As global temperatures heat up, one-third of glaciers in the Hindu Kush Himalayan region are slated to disappear by the end of the century, according to a report published on Monday.

The mountain system spans more than 2,000 miles between Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal, and Pakistan. The glaciers supply water to 250 million people, and feed into rivers that support 1.65 billion citizens of nearby countries. Their disappearance would have fatal consequences for already vulnerable populations.

“This is the climate crisis you haven’t heard of,” Philippus Wester, chief scientist at the International Centre for Integrated Mountain Development and co-author of the report, said in a statement on Monday.

Source: International Centre for Integrated Mountain Development

The new assessment is grim, stating that 36 percent of region’s glaciers will melt by 2100 even if warming is kept to 1.5 degrees Celsius above pre-industrial levels. This is the most realistic emissions goal set by the Paris Agreement, which still requires “rapid and far-reaching” societal changes, according to climate scientists.

If global temperatures rise 2 degrees Celsius, that percentage would jump to half. A temperature increase of 4 to 5 degrees Celsius would see the disappearance of two-thirds of the region’s glaciers.

Monday’s report is “one of the most complete studies on mountain warming,” according to the New York Times. It represents five years of work by 200 scientists, and was commissioned by the eight countries who comprise the mountainous region.

Roughly 15 percent of the region’s ice cover has vanished since the 1970s, the report noted.

A phenomenon called elevation-dependent warming means the mountains of the Hindu Kush Himalayan region are warming at an accelerated rate, though it’s unclear precisely why, the report noted.

Monday’s report also underscores recent findings by the Intergovernmental Panel on Climate Change that global warming will disproportionately harm poor countries.

The cascading effects of climate change include impacts to human health, agriculture, tourism, social conflict, and the “forced environmental migration” of populations due to labor or resource shortages.

Near Mount Everest in Nepal, which is part of the Hindu Kush Himalayan region, deadly flooding from glacial melt already threatens downslope communities.

Drought is one of the biggest looming threats across Asia. Last year, residents in the Indian city of Shimala, nestled in the Himalayas, asked tourists to stay away to preserve water. In Pakistan, where many rivers are fed by glaciers, a lack of water influenced its ranking among the top ten countries most affected by climate change, per the 2018 Global Climate Risk Index.

“Mountain people are really getting hit hard,” David Molden, director general of the International Center for Integrated Mountain Development in Nepal and leader of the study, told the New York Times on Monday. “We have to do something now.”

An estimated 50,000 glaciers in the the Hindu Kush Himalayan region are the source of 10 Asian river systems, justifying its nickname as the “water tower” of Asia. The region has also been called the “third pole” for packing the most ice and snow outside of the North and South poles.