The catastrophic flash flood that tore through the border communities of Nepal and Tibet has confirmed what scientists have been saying for years: climate change is messing with the very ground beneath our feet, and millions of people are in the firing line.
Satellite imagery points to a glacier collapse high in the Himalayas as the primary culprit behind the deadly torrent of mud, water, and ice that ripped along the Bhotekoshi River on Wednesday. The disaster swept away buildings and roads, leaving at least 360 dead and 1,400 missing.
Initially, a magnitude 4.4 earthquake was blamed for the collapse. But now it's thought the real cause was a massive wall of ice crashing down on the north slope of Langtang Lirung, a 7,000-metre (23,000ft) peak, with an impact that registered a magnitude of 5.2.
"Additional analysis of long-period seismic waves indicates that the seismic energy was instead generated by a glacial collapse and debris flow," the US Geological Survey said, in the geological equivalent of 'we checked, and it's worse than we thought.'
The ice-rock avalanche shoved boulders and debris into the Lhende Khola River, a tributary of the Bhotekoshi. Water levels downstream shot up by between 7 and 9 metres within 30 minutes, according to the International Centre for Integrated Mountain Development, an intergovernmental scientific institution.
Scientists are still untangling the precise mechanics of this Himalayan disaster, but many note that glaciers and permafrost worldwide are being weakened by global heating, the result of burning gas, oil, and coal. The glacier chunk detached amid unusual heat that likely melted the ice binding the splintered bedrock together.
Two days before the collapse, ground temperature hit its highest point in two years, according to Dr Hamish Pritchard, a glaciologist with the British Antarctic Survey, whose team had sensors 6 miles (10km) away.
"These high temperatures would have weakened the snowpack, filled crevasses with water and thawed the bonds between ice and rock that hold these glaciers in place," he told the Science Media Centre.
A series of intense heatwaves has hit the region since early this year, affecting countries worldwide. The monsoon season also played a role, saturating the soil and swelling rivers.
This disaster was foretold. In 2023, the UN's top scientific advisory body warned that previously ice-bound landmasses - from permafrost tundra to mountain glaciers - would become increasingly unstable as temperatures rose.
"Every increment of warming will multiply and intensify future hazards from cryosphere regions," observed the Intergovernmental Panel on Climate Change in its sixth synthesis report. "Floods, landslides and freshwater shortages from glacier retreat and snow loss pose a serious threat to mountain regions across the world."
Average global temperatures are nudging closer to 1.5C above preindustrial levels. Alpine and polar regions are warming even faster because the loss of snow and ice removes the land's thermal insulation.
Dr Richard Waller, a senior lecturer in physical geography at Keele University, explained: "The progressive loss of snow and glacier ice results in the surface being less reflective, so it absorbs more solar energy and heats up. In combination with atmospheric warming, this is leading to the melting of mountain permafrost."
"Think of the high mountains like this as shattered bedrock glued together by ice-filled joints. As the permafrost and the ice-filled joints melt, then there's the potential for these types of catastrophic failure."
The thaw is altering the shape, colour, and solidity of the landscape, creating or expanding glacial meltwater lakes and, in the long term, threatening the origin of many rivers and the drinking supplies of populations downstream. In many parts of Asia, hundreds of millions depend on rivers like the Ganges and the Brahmaputra that descend from the glaciers.
Scientists have high confidence that glacier retreat is caused by human-driven global heating. This has caused glacier collapses from the Alps to the Andes. In the Langtang catchment area in Nepal, glacier loss rates have increased more than fourfold since 1964, a study has shown.
This has contributed to loss of life on multiple occasions. A smaller flood hit the Bhotekoshi River in July 2025, and in 2015, an earthquake-induced avalanche destroyed Langtang village.
As emergency services search for bodies and humanitarian groups mobilise for survivors, others are asking where next. Waller said any high mountain areas with glaciers and permafrost could be vulnerable, including the European Alps, Caucasus, Himalayas, Andes, and beyond.
As glacier weakening accelerates, Pritchard called for greater disaster preparedness: "More avalanches and more floods are inevitable, particularly as lakes grow in front of the retreating glaciers. Early warning systems are urgently needed to protect the people living in these valleys."