Climate change helped set the stage for last month’s catastrophic rock-and-ice collapse on Nepal’s northern border, researchers say, by thinning glaciers and thawing the frozen ground that had long acted as a natural cement holding the mountain together.
In an assessment led by World Weather Attribution scientists working with international glaciologists, the team found no evidence that a single extreme weather event directly triggered the failure.
Instead, they concluded the collapse was the outcome of a gradual buildup of climatic and geological pressures that steadily undermined the stability of the mountainside.
Human-caused warming driven by the burning of fossil fuels has lifted the freezing threshold in the high Himalayas by about 100 metres per decade.
An assessment by World Weather Attribution scientists found the disaster was not triggered by a single extreme weather event
That shift means rock and permafrost that once remained locked in ice for most of the year are now exposed to warmer temperatures for longer stretches.
Alongside this, major glacier thinning and retreat have stripped away ice that previously buttressed and stabilised the slope.
Scientists said these long-term trends — together with other influences that may include lingering destabilisation from the magnitude 7.8 earthquake that struck Nepal in 2015 — likely weakened the mountainside over time, leaving it increasingly prone to collapse.
The two months leading up to the disaster were the warmest July and August ever recorded in the area.
Researchers also noted that exceptionally heavy snowfall in October and November last year could have contributed by supplying large volumes of meltwater in the months before the collapse.
According to the scientists, warming has driven substantial glacier recession around the failure site, removing stabilising ice while also increasing the amount of meltwater available.
But they said one of the most consequential long-term shifts is happening inside the mountain itself, as rock, soil and sediment that have remained frozen for centuries begin to thaw.
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As that frozen ground softens, water can seep deeper into fractures, widening cracks and weakening slopes that were previously reinforced by ice.
The report characterises the incident as a “compound crisis”, with several processes acting together rather than one identifiable weather event setting off the collapse.
“While the underlying geological structure controlled where and how the slope failed, longer-term warming and changing precipitation phase from snow to rain may have reduced its stability by weakening ice-filled fractures and rock–ice contacts and increasing water pressure,” the scientists concluded.
“Climate change is thus best understood as a destabilising factor acting on a pre-existing geological predisposition, rather than the fundamental cause of the failure.”
The team said they are particularly concerned that some effects of warming already recorded in the Himalayas will continue to play out for decades.
Glaciers and high-altitude permafrost, they noted, respond slowly to temperature shifts.
That lag means warming that has already occurred has effectively locked in further glacier loss and a continuing risk of unstable mountain slopes.
The scientists said the most effective way to limit future destabilisation is to curb additional warming through rapid cuts in greenhouse gas emissions and the phase-out of fossil fuels.
