Himalayan meltdown from space
US spy satellites that secretly kept watch over the Himalaya during the Cold War are helping researchers piece together the most detailed view yet of the region’s accelerating ice loss.
The US military used the satellites to take thousands of photographs worldwide as part of its surveillance of the Soviet Union, China and other countries, dating as far back as the 1970s.
Now declassified, the satellite data is helping researchers track the melting of the Himalayan glaciers, and it is revealing changes across the region that scientists say are consistent with global warming. The results could help communities in Nepal, India, China, Bhutan and downstream countries that rely on those glaciers to prepare for future flooding and changes in their water resources as the climate changes.
Scientists analysed images of 650 Himalayan glaciers as the ice changed over four decades and found that, on average, the glaciers melted twice as fast between 2000 and 2016 as they did from 1975 to 2000.
“This is the clearest picture yet of how fast Himalayan glaciers are melting over this time interval, and why,” said Josh Maurer, the study’s lead author at Columbia University’s Earth and Environmental Sciences program.
Comparison of satellite images taken in 1975 and 2007 of the Nepal-India border reveals changes in the elevation of glaciers. Alison Corley / Lamont-Doherty Earth Observatory
The melting was driven by increases in air temperature due to the greenhouse effect, according to the study published Wednesday in the journal Science Advances. Since the melting was consistent across the region, the researchers could not attribute it to more variable, localised effects, such as black carbon, which darkens ice so it absorbs more energy, or precipitation.
“That doesn’t rule out impact by these other sources,” said study co-author Summer Rupper, of the University of Utah. But the evidence suggests warming temperatures are driving the extensive melting, and both are picking up speed.
Being able to track changes over time helps researchers parse out trends connected with global warming. “You remove some of that year-to-year variability and you get what the actual long-term change looks like,” Rupper said.
Until now, researchers have mostly looked at changes in the amount of land the glaciers cover, Rupper said, adding, “but that doesn’t actually tell us how much ice or water is being lost.”
To gauge the change in glacier volume, the scientists created a method to ‘essentially do what our eyes do naturally’, using overlapping images to construct a three-dimensional image of the terrain.
The satellite data spans India, China, Nepal and Bhutan. Each of those countries, in addition to Afghanistan, Bangladesh, Myanmar and Pakistan, are members of the Kathmandu-based International Centre for Integrated Mountain Development (ICIMOD), which has been studying the changes now underway in mountain glaciers.
ICIMOD released an assessment earlier this year stating that, in a best-case scenario, Himalayan glaciers will lose more than one-third of their mass by the end of the century. And if greenhouse gas emissions continue at current rates, two-thirds could be gone.
That melting could have devastating consequences for communities in and near the Himalaya, many of whom already face poverty and malnutrition. Glacier melt adds to those vulnerabilities, threatening floods, landslides and the loss of their water supply.
“With glacier melt, the impact is biggest for mountain communities who are directly dependent on glaciers,” said ICIMOD’s David Molden.
Communities that rely on Himalayan glaciers for water already see the effects of shrinking ice, Molden said. As canals that channel glacier water to communities run dry, they have to dig new ones, higher in the mountains. “You can look at the mountain and kind of see these stripes of canals hitting the glacier,” Molden said.
Researchers hope their findings can create a framework that will help communities adapt to potential changes and hardships as temperatures continue to warm. “What does that change actually mean in terms of downstream water resources? We can give some sense of projections to communities.”
Molden said the spy satellite findings could be important in helping to persuade policymakers to plan for the effects of climate change: “It’s strengthening the case that climate change is coming more rapidly than we expect.”