Human-caused global warming significantly contributed to the catastrophic collapse of a Himalayan glacier and rock face in Nepal last month, according to a report released Thursday by the World Weather Attribution group. The analysis found that rising temperatures had thinned glaciers and thawed mountain permafrost over decades, likely destabilising the slope that gave way on 26 August near Nepal's border with China. The resulting torrent of water, ice, boulders and sediment swept through communities along the Trishuli River corridor, killing more than 1,300 people and leaving over 5,000 missing, while causing billions of dollars in damage.

Researchers were careful to note that climate change was not the sole cause. A major earthquake that struck Nepal in 2015 may have weakened the underlying bedrock years before the collapse. "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. The analysis did not establish whether the collapse would have occurred without climate change — driven mainly by greenhouse gas emissions from burning oil, gas and coal — but concluded that warming had intensified several processes that made the slope progressively less stable.

Among the most significant findings was that warming has pushed the altitude at which ground remains consistently frozen upward by roughly 100 metres per decade. This thaws permafrost that once helped bind fractured mountain rock together, creating cracks and weakening slopes at increasingly high elevations. Jakob Steiner, a geoscientist at the University of Graz who has worked in the Himalayan region since 2006, noted that monitoring instruments at around 5,000 metres now show that some rock and ground no longer stay frozen year-round. "This means that the ground that was sitting below ice for hundreds and thousands of years is now becoming exposed," he said. Separately, the Langtang Lirung glacier near the disaster site has retreated about half a kilometre since the 1990s, exposing rock that was once supported and insulated by ice. The weeks before the collapse were also the warmest July and August on record locally.

The Himalayan region, which contains the largest volume of snow and ice outside the polar regions, is of critical global importance. More than 63,000 glaciers there feed at least ten major Asian river systems and underpin the water, food and energy security of billions of people. United Nations data show that between 2000 and 2019, Himalayan glaciers lost roughly 267 billion tonnes of ice per year — equivalent in mass to about 46,500 Great Pyramids of Giza.

The disaster also exposed the limits of adaptation in high mountain environments. Nepal has developed early warning systems and disaster risk reduction plans, but the sheer speed and scale of the collapse overwhelmed those defences. Unlike rainfall-driven floods, which can sometimes be forecast hours in advance, sudden slope failures in remote mountain terrain remain extremely difficult to predict. "Small changes in temperatures affect the stability of the land itself," said Friederike Otto, a climate scientist at Imperial College London and one of the report's authors. She warned that permafrost and glacier loss will continue to worsen unless fossil fuel use is rapidly curtailed, making events like this one more frequent in the decades ahead.