At the top of the world, northern Greenland’s huge glaciers — long thought to be relatively stable — are in trouble, a new study shows.

As the ocean warms, Greenland’s last remaining ice shelves are rapidly weakening, destabilizing the nearby glaciers and threatening potentially “dramatic” consequences for sea level rise, according to the study published Tuesday in Nature Communications.

Ice shelves are tongues of floating ice that jut out over the ocean and act as dams that hold back glaciers on land and slow ice loss. When they melt and weaken, more of the land-based ice is able to slide into the ocean, adding to sea level rise.