Warming glaciers and thawing permafrost helped drive deadly Nepal-China flood, scientists say

A report published Thursday by World Weather Attribution says human-caused climate change played a major role in last month’s deadly Himalayan disaster in Nepal. Rising temperatures had thinned glaciers and thawed mountain permafrost, processes that likely weakened the slope before it gave way.

The 26 August collapse near Nepal’s border with China sent water, ice, boulders and sediment surging through communities along the Trishuli River corridor. More than 1,300 people were killed and over 5,000 remain missing.

“This disaster was not an extreme weather event, but the fingerprints of climate change are still clear to see in long-term changes,” said Ben Clarke, a climate researcher at Imperial College London who contributed to the report.

Across the Himalayas, rising temperatures are driving glacier retreat and thawing the permafrost that helps hold fractured mountain rock together. Climate change can therefore affect not only hazards such as extreme heat and heavy rainfall, but also the stability of mountains above communities in narrow river valleys.

The analysis could not determine whether the collapse would have occurred without climate change, which is driven mainly by greenhouse gas emissions from burning fuels such as coal, oil and gas. Researchers concluded, however, that warming intensified several long-term processes that made the slope increasingly unstable.

Warming is destabilising high-mountain slopes

One of the clearest climate-linked changes identified in the report was the rising elevation of the threshold below which ground remains continuously frozen.

According to the analysis, warming has pushed that altitude upward by about 100 metres per decade.

As a result, rock at higher elevations is exposed to above-freezing temperatures for longer periods. Permafrost thaws and cracks develop within the ice, ultimately weakening the rock faces beneath it.

Jakob Steiner, a geoscientist at the University of Graz who has worked in the Himalayas since 2006 but did not contribute to Thursday’s report, said instruments at elevations of around 5,000 metres now show that some rock and ground no longer stay frozen throughout the year.

“This means that the ground that was sitting below ice for hundreds and thousands of years is now becoming exposed,” Steiner said.

The report also identified glacier retreat as another force destabilising the mountainside.

Regional glaciers have been losing mass for decades at a rate equivalent to more than half a metre of thinning each year, the analysis found. The Langtang Lirung glacier, in the region where the disaster occurred, has retreated about half a kilometre since the 1990s, exposing rock once covered by ice.

The Himalayas hold the largest volume of snow and ice outside the polar regions. More than 63,000 glaciers feed at least 10 major Asian river systems and underpin the food, water, energy and livelihood security of billions of people. Studies indicate that around 78% of the region’s glacier area, situated between 14,763 and 19,685 feet above sea level, is highly vulnerable to warming.

United Nations reports have found that glaciers lost an average of 267 billion tonnes of ice each year between 2000 and 2019—roughly equivalent to the mass of 46,500 Great Pyramids of Giza.

As glaciers shrink, they can withdraw support once provided to neighbouring rock walls while also generating more meltwater.

The analysis found that conditions in the weeks before the 26 August collapse were also unusually warm. July and August 2026 were the warmest such months recorded in the area.

“Other than the potential geological factors like earthquakes that are weakening the bedrock, all these other factors are made worse by human-induced climate change,” said Friederike Otto, a climate scientist at Imperial College London and one of the report’s authors.

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