Climate change led to Nepal landslide, scientists find

Climate change contributed to the conditions that led to last month's catastrophic rock and ice collapse on Nepal’s northern border by thinning glaciers and thawing the frozen ground that helped hold the mountain together, scientists have concluded.

An assessment by World Weather Attribution scientists and international glaciologists found the disaster was not triggered by a single extreme weather event.

Instead, they concluded it resulted from a combination of climatic and geological factors that had progressively destabilised the mountainside.

Human-caused warming from the burning of fossil fuels has pushed the freezing threshold in the high Himalayas upwards by around 100 metres per decade.

This has caused previously frozen rock and permafrost to be exposed to warmer temperatures for longer periods of time.

At the same time, substantial glacier thinning and retreat has removed ice that previously helped support and stabilise the mountain slope.

The scientists believe these long-term changes, as well as other factors potentially including destabilisation caused by the magnitude 7.8 earthquake which struck Nepal in 2015, all weakened the mountainside, leaving it increasingly vulnerable to collapse.

The two months immediately before the disaster were the warmest July and August on record in the area.

Exceptionally heavy snowfall during October and November last year may also have played a role by providing large quantities of meltwater during the months preceding the collapse.

The scientists said warming has caused substantial glacier recession around the failure site, removing stabilising ice while also increasing the availability of meltwater.

But one of the most significant long-term changes is occurring within the mountain itself as the rock, soil and sediment that have been frozen for centuries are thawing.

This allows water to penetrate cracks and weaken slopes which had previously been held together by ice.

Today’s report describes the disaster as a "compound crisis" in which several processes acted together rather than one identifiable weather event causing the collapse.

Scientists are particularly concerned that some of the consequences of warming already experienced in the Himalayas will continue to unfold for decades.

Glaciers and high-altitude permafrost respond slowly to changes in temperature.

As a result, warming that has already occurred has effectively locked in further glacier loss and destabilisation of mountain slopes.

The scientists said limiting further warming through rapid reductions in greenhouse gas emissions and the phase-out of fossil fuels remains critical to reducing the extent of future destabilisation.