From Yahoo Singapore: It may be that any perceived melting of the icecap is the cause, not of warming per se, but other more important factors, and that glaciers have been retreating for 20,000 years now:
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.
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.
With glacial isostatic 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.
These variations show a large degree of uncertainty, but Vermeersen believes that even so a clearer picture is emerging on icesheet loss.