What Greenland's 'unprecedented' ice loss means for Earth

For a few days in July of 2012, it was so hot in the Arctic that nearly the entire surface of the Greenland ice sheet turned to slush.

It was so uncharacteristically warm that scientists, emerging from their tents high on the peak of the ice sheet, sank up to their knees in the suddenly soft snow. And then, that snow started melting.

Near the edge of the ice sheet, bright blue puddles collected on the flat white surface. Rivulets of melt trickled down, braiding into fat, gushing rivers. The meltwater punched through gullies and spilled down crevasses. One river near the edge of the ice sheet was so swollen that it swept away a bridge that had been there for decades. So much water spilled out of the guts of the ice sheet that year that global sea levels rose by over a millimeter.

The melting was alarming, like nothing scientists had seen before. But no one knew exactly how unusual the event was or how worried to be. But now, scientists have figured out that the hot 2012 summer capped off 20 years of unprecedented increases in meltwater runoff from Greenland. And even more concerningly, they found, melting is speeding up even faster than air temperatures warm. So yes, they found, 2012 was a particularly bad year—but it was just a preview of what might come.

“The melting of the Greenland ice sheet is greater than at any point in the last three to four centuries, and probably much longer than that,” says Luke Trusel, a researcher at Rowan University in New Jersey and lead author of the new study, published today in Nature.

And the effects of the melting aren’t just abstract: A complete melting of Greenland’s mile-thick ice sheets would dump seven meters (23 feet) of extra water into the world’s ocean. So what happens high in the poles matters to anyone who lives near a coast, eats food that comes through a coastal port, or makes a flight connection in an airport near the ocean, scientists warn.

Scientists already knew that Greenland was melting fast; they could track its shrinking size from satellites. But the key satellite data only goes back until the early 1990s—so they couldn’t tell exactly how alarmed to be by the melting. Had this kind of jaw-dropping warming happened before? How unusual was it, compared to the time before human-caused climate change kicked into gear? No one knew.

To continue reading: https://www.nationalgeographic.com/environment/2018/12/greenland-ice-sheet-is-melting-faster-than-in-the-last-350-years/