Climate change was key factor in deadly Nepal-China flood, scientists say

Researchers said the flood was caused by a "compound crisis" shaped by long-term warming, glacier retreat, permafrost thaw and geological instability. A 2015 earthquake is also thought to have played a role. Climate change played a significant role in last month's deadly Himalayan disaster in Nepal, thinning glaciers and thawing mountain permafrost in ways that likely destabilised the slope before it collapsed, a report released Thursday by the World Weather Attribution group said. The collapse, near Nepal's border with China on 26 August, triggered a torrent of water, ice, boulders and sediment that swept through communities along the Trishuli River corridor, killing more than 1,300 people and leaving over 5,000 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. Climate scientists said that across the Himalayas rising temperatures are causing glaciers to retreat and permanently thawing ground that helps bind fractured mountain rock together. That means climate change can alter not only weather hazards such as heat and heavy rain but also the stability of the mountains themselves — threatening communities concentrated in narrow river valleys below. The analysis did not determine whether the collapse would have happened without climate change, caused mainly by the release of greenhouse gases when fuels like oil, gas and coal are burnt. However, researchers concluded that warming intensified several processes that made the slope less stable over decades. Global warming weakens high mountain slopes The report found that one of the clearest changes directly linked to climate change was the rising elevation of the freezing threshold. Warming had pushed the altitude at which ground remains consistently frozen upward by roughly 100 metres per decade, according to the report. This exposes rock at increasingly high elevations to longer periods above freezing, thawing permafrost and causing cracks within the ice, ultimately weakening the rock face under the ice. Jakob Steiner, a geoscientist at the University of Graz who has worked in the Himalayan region since 2006 but is not an author of Thursday’s report, said monitoring instruments around 5,000 metres now show that some rock and ground no longer remain frozen throughout the year. “This means that the ground that was sitting below ice for hundreds and thousands of years is now becoming exposed,” said Steiner. The report also found that glacial retreat was another destabilising force. Glaciers in the region have been losing mass for decades at a rate equivalent to more than half a metre of thinning each year, the report found. The Langtang Lirung glacier, located in the region where the disaster occurred last month, has retreated about half a kilometre since the 1990s, exposing rock once covered by ice. The Himalayan region contains the largest volume of snow and ice outside the polar regions. More than 63,000 glaciers in the area feed at least 10 major Asian river systems and support the food, water, energy and livelihood security of billions of people. However, various studies have found that around 78% of the glacier area, located between 14,763 and 19,685 feet above sea level, is highly exposed to warming. United Nations reports have found that between 2000 and 2019, glaciers lost 267 billion tonnes of ice per year, roughly equivalent to the mass of 46,500 Great Pyramids of Giza. As glaciers shrink, they can remove pressure that helped support adjoining rock walls while producing additional meltwater. According to the analysis, the weeks before the 26 August collapse were also unusually warm. July and August 2026 were the warmest such months recorded locally. “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, climate scientist at Imperial College London and one of the report’s authors.