John R. Platt writes: Greenland’s melting ice sheets are contributing more water to the oceans than previously realized, and that’s going to lead to even greater amounts of sea-level rise around the world, according to new research.

The paper, published in the journal Nature Climate Change, reveals something scientists wouldn’t have expected just five years ago. “It’s a very rapid change,” said one of the study’s authors, William Colgan of York University in Toronto. “The ice sheet is now losing about 8,000 tons every second, year-round, day in and day out.”

Colgan said the “lion’s share” of that loss—about 5,000 tons per second—comes in the form of meltwater. The ice sheet, like a sponge, used to be able to absorb most of what melted each year because the uppermost layers are composed of tightly packed but permeable snow, as opposed to the impermeable layers of ice much farther below. That porous surface, called “firn,” normally would allow meltwater to sink downward, where it would refreeze and stay within the glacier.

That started changing about a decade ago. [Continue reading…]