Global Outlook for Ice & Snow

cipitation, wind and cloudiness) influence the mass and energy balance at the glacier surface 7,8 . Air temperature plays a predominant role, as it is related to the radiation balance and turbulent heat exchange, and it determines whether precipitation falls as snow or rain. Over time periods of years and decades, changes in energy and mass balance cause changes in volume and thickness, which in turn affect the flow of ice through internal de- formation and basal sliding. This dynamic reaction eventually leads to changes in the length of the glacier – the advance or retreat of glacier tongues. In short, the glacier mass balance (the change in vertical thickness) is the direct signal of annual atmos- pheric conditions – with no delay – whereas the advance or retreat of glacier tongues (the change in horizontal length) is an indirect, delayed and filtered signal of climat-

In dry continental areas, on the other hand, such as northern Alaska, Arctic Canada, subarctic Russia, parts of the Andes near the Atacama Desert, and many cen- tral-Asian mountain chains (Figure 6B.3), the equilib- rium line is at a relatively high elevation with cold tem- peratures and short melting seasons. In such regions, glaciers far above the tree line can contain – or even consist entirely of – cold firn and ice well below melting temperature. These glaciers have a low mass turnover and are often surrounded by permafrost 3 . Glacier responses to climatic changes The response of a glacier to climatic change involves a complex chain of processes 5,6 . Changes in atmospheric conditions (such as solar radiation, air temperature, pre-

Figure 6B.2: Franz Josef Glacier, New Zealand. This temperate glacier receives several metres of precipitation a year and its tongue extends from almost 3 000 m above sea level down to 400 m above sea level, ending in the rainforest.

Figure 6B.3: Tsentralniy Tuyuksuyskiy Glacier, Kazhak Tien Shan in August 2006. This cold to partly temperate glacier extends from 4200 m above sea level to about 3400 m above sea level and is sur- rounded by continuous permafrost. Photo: V.N. Vinokhodov; data from the World Glacier Monitoring Service, Zurich, Switzerland

Photo: Michael Hambrey, SwissEduc (www.swisseduc.ch) and Glaciers online (www.glaciers-online.net); data from the World Glacier Monitoring Service, Zurich, Switzerland

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GLOBAL OUTLOOK FOR ICE AND SNOW

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