Glaciers in Recession



One of the clearest signals of climate change comes from glaciers, which are in retreat on every continent of the globe. The changes in glaciers today can be compared directly with the ongoing warming of the atmosphere: the global glacier recession of the past 100 years corresponds to a global warming of about 0.66oC, and has added about 2­4 cm to the sea level.


In the European Alps, glaciers have shrunk by about 50 per cent in volume and 30­40 per cent in surface area since the middle of the 19th century, according to studies by Wilfred Haeberli of Zurich University, director of the UN World Glacier Monitoring Service. The recent emergence from melting ice of a deep­frozen stone­age man high in the Ötztal Alps suggests that the present retreat is the furthest in 5,000 years.


Ice is melting at a rate an order of magnitude faster than the average rate at the end of the last Ice Age, and appears to be accelerating. Since 1980, about 10­20 per cent of the remaining glacier volume of the Alps has since been lost. The situation is rapidly shooting beyond the range of natural variability known over the past 10,000 years.


The Gruben Glacier, for example, extending three kilometres down the side of the Fletschhorn in the Swiss Alps, has been retreating since the middle of the last century. The trend has accelerated since 1980. (The nearby Fee Glacier retreated 51 metres in one year.) Similarly the snowline, which had risen by 100 metres between the 1850s and 1980, has climbed another 100 metres since then. Saas Balen, a village below the Fletschhorn, is threatened by floods caused by the extra melting of snow and ice, and has twice been inundated by torrential runoff. Engineering work to protect the village in the future is costing around SFr 10 million.


A third to a half of the remaining glacier mass in mountain regions would disappear with a 4oC warming. In the European Alps, glaciers could be reduced to a few per cent of their present mass within decades.


One result of glacial melting over the coming decades will be extra runoff in rivers, increasing the risk of floods. Revegetation of the area left exposed following deglaciation is slow, leaving the ground vulnerable to erosion and rock slides for decades to centuries. Higher rainfall, as predicted for many regions, will also lead to greater runoff extremes, increasing the risk of flooding as well as the risk of landslides and mud slides. In May 1991, a landslide caused 16 million cubic metres of rock to plunge down a mountainside in the Matteral region of Switzerland, destroying a small village.


The pattern of glacial recession in the Alps is repeated in mountain ranges around the world from the poles to the tropics (see table).



Country or Region Extent of Retreat
Timescale
Caucasus, Pamirs, Tian Shan and Altai mountains of Central Asia

mountain glaciers shrunk by up to 4km past 200 years
Kazakhstan

glaciers reduced in extent by 14% 1955-1979
Central Asia

73% of 224 glaciers in retreat 1950s-1980s
Mount Kenya

glaciers in retreat since 1880s
Ecuadorian Andes and New Guinea

glaciers receding since the middle of the 19th century
Yanamarey glacier, Peru

shrinking fast ongoing
Cordillera do Mérida, Venezuela

snowline risen from 4,100m to 4,900m last 100 years
South Patagonia icefield

reduced by 500 km2 from 13,500km2 last 40 years
New Zealand

glaciers retreated by three km or more this century
Heard Island, Southern Ocean off Antarctica

general reduction of ice cover, for small glaciers by as much as 65% past 50 years
Western Greenland

marked retreat of ice this century
Northern Sweden and Spitsbergen

glaciers losing ground last 50 years



What will happen to the great icecaps of Greenland and Antarctica? These are by far the most massive ice sheets in the world. If the Western Antarctic Peninsula ice sheet melted, sea levels would rise by about six metres. The extent of these ice sheets has not changed greatly this century, nor would we expect them to as their response time to climatic changes is in the order of a thousand rather than a hundred years. However, there are signs that Antarctica's Wardie Ice Shelf is breaking up - it has shrunk by over 1,000 km2 in the last 25 years - and giant icebergs have broken away from the Larsen Ice Shelf, the largest break off occurring in February 1995.





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Copyright 1996, The World Wide Fund For Nature