A study reveals that the renowned Himalayan glaciers have lost over 40% of their area, threatening millions of people in Asia with lack of water availability
The study, led by the University of Leeds, notes that in recent decades the Himalayan glaciers have lost ice around ten times faster over the last few decades, than on average since the last Little Ice Age expansion 400 to 700 years ago.
The Himalayan Mountain range the world’s third-largest amount of glacier ice, after Antarctica and the Arctic, but the rapidly shrinking Himalayan glaciers have been shown to be melting far faster than glaciers in other parts of the world.
Shrinking from their peak of 28,000 km2 to currently, only 19,600 km2
This study, published in Scientific Reports, made a reconstruction of the size of the ice surfaces of 14,798 Himalayan glaciers during the Little Ice Age, which was the last major glacier expansion. The researchers estimated that the glaciers have lost around 40% of their area.
Within this period, the glaciers have additionally lost between 390 km3 and 586 km3 of ice, which is the equivalent of all the ice contained today in the central European Alps, the Caucasus, and Scandinavia combined.
The researchers calculated that the water released through the glaciers melting has been predicted to have raised sea levels globally by between 0.92 mm and 1.38 mm.
Using satellite images and digital elevation models to produce outlines of the glaciers’ magnitude 400-700 years ago and to ‘reconstruct’ the ice surface. The satellite images displayed ridges that mark the former glacier boundaries, and the researchers used the geometry of these ridges to estimate the former glacier size and ice surface elevation.
They determined the volume and consequential mass loss between the Little Ice Age and now by comparing the glacier reconstruction to the glacier now.
Dr Jonathan Carrivick, corresponding author and Deputy Head of the University of Leeds School of Geography, said: “Our findings clearly show that ice is now being lost from Himalayan glaciers at a rate that is at least ten times higher than the average rate over past centuries.
“This acceleration in the rate of loss has only emerged within the last few decades, and coincides with human-induced climate change.”
Researchers describe the loss of ice as “exceptional”
This shrinkage has significant implications for hundreds of millions of people who depend on Asia’s major river systems for food and energy, as seen with the rivers Brahmaputra, Ganges and Indus.
The Himalayan glaciers are generally losing mass faster in the eastern regions – taking in east Nepal and Bhutan north of the main divide. It is suggested that this variation is most likely due to differences in geographical features on the two sides of the mountain range, and their interaction with the atmosphere which results in different weather patterns.
Himalayan glaciers are also declining and ending in lakes, which have several warming effects, as opposed to ending on land. The amount and sizes of lakes in this region are increasing so continued acceleration in mass loss can be expected.
Correspondingly, glaciers with significant amounts of natural debris on their surfaces also continue to lose mass more quickly, contributing around 46.5% of total volume loss despite making up only around 7.5% of the total number of glaciers.
Dr Carrivick stated: “While we must act urgently to reduce and mitigate the impact of human-made climate change on the glaciers and meltwater-fed rivers, the modelling of that impact on glaciers must also take account of the role of factors such as lakes and debris.”
Co-author Dr Simon Cook, Senior Lecturer in Geography and Environmental Science at the University of Dundee, added: “People in the region are already seeing changes that are beyond anything witnessed for centuries.
“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.”