According to them, the "hotspot" is located in the northeast corner of Greenland -- just below a site where an ice stream was recently discovered.

The researchers don't yet know how warm the hotspot is, but if it is warm enough to melt the ice above it even a little, it could enable the ice to slide more rapidly out to sea.

To measure actual temperatures beneath the ice, scientists will have to drill boreholes down to the base of the ice sheet-- a mile or more below the ice surface. The effort and expense make such measurements few and far between, especially in remote areas of northeast Greenland.

"The behaviour of the great ice sheets is an important barometer of global climate change," said Ralph von Frese, leader of the project and a professor of earth sciences at Ohio State University.

"However, to effectively separate and quantify human impacts on climate change, we must understand the natural impacts, too,” he added.

Von Frese's team combined gravity measurements of the area taken by a Naval Research Laboratory aircraft with airborne radar measurements taken by research partners at the University of Kansas.

The combined map revealed changes in mass beneath the Earth's crust, and the topography of the crust where it meets the ice sheet.