A view of Ama Dablam in eastern Nepal. Photo: Ben Lowe/Unsplash
- In a new study, researchers analysed ice loss from 14,798 Himalayan glaciers since the Little Ice Age, 400-700 years ago.
- They found that the rate of loss in the last few decades has been 10x higher than it was for seven centuries before that.
- Rivers that feed millions of people in South Asia originate from these glaciers, and their affect the monsoons over India as well.
Kochi: We have known for some time that glaciers in the Himalaya are melting and that climate change has been hastening this process.
But now, a new study has found that we are losing these glaciers far faster than ever before. Over the last few decades alone – a time in which anthropogenic global warming has intensified – the rate of ice loss in the Himalaya has accelerated by more than 10x since the Little Ice Age, the last major period of glacier expansion 400-700 years ago.
Meltwater from Himalayan glaciers is important to millions of people in South Asia, including India, but rapid melting is more detrimental than beneficial. The loss is also expected to change weather patterns and even affect the monsoons.
The Himalayan mountains straddle five countries and contain more than 32,000 glaciers. The range also harbours the world’s third-largest amount of glacier ice, after Antarctica and the Arctic, and is why it’s called the ‘third pole’. According to one estimate, these glaciers cover around 35,000 sq. km and contain about 600 billion tonnes of ice – around the total mass of all humans on Earth.
Scientists from the University of Leeds in the UK and other institutes studied changes to 14,798 Himalayan glaciers since the Little Ice Age, and found something worrying. The rate of ice loss from the Little Ice Age to 1975 was 10x lower than the rate of ice loss from 1975 to now.
Put another way, the rate of loss in the last few decades has been 10x higher than it was for seven centuries before that.
They also quantified this devastation in area and volume. The glaciers have shrunk from 28,000 sq. km to some 19,600 sq. km today, a 40% decline. And they have lost 390-586 cu. km of ice in this period. This in turn could have raised sea levels by 0.92-1.38 mm, the study estimated.
Comparisons with glacier loss in other mountains around the world indicated that this rate of loss represents “the most dramatic glacier response of any world region,” the researchers wrote in their study’s paper, published on December 20.
The team also found that the loss of glacial mass is faster in the eastern Himalaya – in parts of eastern Nepal and Bhutan – possibly due to differences in the geographical features between the southern and the northern sides of the mountain range. This could result in dissimilar interactions with the atmosphere, which in turn result in dissimilar weather patterns causing different rates of loss.
They also found that those glaciers that end in lakes are shrinking faster. Lakes can have several warming effects on glaciers. For example, they can cause more underground ice melt, as opposed to melting of just surface ice when the glaciers don’t terminate in lakes.
As previous studies have found, glaciers that have a significant amount of natural debris on their surfaces are also losing mass more quickly. (Such debris can absorb more heat and warm the surrounding ice faster, for example.) Debris-laden glaciers make up only 7.5% of all glaciers but accounted for around 46% of total volume loss, the study found.
“This acceleration in the rate of loss has only emerged within the last few decades, and coincides with human-induced climate change,” Jonathan Carrivick, a coauthor of the paper and deputy head of the University of Leeds School of Geography, said in a press release.
Recent glacial loss
The study also confirms what previous studies have shown: that Himalayan glaciers have retreated in recent years and that climate change is to blame (apart from lakes and debris).
For example, a June 2019 study analysed satellite images of glaciers across India, China, Nepal and Bhutan over 40 years, and found they have been losing more than a foot and a half of ice each year in height since 2000. This was double the amount of melting that happened from 1975 to 2000.
The area under snow cover in the Indian Himalaya has been declining as well. For example, a report by the State Centre on Climate Change, Shimla, and ISRO’s Space Application Centre, Ahmedabad, found that the area under snow cover in the state had declined by 18.5% between 2019-2020 and 2020-2021.
Another study found that both climate change and tectonics could have caused an unnamed 5-km-long glacier in the upper Kali Ganga valley in Uttarakhand’s Pithoragarh to abruptly change its course and merge with an adjacent glacier.
Himalayan glaciers melting faster is an obvious cause for concern. Most of South Asia’s major rivers – including the Brahmaputra, the Ganga and the Indus – originate from Himalayan glaciers, and accelerated glacial melt could affect stable waterflow in these rivers.
If a glacier is melting faster today, in future there will be less and less of it left to feed a river, Wouter Buytaert, a hydrologist at Imperial College, London, wrote in a post. “This means water levels in the rivers they feed will be lower and more variable during dry periods.” And this will, in turn, affect the water security of the millions who depend on these rivers for livelihood, food and energy.
Right now, it is not clear what the climatic response to reduced Himalayan snow cover at this rate could be, Roxy Koll Mathew, a climate scientist at the Indian Institute of Tropical Meteorology, Pune, told The Wire Science. “However, there is a high chance that this has an impact on downstream flow and also on the monsoon,” he wrote in an email.
Arun Bhakta Shrestha, a senior scientist at the International Centre for Integrated Mountain Development, Nepal, compared the Himalaya to a “heat pump” in an interview to The Wire Science in 2018. The mountains heat up so much that they suck moisture from the ocean and bring it to the land – like a pump. This, Shrestha said, gives rise to the monsoons.
“The whole monsoon system exists because of the mountains,” he had said.