New study reduces estimate of icecap loss

The Independent via AFP: 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. It looks at tiny changes in Earth's gravitational field provided by two satellites since 2002, from GPS measurements on land, and from figures for sea floor pressure.

…"We have concluded that the Greenland and West Antarctica ice caps are melting at approximately half the speed originally predicted." If the figures for overall sea level rise are accurate, icesheet loss would be contribute about 30 percent, rather than roughly half, to the total, said Vermeersen. The rest would come mainly from thermal expansion, meaning that as the sea warms it rises….

Antarctic mountains, pack ice and ice floes, shot by Jason Auch, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license