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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