Earth: Melting in the Heat?
Glaciers are melting; the ice caps are disappearing into the oceans; sea levels may rise by many meters as a consequence．Indigenous(本土的) Arctic peoples will find their food stocks gone, while flesh water supplies in Asia and south America will disappear as the glaciers which provide them melt away; penguins, polar bears and seals will find their habitats gone, their traditional lives unlivable.
But how realistic is this picture? Is the world's ice really disappearing, or is it unscientific hot air?
A European satellite named Cryosat was designed to provide definitive answers to some of these questions．A launcher fault destroyed the mission in October 2005, hut the European Space Agency has approved a replacement, in the meantime, here is our global snapshot.
The Antarctic
Huge, pristine(质朴的), dramatic, unforgiving--the Antarctic is where the biggest of all global changes could begin.
There is so much ice here that if it all melted, sea levels globally would rise hugely-perhaps as much as 80m．Say goodbye to London, New York, Sydney, Bangkok...in fact, the majority of the world's major cities.
But will it happen? Scientists divide the Antarctic into three zones: the east and west Antarctic ice sheets; and the Peninsula, the tongue of land which points up towards the southern tip of South America.
'Everybody thinks that the Antarctic is shrinking due to climate change, but the reality is much more complex,' says David Vaughan, a principal investigator at the British Antarctic Survey in Cambridge, U.K．'Parts of it appear to be thickening as a result of snowfall increases, but the Peninsula is thinning at an alarming rate due to warming．The West Antarctic sheet is also thinning, and we're not sure of the reason why.'
On the Up
Temperatures in the Peninsula appear to be increasing at around twice the global average—about 2℃ over the last 50 years．Those figures are based on measurements made by instruments at scientific stations.
Earlier this year, David Vaughan's group published research showing that the vast majority of glaciers along the Peninsula--87% of the 244 studied--are in retreat．The ice dumped into the ocean as the glaciers retreat should not make much difference to global sea levels--perhaps a few centimeters.
More worrying, potentially, are the vast ice sheets covering the rest of Antarctica． temperature measurements for the continent as a whole is difficult; it is a vast place--more than 2,000 km across---there are few research stations, and temperatures vary naturally by 2-3 ℃ from year to year．But measurements indicate that in the west, melting is underway.
'About one-third of the West Antarctic ice sheet is thinning,' says Dr．Vaughan, 'un average by about 10 cm per year, but in the worst places by 3～4m per year.'
The rock on which the West Antarctic ice rests is below sea level, and British Antarctic Survey researchers believe the thinning could be due to the ice sheet melting on its underside.
'It may be that the ocean is warming end that's causing the ice to melt, but there may be other reasons as well; for example, there's lots of volcanism in that area and so that could change how much heat is delivered to the underside of the ice sheet.'
Cryosat should help to pin down what is happening at the West Antarctic fringe．The radar altimeters on board its predecessors ERS1 and ERS2 have been unable to map the steep slopes at the coast, whereas Cryosat's instrument should be able to cope.
If the entire West Antarctic ice sheet did melt, sea levels globally would rise, by around 5m．But at the moment, there is no sign of that happening.
One recant scientific paper attempted to calculate probabilities for how much West An