Mount Everest’s Khumbu Glacier is the highest glacier in the world, a monumentally slow-moving river of ice that stretches thousands of feet along the mountain’s western face. But as Earth continues to warm, the Khumbu is melting faster than ever, forming lakes as long as several football fields. By the end of the century, it could be one of thousands of Himalayan glaciers that have completely melted away.

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“These glaciers are changing. They’re changing very rapidly .. and our best evidence supports the fact that it’s climatically driven,” Duncan Quincey, a professor of geomorphology at the University of Leeds, tells Sarah Kaplan for the Washington Post.

As world leaders and climate experts prepared for the Paris climate summit this week, Quincey and his colleagues analyzed data gathered from a recent investigation of the lakes forming on the Khumbu Glacier’s surface. While several small ponds have formed on the Khumbu over the last decade, they are starting to combine into lakes large enough for a small boat to paddle across, Kaplan reports.

"At present, the glacier appears to be disintegrating, and may form a few large and potentially hazardous lakes on the glacier surface," Ann Rowan, who led the field team, tells Navin Singh Khadka for the BBC. Rowan says the Khumbu Glacier is melting at a rate of six feet every year, based on 15 years of satellite images and several field studies.

The problem is that the larger the lakes, the faster the glacier will melt. Water is less reflective than ice, which means that the new lakes trap more heat from the sun, which in turn melts more of the glacial ice, Quincey tells Kaplan. And if the lakes continue to grow, they could pose a risk to Himalayan communities living downstream.

The Khumbu Glacier is far from the only one at risk: According to one recent study, about 5,500 Himalayan glaciers could dramatically retreat or completely melt by 2100, John Vidal reported for The Guardian. And after a 7.8 magnitude earthquake hit the Himalayas on April 25, 2015, the Tsho Rolpa glacial lake just west of Mount Everest was outfitted with a new warning system to alert the 6,000 people living below it in case of a break in the glacier, The Kathmandu Post reported.

It could be decades before the growing glacial lakes pose a risk to people living below the Khumbu Glacier. If the water was to overwhelm the natural dams formed by the glacier, thousands of gallons of water would pour into the villages in the valley below.

But at this point, the scientists just don’t know what will happen—the Khumbu might form a useful reservoir or it could threaten the lives of the people living on Mount Everest’s slopes. “[W]e don’t have really objective methods by which to assess the danger that these lakes pose,” Quincey tells Kaplan.

More research is necessary to understand the fate of these lakes and the Everest communities. Quincy's team will return to the Khumbu Glacier for another survey in May.