A new study warns that Greenland’s ice is melting faster than scientists previously thought. But perhaps the biggest surprise is that most of this ice loss is from the land-fast ice sheet itself, not Greenland’s glaciers.

The new study, published January 21 in the Proceedings of the National Academy of Sciences, found that the largest sustained ice loss from early 2003 to mid-2013 came from Greenland's southwest region, which is mostly devoid of large glaciers.

Greenland, the world’s biggest island, appears to have hit a tipping point around 2002-2003 when the ice loss rapidly accelerated, said lead author Michael Bevis, a geoscientist at Ohio State University. By 2012 the annual ice loss was “unprecedented” at nearly four times the rate