The report from the Kathmandu-based International Centre for Integrated Mountain Development (ICIMOD) on Tuesday warned that flash floods and avalanches would grow more likely in coming years and that the availability of fresh water would be affected for the 240 million people who live in the region as well as a further 1.65 billion downstream.

“The people living in these mountains who have contributed next to nothing to global warming are at high risk due to climate change,” said Amina Maharjan, a migration specialist and one of the report’s authors.

“Current adaptation efforts are wholly insufficient and we are extremely concerned that without greater support, these communities will be unable to cope,” she said.

Various earlier reports have found that the cryosphere – regions on Earth covered by snow and ice – are among the worst affected by climate change.

Recent research found that Mount Everest’s glaciers, for example, have lost 2,000 years of ice in just the past 30 years.

“We map out for the first time the linkages between cryosphere change with water, ecosystems and society in this mountain region,” Maharjan said.

The report found that the Himalayan glaciers disappeared 65 percent faster since 2010 than in the previous decade and said that changes to the glaciers, snow and permafrost of the region driven by global warming were “unprecedented and largely irreversible”.

At 1.5 degrees Celsius or 2 degrees Celsius of warming above preindustrial temperatures, glaciers across the entire region will lose 30 percent to 50 percent of their volume by 2100, it said.

But where glaciers will melt most depends on location. At 3 degrees Celsius of warming – what the world is roughly on track for under current climate policies – glaciers in the Eastern Himalayas, which includes Nepal and Bhutan, will lose up to 75 percent of their ice. At 4 degrees Celsius of warming, that increases to 80 percent.

“We’re losing the glaciers, and we’re losing them in 100 years time,” said Philippus Wester, an environmental scientist and ICIMOD fellow who was the lead author of the report.

The full picture

The Hindu Kush Himalaya stretches 3,500 km (2,175 miles) across Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal and Pakistan.

Scientists have struggled to assess how climate change is affecting the Hindu Kush Himalaya. Unlike the European Alps and North America’s Rocky Mountains, the region lacks a long historical record of field measurements that reveal whether glaciers are growing or shrinking.

“There was always some uncertainty in the Himalayas – are they really melting?”, said Wester.

In 2019, the United States declassified spy satellite images of the region’s glaciers dating back to 1970, providing a new scientific baseline.

Further advances in satellite technology in the past five years, alongside stepped-up field research, have boosted scientists’ understanding of the changes under way. The report draws on data until December 2022.

Compared with a 2019 ICIMOD assessment of the region, “there’s a much higher level of confidence now in these findings”, said Wester.

“We have a better sense of what the loss will be through to 2100 at different levels of global warming.”

With this newfound understanding comes grave concern for the people living in the Hindu Kush Himalaya.

The report found water flows in the region’s 12 river basins, including the Ganges, Indus and Mekong, are likely to peak around the mid-century, with consequences for the more than 1.65 billion people who depend on this supply.

“While it may sound like we’ll have more water because glaciers are melting at an increased rate … too frequently it will arise as floods instead of a steady flow,” said Wester.

The study said that 200 glacier lakes across these mountains are deemed dangerous and the region could see a significant spike in glacial lake outburst floods by the end of the century.

But once past peak water, supplies will eventually dwindle.

“Once ice melts in these regions, it’s very difficult to put it back to its frozen form,” said Pam Pearson, director of the International Cryosphere Climate Initiative, who was not involved with the report.

She added: “It’s like a big ship in the ocean. Once the ice starts going, it’s very hard to stop. So, with glaciers, especially the big glaciers in the Himalayas, once they start losing mass, that’s going to continue for a really long time before it can stabilise.”

Pearson said it is extremely important for Earth’s snow, permafrost and ice to limit warming to the 1.5 degrees Celsius agreed to at the 2015 Paris climate conference.

“I get the sense that most policymakers don’t take the goal seriously but, in the cryosphere, irreversible changes are already happening,” she said.

The effects of climate change are already felt by Himalayan communities, sometimes acutely.

Earlier this year the Indian mountain town of Joshimath began sinking and residents had to be relocated within days.

Governments in the region are trying to prepare for these changes. China is working to shore up the country’s water supplies. And Pakistan is installing early warning systems for glacial lake outburst floods.