There have been several estimates that Greenland is shedding roughly 230 billion tonnes of ice and West Antarctica around 132 billion tonnes per year and analysts have been concerned that these rates are much faster than predicted by climate models – suggesting that the models may be far too conservative.
Now researchers from the US Jet Propulsion Laboratory, the Technical University of Delft and SRON Netherlands Institute for Space Research have published research which corrects that estimate for deformation processes occurring in the Earth’s crust.
The researchers used GPS and sea floor pressure measurements to estimate the movement of the Earth’s crust as a result of "post-glacial rebound". This is the expansion of material which was compressed under ice during the last ice age. Most significantly, they have found that movement of the North American continent, which is still rebounding from being under kilometres of ice 10,000 years ago, is causing the sea floor under Greenland to drop.
The adjustments result in rates of ice melt which are roughly half of the previous estimates – the loss from Greenland is put at 104 billion tonnes, plus or minus 23 billion tonnes, and 64 billion tonnes from West Antarctica, plus or minus 32 billion tonnes.