Greenland's ice on the scales

摘要

Satellite measurements of changes in Earth's gravity field reveal ice loss from Greenland's ice sheet, Over the past four years, this melt has contributed to global sea-level rise at an accelerating rate. The volume of the ice sheet that covers most of Greenland is so large that, were it to melt completely, sea levels across the world would rise by about 7 metres. urthermore, an increase in its delivery of fresh water to the oceans could weaken or disrupt the 'thermohaline' circulation of oceanic salt water1, profoundly altering the climate of the Northern Hemisphere. Such doomsday scenarios are well rehearsed, but - expressed in this way - not necessarily accurate. If cold areas such as the centre of Greenland warm up, it might actually snow more.That would, in turn, thicken the ice sheet and remove water from the global oceans. The very different densities of snow, ice and water mean that measuring the volume of the Greenland ice sheet does not provide the complete answer as to whether it is growing or shrinking. The ideal method is to measure how the mass of the ice sheet is changing with time.