Melting Rate of Icecaps in Greenland and Western Antarctica Lower Than Expected

Some good news for a change. Or at least, it's less bad :)

http://www.sciencedaily.com/releases/2010/09/100906085152.htm

ScienceDaily (Sep. 7, 2010) — The Greenland and West Antarctic ice caps are melting at half the speed previously predicted, according to analysis of recent satellite data.

The finding is the result of research by a joint US/Dutch team from the Jet Propulsion Laboratory, Delft University of Technology (TU Delft, The Netherlands) and SRON Netherlands Institute for Space Research. The scientists have published their work in the September issue of Nature Geoscience.

GRACE

The melting of the ice caps has been charted since 2002 using the measurements produced by the two GRACE satellites. From space they detect small changes in the Earth's gravitational field. These changes are related to the exact distribution of mass on Earth, including ice and water. When ice melts and lands in the sea, this therefore has an effect on the gravitational field.

Based on this principle, previous estimates for the Greenland ice cap calculated that the ice was melting at a rate of 230 gigatonnes a year (i.e. 230,000 billion kg). That would result in an average rise in global sea levels of around 0.75 mm a year. For West Antarctica, the estimate was 132 gigatonnes a year. However, it now turns out that these results were not properly corrected for glacial isostatic adjustment, the phenomenon that the Earth's crust rebounds as a result of the melting of the massive ice caps from the last major Ice Age around 20,000 years ago. These movements of the Earth's crust have to be incorporated in the calculations, since these vertical movements change the Earth's mass distribution and therefore also have an influence on the gravitational field.

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One of the researchers, Dr Bert Vermeersen of TU Delft, explains: "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. We have concluded that the Greenland and West Antarctica ice caps are melting at approximately half the speed originally predicted." The average rise in sea levels as a result of the melting ice caps is also lower.

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