Metal canisters filled with top-secret satellite photos plummeted from space and then parachuted over the Pacific Ocean during the '70s and '80s. A U.S. Air Force plane would swoop down on cue and snag the classified material, ferrying the images safely back to land.
The spy satellite missions, run by the National Reconnaissance Office, sought to capture wide-ranging views of what transpired around the globe. In all, they photographed some 877 million square miles of Earth. The black and white photos, now declassified, have great scientific value: They reveal the accelerated melting of the colossal Himalayan glaciers — home to the third largest ice sheets on the planet.
In new research published Wednesday in the journal Science Advances, earth scientists used this Cold War-era imagery to conclude that ice melt in the Himalayas has doubled since the year 2000, compared to the quarter-century prior.
"We have imagery from the 1970s that shows what the glaciers were like back then," said Joshua Maurer, lead author of the study and a Ph.D. candidate at Columbia University’s Lamont-Doherty Earth Observatory.
Image: National Museum of the U.S. Air Force
But since 2000, temperatures in the region, home to the highest elevations on Earth, have risen by 1.8 degrees Fahrenheit (or 1 degree Celsius). That's enough to amplify ice melt, especially at the lower portions of glaciers which are already prone to melting.
"It's a region that's very vulnerable to climate change," added Maurer.
The spy images further underscore the reality of accelerated glacier melt around the planet. Each year, Earth is now losing the equivalent of three times the amount of ice in the European Alps. In Montana in the mid-1800s, there were an estimated 150 sizable glaciers in what is now Glacier National Park. Today, there are just 26 glaciers large enough to be counted.
Image: National Reconnaissance Office
In short, Earth is feeling the effects of accelerating climate change.
"We’re not trying to figure out whether the glaciers will melt in the future," said Alex Gardner, a NASA glaciologist who had no role in the study. "We're just trying to find out how much and how fast."
Using the spy photos, Maurer looked at around 650 Himalayan glaciers and converted them into 3D imagery to create an improved idea of what the glaciers looked like, some 40 years ago. In recent decades, the loss of ice is stark, and temperature increases are the conspicuous, repeatedly observed link.
"We know there is a very strong link between temperature changes and glacier melt," said Gardner. "Every single glacier region on Earth is losing mass."
These days, the National Reconnaissance Office no longer needs to drop literal photographic reels from hundreds of miles above. Satellites now directly transmit data to Earth. And this satellite imagery, generally speaking, is invaluable. It's impossible to get a grip on glacier melt and trends without eyes in space.
"It takes days to trek up through the glaciers carrying scientific equipment," noted Maurer, who visited the Himalayas a couple of years ago. What's more, many important glaciers are in politically unstable regions and the extreme, disorienting conditions at high altitude make it difficult to even measure one glaciated area, he explained.
Even in the best case scenarios — should civilization collectively slash its accelerating carbon emissions — the greater Himalayan region is expected to lose a third of its ice by century's end — but it's likely this number will be considerably more. Such ice loss doesn't bode well for the hundreds of millions that depend on Himalayan glaciers for their water and livelihoods.
For now, scientists will watch the melt — using today's (fortunately) unclassified satellite images.
"The ice loss will continue to accelerate," said Maurer.