Global warming at the Poles

Changes in polar ice sheets and glaciers bear testimony to the warming planet

In this July 19, 2011 photo, a cloud drifts past the ever-collapsing calving 6-kilometer-wide (4-mile-wide) front of Jakobshavn Glacier, situated at the edge of the vast Greenland ice sheet, near Ilulissat, Greenland. Greenland is the focus of many researchers trying to determine how much its melting ice may raise sea levels. AP