Nepal glacier collapse made more likely by warming, report finds

Human-caused climate change thinned glaciers and thawed mountain permafrost, making the collapse of a Himalayan slope last month and the catastrophic flooding that followed more likely, according to a report released Thursday. The analysis cautioned that climate change was not the sole cause of the Aug. 26 disaster.

A large 2015 Nepal earthquake may have weakened the rock years before the collapse, the report by World Weather Attribution found.

“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 worked on the analysis, in a press statement.

More than 1,300 people were killed and over 5,000 remain missing after a massive section of rock and overlying glacier collapsed near Nepal’s border with China. The resulting torrent of water, ice, boulders and sediment swept through communities along the Trishuli River corridor and caused billions of dollars in damage.

The report found that warming had pushed the altitude at which ground remains consistently frozen upward by roughly 100 meters (328 feet) per decade. 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.

Glaciers in the region have been losing mass for decades at a rate equivalent to more than half a meter (about 1.6 feet) 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 kilometer (0.3 miles) since the 1990s, exposing rock once covered by 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 the report, said monitoring instruments around 5,000 meters (16,404 feet) 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 weeks before the Aug. 26 collapse were also unusually warm. July and August 2026 were the warmest such months recorded locally, according to the analysis.

“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.

The analysis did not determine whether the collapse would have happened without climate change. However, researchers concluded that warming intensified several processes that made the slope less stable over decades.

The report said the catastrophe also demonstrates how some climate-related risks in the world’s highest mountains may exceed the protection that early warning systems and other adaptation measures can provide. Nepal has developed disaster risk reduction plans and warning systems, but researchers said the size and speed of the collapse overwhelmed those defenses.

“Small changes in temperatures affect the stability of the land itself,” Otto said.

Since glaciers and permafrost respond to temperature changes over decades, some mountain destabilization caused by warming has already been set in motion, the report said.

“The most important thing to minimize the risk in this region is to rapidly stop using fossil fuels that lead to increasing global temperatures,” said Otto. “All these drivers that we’ve talked about, permafrost melting, glacial melting, etc., will just become worse. And that means that events like this become more frequent.”