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Encore: I Spy, Via Spy Satellite: Melting Himalayan Glaciers

AILSA CHANG, HOST:

Scientists have figured out how fast the glaciers in the Himalayan Mountains are melting. What they found is notable, but what's also notable - how they found it. Here's NPR's Pien Huang.

PIEN HUANG, BYLINE: It starts with spy satellites.

SUMMER RUPPER: These satellites are, of course, put up to, essentially, peer over the Iron Curtain.

HUANG: Summer Rupper from the University of Utah says that high-resolution spy satellites were launched during the Cold War to take pictures of hard to reach places on earth. Some of that data has been declassified in the last decade, and so Rupper and her colleagues are using those images to figure out what glaciers in the Himalayas looked like back in the 1970s and '80s. Joshua Maurer of Columbia University is the lead author on their new study in Science Advances. He says that having a historical record is super useful.

JOSHUA MAURER: Glaciers - they can respond to climate over time scales that are fairly long, and so the fact that we can look back further in time several decades ago really helps us pin down how they are responding to the climate.

HUANG: They compare the spy satellite data with images taken in the last 20 years, and they found that the glaciers in the Himalayas have been losing 20 inches of ice a year. That means they're melting twice as fast now as they were in the '80s and '90s. The Himalayas glaciers supply fresh water for billions of people in South Asia. More than half of those glaciers are projected to melt in the next 80 years because of climate change. Rupper says that she's glad this data is out there and available to researchers. It's a treasure trove for scientists.

RUPPER: Essentially what we're doing is capturing the changes in the terrain. So you could do this for landslides, you could do it for volcanic eruptions. We focused on glaciers, but these images are useful for any sort of land surface changes that people might be interested in over time.

HUANG: Other researchers have used spy satellite images to look at ice cover in the Arctic, streams in the Antarctic and meteor paths. Pien Huang, NPR News. Transcript provided by NPR, Copyright NPR.