Estimates of the rate of ice loss from Greenland and West Antarctica, one of the most worrying questions in the global warming debate, should be halved, according to Dutch and US scientists.
In the last two years, several teams have estimated Greenland is shedding roughly 230 gigatonnes of ice, or 230 billion tonnes, per year and West Antarctica around 132 gigatonnes annually.
Together, that would account for more than half of the annual three-millimetre (0.2 inch) yearly rise in sea levels, a pace that compares dramatically with 1.8mm (0.07 inches) annually in the early 1960s.
But, according to the new study, published in the September issue of the journal Nature Geoscience, the ice estimates fail to correct for a phenomenon known as glacial isostatic adjustment. This is the term for the rebounding of Earth's crust following the last Ice Age.
Often ignored or considered a minor factor in previous research, post-glacial rebound turns out to be important, says the paper.
These revealed, among other things, that southern Greenland is in fact subsiding, as the crust beneath it is pulled by the post-glacial rebound from northern America. These variations show a large degree of uncertainy, but Vermeersen believes that even so a clearer picture is emerging on icesheet loss.
"The corrections for deformations of the Earth's crust have a considerable effect on the amount of ice that is estimated to be melting each year," said Vermeersen, whose team worked with NASA's Jet Propulsation Laboratory and the Netherlands Institute for Space Research.