If projections of climate change for the year 2050 (UKMO-X5) are realized, a number of impacts on the cryosphere are likely. Projected warming of the climate would reduce the area and volume of the cryosphere. This reduction would have significant impacts on related ecosystems, people, and their livelihoods. There could be pronounced reductions in seasonal snow, permafrost, glaciers, and periglacial belts, with a corresponding shift in landscape processes. Pronounced alterations in glacier-melt runoff also are likely as the climate changes (IPCC 1996, WG II, Section 7.4).
Snow cover in the temperate regions ranges from a few meters to a few centimeters, but the snow often is close to its melting point; consequently, continental and alpine snow covers are very sensitive to climate. As warming occurs for many Asian mountains, there is a tendency for rainfall to occur at the expense of snowfall, although the extent of this shift depends on location. Less snow will accumulate at low elevations, although there may be more snow above the freezing level as a result of increased precipitation (IPCC 1996, WG II, Sections 7.3.1 and 7.4.1).
Glaciers are more sensitive to changes in temperature than to any other climatic element. For Asian glaciers, where precipitation occurs mainly during the summer monsoon season, temperature rise has a double effect. The first effect is an increase in the absorption of solar radiation caused by a lowering of the surface albedo, as snowfall is converted to rainfall. The second effect is an increase in energy exchange between the atmosphere and the glacier surface (IPCC 1996, WG II, Section 7.3.1). Both effects lead to an increase in glacial melting.
Empirical and energy-balance models indicate that a large fraction (about one-third to one-half) of the world's existing mountain glacier mass could disappear with anticipated warming over the next 100 years. By 2050, up to a quarter of mountain glacier mass may have melted. However, the largest alpine glaciers-such as those found in the Pamirs, the Tien Shan, and the Himalayas-are expected to continue to exist into the 22nd century. Other studies are based on calculations of ablation and equilibrium-line altitude, according to given climatic scenarios. Ablation would intensify in central Asia with climate warming because conditions there could become even more continental (IPCC 1996, WG II, Section 7.4.2).
The broad sensitivity of permafrost to past climate change is well documented in Siberia and China. There would be a poleward shift of permafrost zones, although deep-seated, ice-rich permafrost will be resistant to changes. Permafrost in northeast China is expected to disappear if temperature increases by 2°C or more. Over the Qing-Zang plateau, estimates of climate change impacts on permafrost range from complete disappearance for a temperature increase of 2°C to the raising of its elevation limit to 4,600 m for a warming of 3°C (IPCC 1996, WG II, Sections 7.3.3 and 7.4.3).
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