The Greenland ice sheet is a vast body of ice covering 660,235 square miles, roughly 80% of the surface of Greenland. It is the second largest ice body in the World, after the Antarctic Ice Sheet. The ice sheet is almost 1,500 miles long in a north south direction, and its greatest width is 680 miles at a latitude of 77°N, near its northern margin. Scientists investigating the geophysical and hydrological conditions beneath the Greenland ice sheet say their analysis will be vital for helping understand how the massive ice sheet will respond to climate change.