectively, as compared to the early XX century. The results of numerical calculations carried out by the INM RAS model indicate that in the XXI and XXII centuries, the contribution of melting of the Greenland and Antarctic ices to the rise of the ocean-level rise remains small in comparison with the thermal expansion.

2007ES000231-fig04
Figure 4
[19]  Now, we analyze the climate changes in the territory of Russia. Let us consider not only the variation of values averaged over a long time period, but also extreme weather conditions. The warming value averaged over all the Earth is around 3.3oC for scenario A1B. On the territory of Russia, the winter warming exceeds the average value and constitutes from 4oC in the south to 6-8oC in central regions and 8-9oC in the north. The warming over the Arctic exceeds 10oC. In the warmest winter months, the warming is smaller than the average value and constitutes mainly 3-6oC except for some regions of central Siberia, where the warming value reaches up to 6-8oC. On the contrary, in the coldest winter months, the warming is higher than the average value and constitutes in the most part of Russia 8-12oC (Figure 4).

[20]  In summer, the warming in Russia is a maximum in the south, reaching there up to 5-6 oC, and a minimum on the Arctic coast, with a value of 3-4oC. In the warmest summer months, the temperature rise caused by global warming is somewhat stronger than on the average over all summer months, with a warming value in the south reaching 6-7oC. In the coldest summer months, the temperature rise is weaker than on the average. Thus, in global warming, the climate extremity with respect to temperature declines in winter and rises in summer. This occurs due to the fact that the extreme temperature situations emerge through different mechanisms.

2007ES000231-fig05
Figure 5
[21]  Figure 5 shows the variation of precipitation on the territory of Russia from 2101 to 2200 for scenario A1B in comparison with 1901 to 2000 for summer (May to September). In the northern half of this territory, there occurs a precipitation rise by a factor of 1.1-1.5. The decline in precipitation down to 0.7-0.9 of the average value in the course of the XX century is registered in south Russia and clearly expressed in southern Europe (around the Mediterranean). The relative variations in precipitation in the months with highest humidity for the Russian territory north of 55?N constitute a value between 1.1 and 1.3. In the south, where the amount of precipitation decreases on the average, this amount in the extreme rainy months in global warming shows no considerable changes. On the contrary, in the months of highest dryness, the amount of precipitation in the Russian south as well as in the most part of Central Asia and the Mediterranean decreases by a factor of 1.5-4. Thus, in dry regions the months of highest dryness are characterized by specifically enhanced dryness. In northern regions, the global warming makes the amount of precipitation in the months of highest dryness to increase by a factor of 1.3-1.7; i.e., droughts become less expressed.

[22]  Under global warming on the territory of Russia, there will occur also a noticeable growth in the vegetation period. The growth is expected to be the highest (up to 40-50 days per year) in 2001-2100 for scenario A1B in comparison with 1981-2000 in central regions of the European part of Russia. This is closely connected with the reduced number of frosty days per year. In Siberia as well as in the south of Russia, the growth in the vegetation period and the reduction of frosty days constitutes 20-30 days per year.

[23]  Let us consider also the extent of permafrost in soil. In 2081-2100 the permafrost boundary will move northeastward from the current position by almost 1000-1200 km for scenario B1 and 1000-1200 km in addition for scenario A2. In the latter case, the continuous permafrost areas will be present only in Taimyr and the Arctic coast of East Siberia, while sporadic permafrost areas will be found only in the Siberian polar region.

RJES

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