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Climate attribution researchers say “there is absolutely no doubt” that decades of global warming set the stage for the deadly rock and glacier collapse on Langtang Lirung Mountain in Nepal, Inside Climate News reports.
At least 1,300 people died in August when a cascade of semi-frozen sludge, boulders, trees, and other debris roared through the region at speeds up to 100 mph and crested up to 300 feet high, Inside Climate writes. The disaster destroyed and damaged towns, farms, orchards, roads, bridges, and energy infrastructure, devastating livelihoods across the region. The total losses are now estimated at about US$5 billion.
In a new analysis of the Aug. 26 disaster, a team of scientists with World Weather Attribution highlighted that record-hot temperatures baked the region in the months before the disaster. That was preceded by unusually high snowfall in late 2025, which is usually a very dry time for the region. Additional meltwater from the snow was probably another element in a complex chain of climate-linked factors contributing to the disaster, said Walter Immerzeel, a co-author of the new analysis.
Warming has hollowed out ancient ice and thawed the permafrost, the frozen ground that helps bind high mountain slopes together, leaving them increasingly vulnerable to collapse.
According to new estimates, about 116 million cubic metres of rock and ice initially broke away from the face of the mountain, the equivalent of a 96-square-block area of Manhattan breaking off all at once and plunging several thousand vertical feet within minutes. The size of the initial disintegration is unprecedented in the Himalayas, said Immerzeel, a mountain hydrologist at Utrecht University in the Netherlands who spent years researching in the region affected by the recent catastrophe.
The volume is about five times that of the most comparable mountain collapse and flood in the region, the 2021 Chamoli disaster in Uttarakhand, India. The increasing frequency and scale of mountain and glacier collapses and subsequent floods are signs of “fundamental, irreversible shifts in Himalayan mountain environments,” Immerzeel said.
Nepal has sought aid from the international fund for climate losses and damage set up through the United Nations climate framework. But the fund only has about $800 million pledged, with roughly $350 million available for claims, a fraction of the estimated damage from this single disaster.
The flood first swept through the upper Lhende valley and the settlements of Rasuwa district, including Rasuwagadhi and Timure, before surging through the Bhote Koshi and Trishuli river systems, about 100 miles downstream. About 5,000 people are still missing.
Immerzeel said the new analysis highlights the changes in background conditions that affect hazards for people and resources. That may be more consequential than identifying the exact trigger for a single specific event, several co-authors said during a media briefing on the new analysis.
Immerzeel said climate change from burning fossil fuels is pushing the freezing line upward by roughly 100 metres per decade, heating bedrock that has been frozen in place for thousands of years and spreading that heat beneath the glaciers.
Some of the melting ice has been frozen for tens of thousands of years. Warm meltwater flows deep into cracks in the rocks, exerting enormous hydraulic pressure. Then it refreezes in winter, widening the fissures; when it melts again in spring, gravity takes hold.
“When you combine high-elevation permafrost degradation with glacier retreat and record summer heat, the structural integrity of these mountain walls is compromised,” Immerzeel said. “The catastrophic impacts of what can then happen are clear for all to see.”
Co-author Prof. Friederike Otto, professor of climate science at the Centre for Environmental Policy, Imperial College London, said the analysis shows how permafrost thawing, glacier thinning, and more rain instead of snow had the effect of “preconditioning” the mountain for collapse.
She said scientists could be even more specific about how much human-caused warming contributed to the disaster with more detailed glacier modelling and readings from nearby glaciers. But that shouldn’t matter in the context of funding to cover the cost of climate impacts, she added, addressing the question of who should help Nepal pay for a climate disaster caused by billions of tonnes of carbon dioxide emissions from rich, developed countries.
Co-author Madhab Uprety, a technical expert with the Red Cross Red Crescent Climate Centre, said the extreme flood challenged basic assumptions about what communities in the region must prepare for.
