An icefield is a collection of glaciers, while an ice sheet is something continent-wide and only two of those remain, in Greenland and Antarctica. The most famous glacier in the Juneau icefield is the Mendenhall Glacier, a tourist hotspot. The Arctic is warming about four times faster than the rest of the globe with Alaska warming 2.6 degrees since 1980, according to federal weather data.

“When you go there the changes from year-to-year are so dramatic that it just hits you over the head,” Pelto said.

Pelto first went to the Juneau icefield in 1981 to try to make the U.S. ski team and has continued to study it since, giving up competitive skiing for research.

“In 1981, it wasn’t too hard to get on and off the glaciers. You just hike up and you could you could ski to the bottom or hike right off the end of these glaciers,” Pelto said. But now they’ve got lakes on the edges from melted snow and crevasses opening up that makes it difficult to ski, he said.

It’s also now like a staircase of bare rocks there, Pelto said. White snow and ice reflect the sun’s heat, the dark rocks absorb it, making the ground warmer, melting more snow in a feedback effect that amplifies and accelerates the warming-triggered melt, the study said.

Key is the snow elevation line. Below the snow line, snow can disappear in the summer, but there’s snow cover year-round above. That snow line keeps moving upward, Pelto said.

The shape of Juneau’s icefield, which is rather flat, “makes it vulnerable to particular tipping points” because once the snow line moves up, large areas are suddenly more prone to melt, Davies said.

“The tipping point is when that snow line goes above your entire icefield, ice sheet, ice glacier, whichever one,” Pelto said. “And so for the Juneau icefield, 2019, 2018, showed that you are not that far away from that tipping point.”

Even if all the snow in the Juneau icefield would melt, and that’s a long way away, it would not add much to global sea levels, Pelto said. But it is a big tourist destination and cultural hot spot, Davies said.

“It is worrisome because in the future the Arctic is going to be transformed beyond contemporary recognition,” said Julienne Stroeve, a University of Manitoba ice scientist who wasn’t part of the study. “It’s just another sign of a large transformation in all the ice components (permafrost, sea ice, land ice) that communities depend on.”

Davies said the team was able to get such a long-term picture of the icefield’s melting from satellite images, airplane overflights, pictures stored away in drums in a warehouse and historical local measurements, stitching them all together like a giant jigsaw puzzle with most of the pieces being nearly all white.

Five different outside experts said the research made sense and fits with other observations. Michael Zemp, head of the World Glacier Monitoring Service, said it shows “that we need urgent and tangible actions to save at least some of the remaining ice.”

“We’re 40 years from when I first saw the glacier. And so, 40 years from now, what is it going to look like?” Pelto said. “I do think by then the Juneau icefield will be past the tipping point.”

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