27/8/09

Earth enters the big thaw


BBC NEWS.Tuesday, 7 March, 2000, 14:54 GMT


By environment correspondent Alex Kirby Around the world, ice sheets and glaciers are melting at a rate unprecedented since record-keeping began. The Worldwatch Institute, based in Washington DC, has compiled reports from across the globe, which show that the melting accelerated during the 1990s - the warmest decade on record. The Institute says glaciers and other ice features are especially sensitive to temperature shifts, and that "scientists suspect the enhanced melting is among the first observable signs of human-induced global warming". Warming warning Many scientists believe the Earth is gradually warming up because of the release of heat-trapping gases into the atmosphere from human activity. But other researchers dispute this.



They point to inconsistencies in temperature records over the last century, and in particular the data measured from space and by high-altitude balloons which show no recent warming trend at all. Some of the examples of thinning ice in the Worldwatch report include:
- Arctic ocean sea ice: shrunk by 6% since 1978, with 14% loss of thicker, year-round ice. Thinned by 40% in under 30 years
- Greenland ice sheet: has thinned by more than a metre a year on its southern and eastern edges since 1993
Antarctic sea ice: ice to the west of the Antarctic peninsula shrank by about 20% between 1973 and 1993 - the decline continues
- Tien Shan mountains, central Asia: 22% of glacial ice volume has disappeared in the last 40 years
- Quelccaya glacier, Peruvian Andes: retreat of 3 m a year in the 1970s had increased to 30 m annually by the 1990s.


Three Antarctic ice shelves - Wordie, Larsen A and Prince Gustav - have disintegrated within the last decade. Worldwatch says: "Antarctica's vast land ice is also melting, although there is disagreement over how quickly."

Dr David Vaughan, of the British Antarctic Survey, told BBC News Online: "Overall, not much seems to be happening in Antarctica. "On the Antarctic peninsula, a fairly small area, there is a warming, and that does seem to be having an effect on the ice sheets. "But the meteorological records are very short, and there is a lot of year-to-year variability. There's a lot of argument about whether there really is a warming trend. "And while there are very few people who'll dispute that the peninsula has warmed very rapidly during the last 50 years, we don't know whether this is a global or a regional phenomenon." Positive feedback The Earth's ice cover reflects much of the sun's heat back into space, and Worldwatch says the loss of much of it would affect the global climate, raise sea levels, and threaten water supplies. And it says the land and water left exposed by the retreating ice would themselves retain heat, creating a feedback loop that would speed up the warming process.
It also believes melting ice in the Arctic could release enough fresh water into the north Atlantic to disrupt the Gulf Stream which warms north-west Europe. The Institute says the world's glaciers, taken as a whole, are now shrinking faster than they are growing, and it says the World Glacier Monitoring Service described losses in 1997-98 as "extreme". Worldwatch also warns of the effects of retreating ice on wildlife. In northern Canada, it says, reports of hunger and weight loss among polar bears have been correlated with ice cover changes. And in Antarctica, sea ice loss, rising air temperatures and increased precipitation are altering the habitats and the feeding and breeding patterns of seals and penguins.

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