[Arnt]

I agree that this is probably what the article tries to say.

There is another possibility, though: Maybe it's saying that a large area of Greenland's ice surface is at an elevation where the glaciers are barely staying neutral. If that's what it tries to say, then having all of that area sink by 3m means that a large area goes into decline and stays in a state of decline. The surface sinking by 3m, 10m, 20m or 50m would then be much the same, just different speeds of irreversible decline.