Two-thirds of Himalayan glaciers, the world's "Third Pole", could melt by 2100 if global emissions are not reduced, scientists warned in a major new study issued Monday.
And even if the "most ambitious" Paris Agreement goal of limiting global warming to 1.5 degrees Celsius is achieved, one-third of the glaciers would go, according to the Hindu Kush Himalaya Assessment.
Glaciers in the Hindu Kush-Himalaya (HKH) region are a critical water source for some 250 million people in the mountains as well as to 1.65 billion others in the river valleys below, the report said.
The glaciers feed 10 of the world's most important river systems, including the Ganges, Indus, Yellow, Mekong and Irrawaddy, and directly or indirectly supply billions of people with food, energy, clean air and income.
Impacts on people from their melting will range from worsened air pollution to more extreme weather, while lower pre-monsoon river flows will throw urban water systems and food and energy production off-kilter, the study warned.
As the glaciers shrink, hundreds of risky glacial lakes that could burst and unleash floods have formed in the foothills of the mountains, which include giants such as Everest and K2.
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The new report was published by the Kathmandu-based International Centre for Integrated Mountain Development (ICIMOD) in Nepal, one of eight countries on the front line.
Five years in the making, it involved more than 350 researchers and policy experts, 185 organisations, 210 authors, 20 review editors and 125 external reviewers.
"Global warming is on track to transform the frigid, glacier-covered mountain peaks... cutting across eight countries to bare rocks in a little less than a century," Philippus Wester of ICIMOD, who led the report, said in a statement.
"This is the climate crisis you haven't heard of." The region would require up to $4.6 billion per year by 2030 to adapt to climate change, rising to as much as $7.8 billion per year by 2050, according to an estimate in the report.