Himalayan glaciers are losing ice at an “exceptional” speed that threatens the water supply for millions of people and adds to the threat from climate change, scientists have found.
The glaciers lost ice 10 times more quickly over the past few decades than on average since the last major glacier expansion during the Little Ice Age between 400 and 700 years ago, the study published in Scientific Reports said.
The study also found that glaciers were shrinking far more rapidly than glaciers in other parts of the world, a rate of loss the researchers called “exceptional”.
The Himalayas is the third largest reservoir of ice on the planet after the Arctic and Antarctic, and ice lost there has ripple effects in rising sea levels around the world.
“Our findings clearly show that ice is now being lost from Himalayan glaciers at a rate that is at least 10 times higher than the average rate over past centuries,” said Dr Jonathan Carrivick, corresponding author from University of Leeds's School of Geography.
“This acceleration in the rate of loss has only emerged within the last few decades, and coincides with human-induced climate change.”
Researchers made a reconstruction of the size and ice surfaces of 14,798 Himalayan glaciers during the Little Ice Age.
They then calculated that the glaciers have lost about 40 per cent of their area, shrinking from a peak of 28,000 square kilometres to about 19,600 square kilometres today.
During that period they have also lost between 390km³ and 586km³ of ice, the equivalent of all the ice contained today in the central European Alps, the Caucasus, and Scandinavia combined.
Water released through that melting has raised sea levels across the world by between 0.92mm and 1.38mm, the team calculates.
“People in the region are already seeing changes that are beyond anything witnessed for centuries,” said co-author Dr Simon Cook, from the University of Dundee.
“This research is just the latest confirmation that those changes are accelerating and that they will have a significant impact on entire nations and regions.”
The acceleration of melting of Himalayan glaciers has significant implications for hundreds of millions of people who depend on Asia’s major river systems, which includes the Brahmaputra, Ganges and Indus for food and energy.
Glaciers are generally losing mass faster in the eastern regions, such as east Nepal and Bhutan. The study suggests this variation is probably due to differences in geographical features on the two sides of the mountain range.
They are also declining faster where they end in lakes, which have several warming effects, rather than where they end on land.
The number and size of these lakes are increasing so continued acceleration in mass loss can be expected.
The team used satellite images and digital elevation models to produce outlines of the glaciers’ extent 400-700 years ago and to "reconstruct" the ice surface.