Many climate scientists felt the conclusions on effects of global warming in the 2007 IPCC review were too conservative. One reason was the estimation of likely melting of ice sheets and its effects.
Problem was that there was insufficient knowledge to draw definite conclusions. And the measurements of changes in ice sheets just wasn’t accurate enough.
That’s now changed and a large number of experts agree global warming has caused loss of ice from these ice sheets. And this has contributed to measured increases in sea level.
Richard A. Kerr reports in Science (see Experts Agree Global Warming Is Melting the World Rapidly):
“Forty-seven glaciologists have arrived at a community consensus over all the data on what the past century’s warming has done to the great ice sheets: a current annual loss of 344 billion tons of glacial ice, accounting for 20% of current sea level rise. Greenland’s share—about 263 billion tons—is roughly what most researchers expected, but Antarctica’s represents the first agreement on a rate that had ranged from a far larger loss to an actual gain. The new analysis, published on page 1183 of this week’s issue of Science, also makes it clear that losses from Greenland and West Antarctica have been accelerating, showing that some ice sheets are disconcertingly sensitive to warming.”
He’s referring to the major paper by Andrew Shepperd and others, A Reconciled Estimate of Ice-Sheet Mass Balance.
Over recent years climate change deniers/contrarians/sceptics have cherry picked data to counter any suggestion that the earth’s large ice sheets are melting. They have pointed to increased amounts of ice in Eastern Antarctica to balance reports of massive losses of ice in the Arctic. (Have a look at this animation to see how such data can be cherry picked). Similarly they have tried to hide concern of the loss of land ice by stressing reports of local increases in sea ice.
But the paper by Shepperd et al. combined data from satellite altimetry, interferometry, and gravimetry measurements. This provides more reliable estimates of changes in the ice sheets, and gives some detail of these changes. This figure from the paper gives an idea of the detail of their findings. It shows that all the major regions of the polar ice sheets except one (East Antarctica) have lost mass since 1992. The authors also estimate that mass loss from the polar ice sheets has contributed roughly 20 percent of the total global sea level rise during that period (at a rate of 0.59 ± 0.20 millimeter year−1 ).
Figure S1 from Shepperd et al.: Cumulative ice mass change of West Antarctica ((WAIS) East Antarctica (EAIS), Greenland (GrIS), and the Antarctic Peninsula (APIS).
And to underline the fact that denier claims of amounts of ice increasing in Antarctica are false, NASA recently displayed this figure showing data from Antarctica from their satellite measurements