Kathmandu: Human caused climate change likely helped destabilise the mountain slope involved in the catastrophic collapse that triggered deadly flooding in Nepal last month, according to a new scientific assessment. Researchers say rising temperatures have contributed to glacier loss, thawing permafrost and changes in rainfall and snowfall, creating conditions that can make high mountain slopes less stable.
The disaster occurred on August 26 when a large section of rock and glacier ice collapsed from Langtang Lirung mountain in northern Nepal. The collapse sent huge amounts of rock and ice down the mountain, triggering a debris flood that later developed into a powerful flash flood downstream.
The World Weather Attribution group said climate change was an important factor in the long term weakening of the mountain environment. However, researchers stressed that warming was not the only factor and that they could not establish whether this particular collapse would have happened without human caused climate change.
The assessment found unusually warm conditions in the Himalayan region during July and August. Researchers estimated that human caused climate change contributed about 1.5 degrees Celsius to temperatures during those two months.
Rising temperatures have changed the high altitude environment in several ways. Glaciers in the region have been losing mass at a rate equivalent to more than half a metre of thinning each year since 2000. The Langtang Lirung glacier has also retreated by about half a kilometre since the 1990s.
As glaciers retreat, rock that was previously covered and supported by ice becomes exposed. At the same time, warming can thaw permafrost, which is ground that has remained frozen for long periods. Ice inside cracks in mountain rock can help hold the rock together. When that ice melts, the slope can become weaker.
The 0 degree Celsius freezing threshold has also been moving upward by about 100 metres per decade in recent decades during the monsoon and post monsoon seasons. This means that increasingly high parts of the Himalayas are being exposed to temperatures above freezing.
Changing precipitation is another factor. More precipitation at high elevations is falling as rain rather than snow. Rain can enter cracks in rock and increase water pressure, while snow can remain stored on the mountain for longer periods.
Researchers also identified unusually high snowfall in October and November 2025. The additional snow later produced more meltwater as temperatures increased. Scientists said this may have contributed to the conditions before the collapse, although its precise role has not been established.
The mountain was already considered geologically vulnerable. Researchers said the magnitude 7.8 earthquake that struck Nepal in 2015 may have weakened the underlying rock. The exact contribution of that earthquake to the 2026 collapse remains unclear.
The United States Geological Survey later determined that the seismic signal recorded during the disaster was generated by the collapse and debris flow, rather than by a separate earthquake triggering the event.
The collapse began at an elevation of about 5,150 metres on Langtang Lirung. The resulting avalanche moved into the river system and affected areas far downstream, including communities and infrastructure around Rasuwa district and the Rasuwagadhi border area with China.
The disaster caused a major loss of life and widespread destruction. Nepalese authorities have reported more than 1,400 deaths, while thousands of people remain missing. The figures continue to change as search, recovery and identification operations proceed.
The continuing uncertainty over the number of missing people is partly linked to the difficulty of identifying recovered bodies and reconciling different records of people who were missing after the disaster.
The flooding also damaged roads, bridges, hydropower facilities and other infrastructure. Nepal has estimated that billions of dollars will be required for recovery and reconstruction following the disaster.
The United Nations has also appealed for international support for people affected by the floods and related destruction. The disaster has placed additional pressure on communities already facing the effects of changing weather and environmental conditions in the Himalayas.
The new scientific assessment has broader implications for communities living in high mountain regions. Researchers say warming is changing not only glaciers and snow but also the stability of mountain slopes.
The researchers said the event was beyond the design and predictive limits of existing risk reduction measures, highlighting the difficulty of protecting communities from sudden disasters that begin with high altitude rock and ice collapses.
Better monitoring of glaciers, unstable slopes and permafrost, together with improved early warning systems, could help reduce some risks. But scientists also stress that many changes caused by long term warming are already taking place across the Himalayas.
For Nepal, the disaster has also increased calls for international action on climate related losses and adaptation. The government has said it plans to raise issues including climate finance and loss and damage at the United Nations.
The latest scientific assessment does not present the August disaster as a simple case of climate change causing a glacier collapse. Instead, it shows how long term warming can interact with geological weaknesses, glacier retreat, thawing permafrost and changing water conditions to increase the danger of sudden mountain disasters.
For communities living along the narrow valleys of the Himalayas, understanding and monitoring these changing risks is becoming an increasingly important challenge.