Greenland is a giant ice sheet covered in snow. Its snowline — the border where snow cover and bare ice abut — migrates with the seasons, sliding to lower elevations in the winter and shifting up in the summer. Now researchers find that not only does the snowline move much more dramatically than they thought, but it also accelerates melting of the ice sheet.

That’s a problem because the Greenland ice sheet is melting into the ocean and contributing to global sea level rise. The new findin