Recently we learned that the Jakobshavn Glacier, one of Greenland’s fastest sliding, may  have just lost the biggest piece of ice that scientists have yet seen — on the order of 5 square miles in area on its surface. Perhaps the most troubling thing is that scientists don’t even know if that’s a record: Greenland is incompletely monitored, so they can’t really say for sure.

It’s just the latest evidence of how this vast sheet of Northern Hemisphere ice — second in size only to Antarctica — is rapidly losing mass.

Recent research suggests that Greenland is losing 378 gigatons — or, 378 billion metric tons — of ice each year. It takes 360 gigatons to raise sea level by one millimeter, so Greenland is doing that roughly annually. Greenland contains enough ice to eventually raise sea levels by 20 feet, were it all to be lost.

The ice loss is not only from Greenland’s outlying glaciers, in large calving events that can be as big as a gigaton at a time. The ice sheet is also melting on top, as large glacial lakes form on its surface and sometimes drain rapidly through the ice sheet down to its base, further lubricating its flow into the sea.

Here, in pictures, are some dramatic recent images capturing Greenland’s melt:

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