RENEE MONTAGNE, HOST:
Scientists studying the Arctic say it is warming twice as fast as the rest of the planet. And they warn there are no signs of that trend letting up. NPR's Christopher Joyce has the story on the government's annual Arctic report card.
CHRISTOPHER JOYCE, BYLINE: There are no grades for the Arctic in this report card. It's more of a progress report.
JACKIE RICHTER-MENGE: We really see the power of persistence in the Arctic.
JOYCE: Jackie Richter-Menge is a polar scientist with the U.S. Army Corps of Engineers.
RICHTER-MENGE: In this particular case, persistence in the warming air temperatures and the impact that that's having on this icy environment.
JOYCE: Richter-Menge is one of more than 60 researchers from over 13 countries who collaborated with the National Oceanic and Atmospheric Administration on the report. Their conclusion...
RICHTER-MENGE: It's warming in the Arctic faster than it is anywhere on the globe.
JOYCE: That's because of Arctic amplification. Here's how it works. Normally, snow and ice cool the surface by reflecting a lot of the sun's energy back up into the atmosphere. But warming melts snow and ice.
RICHTER-MENGE: And when they melt, they expose darker regions.
JOYCE: Darker regions underneath absorb more heat, like a dark shirt on a hot, sunny day. Same thing when sea ice melts; the exposed water is darker and warms up. So what happens as a result of this amplification? Well, warmer water affects what lives in it. Apparently, plankton like it warmer. They're thriving. Unlike plankton, though, polar bears need cold water and sea ice.
RICHTER-MENGE: There's a strong connection between what's going on with regard to the sea ice cover and the polar bears.
JOYCE: Where the sea ice is holding steady, bears are doing OK. Where the ice is gone, bear numbers are down. Then there's Greenland. The giant landmass is covered in ice that's a mile thick. Geophysicist Bea Csatho at the University of Buffalo has just completed the most comprehensive satellite survey of that ice cover.
BEA CSATHO: There are some places where, in the last 20 years, the ice surface is just lowering, lowering, lowering very uniformly.
JOYCE: Csatho, whose research appears separately in the Proceedings of the National Academy of Sciences, says she's noticed something else about Greenland's blanket of ice. Because the ice melts from the top down, the surface elevation gets lower over time. And at lower elevations, the air generally is warmer.
CSATHO: As Greenland is losing ice, it gets more and more irreversible because you get the ice into lower and lower elevations.
JOYCE: The research shows some exceptions to the warming trend - places where ice is building back or temperatures are cooling. But overall, warming is winning in the Arctic. Christopher Joyce, NPR News.
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