Greenland, home to about a tenth of the world’s ice, might be melting. Data from the dual-spacecraft GRACE project (the Gravity Recovery and Climate Experiment) revealed a dramatic loss of between 150 and 250 cubic kilometres of ice per year between 2002 and 2006. But other indicators have been contradictory and there is the vexed question of just what effect such melting would have on global sea level. In a News Feature this week Alex Witze attempts to pin down the current consensus on just what is going on in Greenland by posing three closely linked questions. The first is whether the warming already “in the pipeline” as a result of todayÂ’s carbon dioxide will warm tomorrowÂ’s oceans sufficiently to push the ice sheet past a point of no return. The second is, how far from that threshold are we? The third is, as time goes on, how much faster will the melt go? Assumptions that such processes take millennia are now being re-examined on the basis of the changes already seen. [News Feature p. 798] Cover graphic by Danny