STEVE INSKEEP, host:

It's MORNING EDITION from NPR News. I'm Steve Inskeep.

(Soundbite of music)

INSKEEP: In off the ice cap that's on top of the gigantic island of Greenland were the melt tomorrow, sea levels around the world would rise by more than 20 feet. The good news is that Greenland isn't going to melt in a flash. The bad news is Greenland is slowly starting to release its water into the ocean in response to rising air temperatures.

For our year-long series Climate Connections with National Geographic, NPR's Richard Harris traveled to Greenland this past summer. He followed scientists trying to figure out how quickly we could be in trouble.

(Soundbite of ice dropping in the sea)

RICHARD HARRIS: This is Greenland's ice as it tumbles into the sea. The Jakobshavn glacier on the island's west coast is quite a sight. Huge mountains of ice — icebergs — clog a narrow fjord and slowly but surely push their way out toward the open ocean.

Eighty percent of this island is covered with one enormous ice sheet, and it oozes off the edges of the island as so-called outlet glaciers. Jakobshavn is among the biggest. And scientist Ian Joughin says in the past few years, Jakobshavn's speed has doubled.

Dr. IAN JOUGHIN (Scientist, University of Washington): That's putting about twice as much ice into the fjord as a decade ago, and twice as much as into the ocean.

HARRIS: And twice as much into the ocean.

And Joughin says Jakobshavn is by no means alone.

Dr. JOUGHIN: Many of the glaciers, especially along the southeast coast of Greenland, are doing very similar things, and what's kind of scary is that they all started doing them roughly at the same time.

HARRIS: That speed-up was triggered by a spell of unusually warm weather here, and that has raised alarms about Greenland. Before that warm-up and speed-up, scientists had thought Greenland's ice would be around for at least a thousand years. Now they're not so sure.

Joughin has come to Greenland with a colleague, Sarah Das, to figure out what is going on under the ice that's contributing to its slide toward the sea. Das says that's a challenge.

Dr. SARAH DAS (Geologist, Woods Hole Oceanographic Institution): It's not like you can go up and sort of poke your head under the ice and see what's happening. It's underwater in many places, completely inaccessible.

HARRIS: The story of sliding ice actually starts dozens of miles inland. In summer, some of the ice up there melts, that water forms lakes and most of those lakes drain through mysterious passages called moulins, which carry the water to the bedrock below the ice.

Once the water gets under the ice, it lubricates the ice sheet, and the whole sheet flows faster toward the sea. That's what Das and Joughin have come here to study.

(Soundbite of helicopter engine humming)

HARRIS: So the next day they fly by helicopter away from the coast and up onto the island's expansive ice cap.

Dr. JOUGHIN: We're going to land on this side of the lake.

HARRIS: The helicopter comes low and the pilot is nervous. The ice here, about 50 miles from the coast, seems to be riddled with holes like Swiss cheese. But Joughin reassures him the holes are only round puddles about a foot deep and the ice itself is a solid block, half-a-mile thick.

Dr. JOUGHIN: Just go for the sort of higher and dryer spot.

HARRIS: The helicopter lands near an automated research station Joughin had set up the previous summer. We pitched our tents and stowed cases of gears, then Joughin and Das head up to service their scientific instruments. These have been recording weather, ice-quakes and more gradual movements of the ice.

Dr. DAS: And we ready for the drill?

Dr. JOUGHIN: Yeah.

Dr. DAS: Okay.

HARRIS: They need to re-anchor the station into the ice because Greenland's entire ice sheet is moving.

Ian Joughin, from the University of Washington, pulls out his GPS unit and finds that this region has slid more than a hundred yards closer to the ocean over the past year. Next he picks up a length of fishing line that he had sunk straight down into the ice last summer. A lot of the line he had buried is now lying on the surface. He measures it to see how much of the ice here has melted away.

Dr. JOUGHIN: Wow. It's a meter and a half of melt since last year.

HARRIS: I think that's almost five feet. Yeah.

Dr. JOUGHIN: Almost five feet. Yeah.

HARRIS: Greenland's ice sheet deforms constantly, like pancake batter flowing on a griddle. Each year, more snow piles up in the middle, and each year, more ice slides off into the sea or melts away.

At the moment, Greenland's melt water increases global sea level by about a quarter of an inch per decade. And if that melt increases as the world warms, a melting Greenland will eventually eat away the shorelines of the world.

(Soundbite of walking on ice)

Sarah Das, who is from the Woods Hole Oceanographic Institution, and Ian Joughin are trying to figure out how quickly that could happen. They pick their way down to the shore of the lake. They side-step water-filled pockets and clamber over hummocks of ice. There are rushing streams everywhere.

Dr. DAS: There's a good place to cross this one is where there's a little island up there.

(Soundbite of water splashing)

HARRIS: We skirt large chunks of ice that you'd say were a beach, if this lake had a beach, flaked some of these bergs look like icicles, and they fall off easily.

(Soundbite of iceberg falling off)

HARRIS: Can iceberg (unintelligible) out of this?

Dr. JOUGHIN: Yeah.

HARRIS: Lake Iceberg.

Dr. JOUGHIN: Look at the (unintelligible).

(Soundbite of water flowing)

HARRIS: We get to the shore of the startlingly blue lake and stand next to a torrent that's bringing melt water down from the surrounding hills of ice.

(Soundbite of water flowing)

HARRIS: Small shards of ice float in an eddy (unintelligible) shore.

Dr. DAS: Those are real rapids. It's coming down that hill.

HARRIS: That inflow is keeping this lake full, but Das says it's only a temporary state of affair.

Dr. DAS: The lakes serve as a reservoir. They collect probably a large fraction in these areas of all the surface melt water and pool them all together as you see. It's really vast and deep, the blue lake that we're standing by.

HARRIS: And when this reservoir drains, the water will flow to the bottom of the ice sheet, where it will essentially grease the underside of these vast sheets of ice making this entire region slide faster toward the coast.

The mystery of this lake is how the water makes its way from here to the bedrock below. Das and Joughin have done some reconnaissance, which suggests that the water is draining out from the far end of the lake, more than a mile away. So we hiked over there with a graduate student named Maya Mathias(ph) from Woods Hole.

Dr. JOUGHLIN: Don't get too close.

Ms. MAYA MATHIAS (Graduate Student, Woods Hole Oceanographic Institution): Oh, my God. It's huge.

HARRIS: And so here we are at the far end of the lake, and the water just cuts down very rapidly at the end and forms a huge stream of about 15 or 20 feet wide, and it heads down the series of incredibly fast rapids and ends up in a hidden channel that's snaking around and going down somewhere.

(Soundbite of trekking)

HARRIS: We head uphill next to the stream, which, meanwhile, is cutting a deeper and deeper canyon. We're going up, it's going down.

(Soundbite of trekking)

HARRIS: We're starting to hear a roar from over there.

Dr. JOUGHLIN: You could see the big cut right there.

(Soundbite of water flowing)

Dr. JOUGHLIN: It's amazing. This feature was probably not here two years ago. Right now, there's maybe a 60-foot deep channel filled with a roaring waterfall. It's sending probably chopped, something like 3,000 feet into the ice.

HARRIS: A few minutes later, the roaring river seems to come to a stop.

That is utterly amazing. Where is that water going?

Ms. DAS: It is. I don't know where the water is going. My guess is that it's going to the bottom of the ice sheet. Right before it disappears from view, it takes some huge jump down, and as far as we've dared to creep to the edge and look down, you see it cascading almost 45 degrees or even steeper downwards into the ice with this thundering roar.

HARRIS: This is the long-sought moulin, the link between the melting ice up here on the surface and the invisible world below.

Okay, I am not going to get too close to the edge. I am very nervous being right this close to a hole that's about 3,000-feet deep. I am going to try an experiment, which is I have a mike on a 40-foot long cable, and I'm going to try to toss the mike over the edge to get a better sound, so here goes.

(Soundbite of water flowing)

HARRIS: This is thrilling.

Ms. DAS: Yeah. It is quite, quite an exciting discovery.

HARRIS: And there are hundreds more like these across Greenland, all speeding the flow of ice toward the sea.

Richard Harris, NPR News.

INSKEEP: You can get a look at Greenland's changing ice sheet at npr.org/climateconnections, and there you can also get coverage of thawing landscapes from National Geographic magazine.

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