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Estimates of the rate of ice loss from Greenland and West Antarctica should be halved, say Dutch and US scientists. Since 2002, NASA's Gravity Recovery and Climate Experiment (GRACE) satellite data has been used to make an estimate of ice melt from Greenland and Western Antarctica, says this article by Lewis Page. The rest of Antarctica doesn't seem to be melting at all, says Page. Indeed Antarctica as a whole is actually gaining ice area rather than losing it - but some regions in the West are melting.
According to the new study, previous ice estimates fail to correct for the rebounding of Earth's crust following the last Ice Age. The miles-thick glaciers that smothered Antarctica and most of the northern hemisphere compressed the crust beneath them. When the glaciers started to retreat around 20,000 years ago, the crust began rebounding, and is still doing so. "A good analogy is that it's like a mattress after someone has been sleeping on it all night," said lead researcher Bert Vermeersen of Delft Technical University, in the Netherlands. The weight of the sleeper creates a hollow as the material compress downwards and outwards. When the person gets up, the mattress starts to recover. "We have concluded that the Greenland and West Antarctica ice caps are melting at approximately half the speed originally predicted," said Vermeersen, whose team worked with NASA's Jet Propulsation Laboratory and the Netherlands Institute for Space Research.
With the rebound adjustment modelled in, the loss from Greenland is put at 104 gigatonnes, plus or minus 23 gigatonnes, and 64 gigatonnes from West Antarctica, plus or minus 32 gigatonnes. This translates into less than 2mm of sea-level rise, says Page. "In the case of Greenland, it could be that the current estimates are triple what they should be."
"For Greenland in particular, we have found a glacial isostatic adjustment model that deviates rather sharply from general assumptions," says Vermeersen.
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Here's a statement issued yesterday by Vermeersen's university: The new research can be read here by subscribers to Nature Geoscience, and analysis of it by independent experts can be read (for a fee) here.
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