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Each summer, about half of the surface of the Greenland ice sheet melts. That's on average, but this month, in just four days, an estimated 97 percent of the ice sheet's surface has already melted. That rate is abnormally fast and it comes just a week after a huge iceberg broke off a glacier in Greenland.
For more now, I'm joined by Tom Wagner. He's a scientist at NASA. Hi there, Tom.
TOM WAGNER: Hello.
CORNISH: Now, to start, how'd this come to NASA's attention?
WAGNER: You know, we started hearing reports of extreme melting around Greenland. In fact, my wife, who's the director of the Arctic Logistics Program for the U.S. Arctic Program, said, hey, the bridge is washing out in Kangaloosawac(ph) and their runway that they use to land aircraft on for deep field work was starting to develop cracks and melting. And so she said, tell us what the satellites are seeing. So I contacted my colleagues at NASA and they were amazed to see what was going on.
CORNISH: Now, there's always some degree of ice melt in Greenland. Right? And I read this is being called a natural variation. So what's remarkable about this melting?
WAGNER: What's remarkable is this - is that parts of Greenland that we've never seen melting before melted this year and this is - the Greenland ice sheet is miles thick in places and the central summit area is 12,000 feet above sea level and even that area saw melt. This is a place that never gets above freezing and, this year, they measured temperatures of 42 degrees up there.
CORNISH: So what's worrisome about it?
WAGNER: Well, the important thing is this. There is a lot of natural variation in the climate system and it's what we call weather and an event like this could be within that natural variation. We have ice cores in Greenland that tell us about what Greenland was like thousands of years ago and it looks like something like this happens about every 150 years.
But what's important about this is that, even if it's unrelated to global warming, it's this phenomenal natural experiment for us. You know, like, we've actually got so much water in places that it's coalescing into rivers and lakes and ponds that are flowing out. Some of that stuff is also percolating down to the bed and it may lubricate how fast the ice flows.
And, overall, we're trying to get a picture of what we call the mass balance of the ice. How much is being lost and is it being lost by icebergs calving off or is it being lost by melting? And something like this helps us do that so we can improve our long term models.
CORNISH: And you mentioned icebergs calving off and we talked about the Peterman Glacier in Greenland last week. How is this related?
WAGNER: Yeah. Well, they're separate events. In the case of Peterman, you can think of the Greenland ice sheet almost like if you poured a big pile of honey on the table in front of you. Snow builds up in the middle. It gets compacted to ice. That ice flows out towards the coast. Where that ice hits the ocean, it can begin to float and form an ice shelf and that's what's happening in the Peterman area is that ice shelf is breaking off.
Now, that is a natural process, too. It does, though, look like, around Peterman, it could be that the ocean is getting warmer and there's a lot more loss that's happening.
But, overall, we can't lose sight of the big picture, which is this. Greenland is losing a tremendous amount of ice in response to warming. We think it's mostly happening because the ocean around Greenland's getting warmer, but all the glaciers look like they've been speeding up and Greenland is losing 150 gigatons of ice a year over the last 20 years. That corresponds to about a third of a millimeter a year of sea level rise.
CORNISH: That's NASA scientist Tom Wagner. Tom, thank you.
WAGNER: Thank you.
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