Picture 3 million Olympic-size swimming pools full of water.
That's how much ice melts from glaciers in the Himalayas each year, a new study suggests, and climate change is the primary cause.
Even more concerning is that the ice melt has doubled in recent years: Himalayan glaciers have been losing the equivalent of more than a foot and half of ice each year since 2000 - which is double the amount of melting that took place from 1975 to 2000.
"This is the clearest picture yet of how fast Himalayan glaciers are melting over this time interval and why," said study lead author Joshua Maurer, a Ph.D. candidate at Columbia University's Lamont-Doherty Earth Observatory.
Overall, the Asian mountain range, which includes Mount Everest, has been losing ice at a rate of about 1% a year since 2000.
The big melt: Global warming predicted to melt massive Himalayan glaciers, disrupt food production
The melting also threatens the water supplies for hundreds of millions of people downstream who rely on it for hydropower, agriculture and drinking, across a large portion of Asia, said study co-author Jorg Schaefer, a climate geochemistry professor at Columbia.
"Disaster is in the making here," Schaefer said.
Scientists used recently declassified Cold-War-era 3D satellite images to track the glacial retreat back to the mid-1970s. By analyzing 650 Himalayan glaciers, the researchers estimate that, of the region's total ice mass present in 1975, 87% remained in 2000, and 72% remained in 2016.
Water, water everywhere: 390 billion tons of snow and ice melts each year as globe warms
Rising temperatures are the primary cause of the melting, the study said, noting that average temperatures in the Himalayas were about 2 degrees warmer from 2000 to 2016 than they were from 1975 to 2000.
The study shows that "even glaciers in the highest mountains of the world are responding to global air temperature increases driven by the combustion of fossil fuels," said Joseph Shea, a glacial geographer at the University of Northern British Columbia who was not involved in the study.
"To stop the temperature rises, we have to cool the planet," Schaefer told the Guardian. "We have to not only slow down greenhouse gas emissions, we have to reverse them. That is the challenge for the next 20 years."
The study was published Wednesday in the peer-reviewed journal Science Advances, a publication of the American Association for the Advancement of Science.
Contributing: The Associated Press
This article originally appeared on USA TODAY: Glaciers, goodbye? Himalayan ice melt has doubled in recent years, old spy images confirm