This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Human-caused global warming thinned glaciers and thawed mountain permafrost, likely helping to destabilize the Himalayan slope that collapsed last month and unleashed catastrophic flooding across Nepal, according to a report released Thursday. The report by the World Weather Attribution cautioned that climate change was not the sole cause of the Aug. 26 disaster.
A large 2015 Nepal earthquake may have weakened the rock years before the collapse, their analysis found. "This disaster was not an extreme weather event, but the fingerprints of climate change are still clear to see in long-term changes," said Ben Clarke, a climate researcher at Imperial College London who worked on the analysis, in a press statement. More than 1,300 people were killed and over 5,000 remain missing after a massive section of rock and overlying glacier collapsed near Nepal's border with China.
The resulting torrent of water, ice, boulders and sediment swept through communities along the Trishuli River corridor and caused billions of dollars in damage. Climate scientists said that across the Himalayas rising temperatures are causing glaciers to retreat and thawing permanently frozen ground that helps bind fractured mountain rock together. That means climate change can alter not only weather hazards such as heat and heavy rain, but the stability of the mountains themselves—threatening communities concentrated in narrow river valleys below.
The analysis did not determine whether the collapse would have happened without climate change, caused mainly by the release of greenhouse gases when fuels like oil, gas and coal are burned. However, researchers concluded that warming intensified several processes that made the slope less stable over decades. The report found that one of the clearest changes directly linked to climate change was the rising elevation of the freezing threshold.
The report found that warming had pushed the altitude at which ground remains consistently frozen upward by roughly 100 meters (328 feet) per decade. This exposes rock at increasingly high elevations to longer periods above freezing, thawing permafrost and causing cracks within the ice, ultimately weakening the rock face under the ice. Jakob Steiner, a geoscientist at the University of Graz who has worked in the Himalayan region since 2006 but is not an author of Thursday's report, said monitoring instruments around 5,000 meters (16,404 feet) now show that some rock and ground no longer remain frozen throughout the year.
"This means that the ground that was sitting below ice for hundreds and thousands of years is now becoming exposed," said Steiner. The report found that glacier retreat was another destabilizing force. Glaciers in the region have been losing mass for decades at a rate equivalent to more than half a meter (about 1.6 feet) of thinning each year, the report found.
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