ananyo writes "A global team of researchers has come up with the most accurate estimate yet for melting of the polar ice sheets, ending decades of uncertainty about whether the sheets will melt further or actually gain mass in the face of climate change. The ice sheets in Greenland and Antarctica are melting at an ever-quickening pace. Since 1992, they have contributed 11 millimeters — or one-fifth — of the total global sea-level rise, say the researchers. The two polar regions are now losing mass three times faster than they were 20 years ago, with Greenland alone now shedding ice at about five times the rate observed in the early 1990s. This latest estimate, published this week in Science, draws on up to 32 years of ice-sheet simulations and 20 years of satellite data to give an estimate two to three times more accurate than that in the last IPCC report."