Melting glaciers in the Juneau Icefield may be approaching “irreversible tipping point,” new study says

The Mendenhall Glacier is a beautiful sight. To Bethan Davies, a glaciologist at Newcastle University in the United Kingdom, it’s also a reminder.

“It’s the most visible, iconic evidence of climate change,” she said.

It’s no secret that Alaska’s glaciers are shrinking as the burning of fossil fuels warms the planet. But in the Juneau Icefield, home to the Mendenhall and more than a thousand other glaciers, ice has melted especially fast over the last decade — twice as quickly as it did before 2010. 

Davies worries that glaciers in the Juneau Icefield and elsewhere are approaching an irreversible tipping point.

“That means that we would continue to lose ice from Juneau Icefield, even if climate change stops. Even if temperatures stop rising,” she said. “At the moment, we can retain our icefields, but if we cross that tipping point it’s too late.”

The icefield stretches across 1,5000 square miles of mountain terrain between Juneau and British Columbia. It reached its peak volume back in the late 18th century, during a period of cooler temperatures known as the Little Ice Age. 

Since then, almost a quarter of it’s ice volume has melted away. Davies and her colleagues  from universities in the United Kingdom, United State and Europe used satellite imagery, historical photos and decades of glacial measurements to track that decline in a study published in the journal Nature Communications.

They found that glacier volume decreased at a pretty steady pace between 1770 and 1979. Through the tail of the 20th century and the early 2000s, things started to melt a little bit faster. Then, between 2010 and 2020, ice loss accelerated sharply.

And across the icefield, glaciers shrank five times faster from 2015 to 2019 as compared to the mid-20th century.

Every single glacier in the Juneau Icefield is smaller than it was 250 years ago. At least 108 of them have disappeared completely. Those that remain are thinning, receding and breaking into smaller and smaller fragments.

The consequence of all that melting, is more melting. Because the Juneau Icefield is a broad, top-heavy plateau, with ice stretching skyward. When it start to melt, the surface of the icefield slumps down to a lower elevation, where air temperatures are higher.

“And because it’s warmer, it melts more,” Davies said.

The icefield also is at risk of dipping below the snow elevation line. It’s the boundary between seasonal snow and snow that persists year-round, like the white caps on some of Juneau peaks. And it’s moving higher and higher. 

“That means you’re suddenly losing snow, losing nourishment over a really big area of the icefield,” Davies said. “That’s not a healthy thing for a glacier.”

As snowfall decreases and ice breaks apart, the icefield loses some of the reflective, bright white quality that protects it too. 

“You’re left with rock that dark, you’re left with glacier ice that’s maybe a bit gray and a bit dusty,” Davies said. “That absorbs more of the sun’s energy,”

These melt-accelerating processes could be happening to other plateau icefields in Norway, Canada and other parts of the Arctic. The fate of all that ice matters for the whole world.

Glaciers only cover about 1% of the planet.

“But they are currently responsible for about a quarter of sea level rise,” Davies said. “So all the world’s glaciers together are contributing more to sea level rise than the Greenland ice sheet, and more to sea level rise than the Antarctic ice sheet. And the area that’s contributing most from glaciers is Alaska.”

The only way to prevent that sea level rise is to keep water locked in glacial ice. And the only way to do that is to slow the rate of global climate change.

“Every 10th of a degree matters,” Davies said. “If we stick to 1.5 degrees of warming — which is now very close — we’ll retain most of the world’s ice.”