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

Climate change played a significant role in a deadly Himalayan disaster that occurred last month near the border between Nepal and China, according to a report released on Thursday by the World Weather Attribution group. Researchers stated that the tragedy was driven by a compound crisis involving long-term warming, glacier retreat, permafrost thaw, and geological instability, with a 2015 earthquake also thought to have contributed.

The slope collapse took place on August 26, unleashing a massive torrent of water, ice, boulders, and sediment through communities along the Trishuli River corridor. The resulting disaster caused the deaths of more than 1,300 people and left over 5,000 missing, prompting subsequent rescue efforts, hydropower tunnel extractions, mass burials for unidentified victims, and a national day of mourning in Nepal.

Ben Clarke, a climate researcher at Imperial College London who contributed to the report, noted that while the disaster was not an extreme weather event, the fingerprints of climate change remain clear in the long-term shifts observed in the region. Scientists explained that rising temperatures across the Himalayas are causing glaciers to retreat and permanently thawing ground that traditionally binds fractured mountain rock together. Consequently, climate change alters not only weather hazards like heat and heavy rain, but also the stability of the mountains themselves, endangering populations living in narrow river valleys below.

Although the analysis did not explicitly determine whether the collapse would have occurred in the absence of climate change—which is primarily driven by greenhouse gas emissions from burning fossil fuels like coal, oil, and gas—researchers concluded that warming intensified several underlying processes that progressively destabilized the slope over decades.

The report highlighted that one of the most distinct changes directly linked to global warming is the rising elevation of the freezing threshold. According to the findings, warming has pushed the altitude at which ground remains consistently frozen upward by roughly 100 meters per decade. This exposes rock at higher elevations to extended periods above freezing, thawing permafrost and causing ice cracks that ultimately weaken the rock face.

Jakob Steiner, a geoscientist at the University of Graz who has worked in the Himalayan region since 2006 but did not author the Thursday report, observed that monitoring instruments positioned around 5,000 meters now indicate some rock and ground no longer remain frozen throughout the entire year. Steiner noted that ground sitting beneath ice for hundreds and thousands of years is now becoming exposed.

Furthermore, the report identified glacial retreat as an additional destabilizing force. Regional glaciers have lost mass for decades at a rate equivalent to more than half a meter of thinning annually. Specifically, the Langtang Lirung glacier in the disaster zone has retreated roughly half a kilometer since the 1990s, exposing rock previously covered by ice. As glaciers shrink, they can eliminate pressure that previously helped support adjoining rock walls while simultaneously generating extra meltwater.

The Himalayan region houses the largest volume of snow and ice outside the polar regions, with more than 63,000 glaciers feeding at least 10 major Asian river systems and supporting food, water, energy, and livelihood security for billions of people. Studies indicate that approximately 78% of this glacier area, located between 14,763 and 19,685 feet above sea level, is highly vulnerable to warming. Furthermore, United Nations reports show that between 2000 and 2019, glaciers lost 267 billion tonnes of ice annually.

The analysis also pointed out that the weeks preceding the August 26 collapse were exceptionally warm, with July and August 2026 marking the warmest such months recorded locally. Friederike Otto, a climate scientist at Imperial College London and one of the report's authors, stated that apart from potential geological factors like earthquakes weakening the bedrock, all other contributing factors are worsened by human-induced climate change.