One of the largest areas of connected glaciers in North America is melting twice as fast as before 2010, a team of scientists said Tuesday, an “incredibly worrying” sign that land ice in many places may be disappearing even sooner than previously thought. .
The Juneau Ice Field, which stretches across the Coast Mountains of Alaska and British Columbia, lost 1.4 cubic miles of ice annually between 2010 and 2020, researchers estimated. That’s a sharp acceleration from previous decades and even sharper compared to the middle of the 20th century or earlier, the researchers said. Overall, the ice field has shed a quarter of its volume since the late 18th century, part of a period of glacial expansion known as the Little Ice Age.
As societies add more and more planet-warming carbon dioxide to the atmosphere, glaciers in many regions could exceed tipping points beyond which their melting accelerates, said Bethan Davies, a glaciologist at Newcastle University in England who led the new research.
“If we reduce the carbon, then we have a better chance of maintaining these beautiful ice masses,” said Dr. Davies. “The more carbon we put in, the more we risk their irreversible and complete removal.”
The fate of the Alaskan ice is extremely important to the world. No other region of the planet is predicted to contribute more to global sea-level rise this century than melting glaciers.
The Juneau Ice Field covers 1,500 square miles of rugged terrain north of Juneau, the state capital. The region has warmed and rained over the past half-century, meaning a longer melting period for glaciers and less snow to replenish them.
The ice field includes 1050 glaciers. Or at least in 2019 it was.
Dr. Davies and her colleagues combined decades of glacier measurements with information from satellite images, aerial photographs, maps and surveys to reconstruct how the ice evolved over the previous two and a half centuries. They looked at tree-ring studies and peat to understand past environments. They also went out on the ice themselves to double-check what they had seen from the satellites.
The changes they revealed are extensive.
The researchers found that every one of the ice field’s glaciers retreated between 1770 and 2019. More than 100 glaciers have completely disappeared. Nearly 50 new lakes have formed as glaciers melt and collect water.
The researchers also found that the rate at which the ice field was losing volume slowed somewhat in the mid-20th century. It picked up after 1979 and accelerated further after 2005.
The acceleration could be related to how the ice’s whiteness — its albedo, as glaciologists call it — affects melting and vice versa, the researchers say. As the snow recedes, more rocks and boulders are exposed in the ice. These dark colored surfaces absorb more sunlight, causing the ice around them to thin even faster. Tourism and wildfires also deposit soot and dust on the surface of the glacier, further accelerating melting.
Another factor, said Dr. Davies and her colleagues, is that as the ice field thins, more of its area lies at a lower altitude. This exposes more of its wide, flat surface to warmer air, making it thinner even faster.
Scientists have been aware that glacier melt is affected by these kinds of self-enforcing feedbacks, said Martin Truffer, a physicist at the University of Alaska Fairbanks who was not involved in the new research. But overall, models of glacier change still don’t include enough of these physical complexities, said Dr. Davies. “If you want to know how this ice field is going to behave, you want to know that the physics is realistic,” she said.
Still, she added, science is moving forward quickly. Last year, researchers released projections of how every glacier on Earth will evolve depending on what humanity does or doesn’t do about global warming.
The scientific achievement was significant, even if the conclusion was not encouraging. According to projections, even if nations meet the Paris Agreement’s goal of limiting warming to 1.5 degrees Celsius above pre-industrial conditions, roughly half of the world’s glaciers, about 104,000 of them, could be gone by 2100.