Greenland’s ice sheet may have shrunk past the point of return, with the ice likely to melt away no matter how quickly the world reduces climate-warming emissions, new research suggests.

Scientists studied data on 234 glaciers across the Arctic territory spanning 34 years through 2018 and found that annual snowfall was no longer enough to replenish glaciers of the snow and ice being lost to summertime melting.

That melting is already causing global seas to rise about a millimeter on average per year. If all of Greenland’s ice goes, the water released would push sea levels up by an average of 6 meters — enough to swamp many coastal cities around the world. This process, however, would take decades.