The accelerating melting of the Himalayan glaciers threatens the water
supply of millions of people in Asia, new research warns.
The study, led by the University of Leeds, concludes that over recent
decades the Himalayan glaciers have lost ice ten times more quickly over the
last few decades than on average since the last major glacier expansion
400-700 years ago, a period known as the Little Ice Age.
The study also reveals that Himalayan glaciers are shrinking far more
rapidly than glaciers in other parts of the world—a rate of loss the
researchers describe as "exceptional".
The paper, which is published in Scientific Reports, made a reconstruction
of the size and ice surfaces of 14,798 Himalayan glaciers during the Little
Ice Age. The researchers calculate that the glaciers have lost around 40
percent of their area—shrinking from a peak of 28,000 km² to around 19,600
km² today.
During that period they have also lost between 390 km³ and 586 km³ of
ice—the equivalent of all the ice contained today in the central European
Alps, the Caucasus, and Scandinavia combined. The water released through
that melting has raised sea levels across the world by between 0.92 mm and
1.38 mm, the team calculates.
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."
The Himalayan mountain range is home to the world's third-largest amount of
glacier ice, after Antarctica and the Arctic and is often referred to as
'the Third Pole'.
The acceleration of melting of Himalayan glaciers has significant
implications for hundreds of millions of people who depend on Asia's major
river systems for food and energy. These rivers include the Brahmaputra,
Ganges and Indus.
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. The satellite images revealed ridges that mark the former
glacier boundaries and the researchers used the geometry of these ridges to
estimate the former glacier extent and ice surface elevation. Comparing the
glacier reconstruction to the glacier now, determined the volume and hence
mass loss between the Little Ice Age and now.
The Himalayan glaciers are generally losing mass faster in the eastern
regions—taking in east Nepal and Bhutan north of the main divide. The study
suggests this variation is probably due to differences in geographical
features on the two sides of the mountain range and their interaction with
the atmosphere—resulting in different weather patterns.
Himalayan glaciers 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.
Similarly, glaciers which have significant amounts of natural debris upon
their surfaces are also losing mass more quickly: they contributed around
46.5% of total volume loss despite making up only around 7.5% of the total
number of glaciers.
Dr. Carrivick said: "While we must act urgently to reduce and mitigate the
impact of human-made climate change on the glaciers and meltwater-fed
rivers, the modeling 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, said: "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."
The paper "Accelerated mass loss of Himalayan glaciers since the Little Ice
Age" is published in Scientific Reports.
Reference:
Accelerated mass loss of Himalayan glaciers since the Little Ice Age,
Scientific Reports (2021).
DOI: 10.1038/s41598-021-03805-8
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