Himalayan glaciers have been melting twice as fast since 2000, posing a threat to water supplies for hundreds of millions of people across Asia, scientists have revealed.
The study published in the Journal of Science Advances on Wednesday combined declassified US spy satellites from the mid-1970s with modern satellite data and 3D mapping tools to create a detailed four-decade record of 650 glaciers in the Himalayas spanning 2,000km.
The research shows that between 1975 and 2000, the glaciers lost an average of 4bn tonnes of ice each year and not replaced by snow. Between 2000 and 2016 the average doubled to approximately 8bn tonnes of ice each year with some lower level glaciers shrinking by 0.5m annually.
Joshua Maurer, from Columbia University’s Lamont-Doherty Earth Observatory, and a lead author on the study said: “This is the clearest picture yet of how fast Himalayan glaciers are melting over this time interval, and why.”
Weather changes and soot deposited from industrial pollution are thought to contribute to local areas of increased melting, however, the Columbia team said that the glaciers shrinking at similar rates along the mountain chain indicate that overall rising temperatures was the main cause.
“The fact we see such a similar spatial pattern of ice loss across so many glaciers across such a large and climatically complex region suggests there needs to be some kind of overall forcing affecting all of the glaciers similarly,” said Maurer.
In the short term, this rapid increase of meltwater can lead to risks of flooding across many regions. Longer term, millions of people who depend on glacier meltwater for water resources, agriculture and hydropower could face real difficulties.
Commenting on the research, Dr Hamish Pritchard from the British Antarctic Survey, said “What’s new here is being able to see how the melting of glaciers across the whole Himalayan range has increased due to climate change.
“Why does this matter? Because when the ice runs out, some of Asia’s most important rivers will lose a water supply that keeps them flowing through drought summers, just when water is at its most valuable.
“Without mountain glaciers, droughts will be worse for millions of water-stressed people living downstream.”