Climate change likely to have helped trigger Nepal glacier collapse, scientists say

Rapidly warming temperatures in the region have caused glaciers to thin and have melted ice and permafrost buried deep in the bedrock of the Himalayas, according to the World Weather Attribution (WWA) group of researchers. 

While it is difficult to ascertain the precise role played by climate change in the collapse of around 2 sq km (0.8 sq miles) of rock wall and glacier ice on the Langtang Lirung mountain last month, soaring temperatures created the preconditions that made it more likely, researchers involved in the study said.

"There's absolutely no doubt that human induced climate change played a role here in the preconditioning of the disaster through permafrost thawing, through thinning of the glaciers, through having more rainfall instead of snow," said Friederike Otto, a climatologist at Imperial College London.

WWA uses peer-reviewed methods to assess the role played by global warming in extreme weather events, according to its website. 

The study said mean temperatures were around 5 degrees Celsius (9 degrees Fahrenheit) higher than normal in the Himalayan region in August, with 1.5 C of the increase coming from climate change. 

Unusually high levels of snowfall in October and November of last year also added to the volume of meltwater once temperatures began to rise, which could have helped trigger the glacier collapse, according to the study. 

Glaciers in the region have been thinning by about half a metre per year (about 1.6 feet) since the year 2000, changing stresses on the rock. Melting permafrost is also likely to have weakened the rock wall, the study said. 

A 7.8 magnitude earthquake that hit the same mountain in 2015 could have played a role by weakening the underlying bedrock as well, but its precise impact is unclear.

"We conclude that this was a geologically vulnerable slope, potentially weakened by the 2015 earthquake, but it was destabilised further by glacier and permafrost retreat and by the excessive meltwater and exceptional warmth in the final period before the collapse," said Walter Immerzeel, a mountain hydrologist from Utrecht University.