this is, as we say, not ideal:

Why it matters: The study reveals that seawater is intruding deep into northwest Greenland’s Petermann Glacier, thinning the ice from below.

Petermann acts like a doorstop, holding back vast quantities of land-based ice. As the glacier thins, inland ice moves faster into the ocean, raising global sea levels. If all that inland ice were to melt, it would raise global sea levels by about 1.6 feet, the study found.