One of North America’s largest areas of interconnected glaciers is melting twice as fast as before 2010, a team of scientists said Tuesday, in what they called an “extremely worrying” sign that the land’s ice in many countries may disappear even faster than previously thought. .
The Juneau Ice Field, which stretches across the coastal mountains of Alaska and British Columbia, lost 1.4 cubic miles of ice per year between 2010 and 2020, the researchers estimated. That’s a sharp acceleration from previous decades, and even sharper when compared to the mid-20th century or earlier, the scientists said. However, the ice field has shed a quarter of its volume since the late 18th century, which was 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 areas may pass tipping points beyond which their melting accelerates rapidly, said Bethan Davies, a glaciologist at the University of Newcastle in England, who led the new research.
“If we reduce the carbon, then we have more hope of maintaining these amazing ice masses,” said Dr. Davies. “The more carbon we put in, the more we risk their irreversible and complete removal.”
The fate of Alaska’s ice is of tremendous importance to the world. In no other region of the planet is melting glaciers projected to contribute more to global sea-level rise this century.
The Juneau Icefield covers 1,500 square miles of rugged landscape north of Juneau, the state capital. The region has become warmer and rainier over the past half-century, meaning a longer melting season for glaciers and less snow to replenish them.
The ice field includes 1050 glaciers. Or at least it did in 2019.
To reconstruct how the ice evolved over the previous two and a half centuries, Dr. Davies and her colleagues combined decades of glacier measurements with information from satellite images, aerial photographs, maps and surveys. They looked at tree-ring studies and peat to understand the past environment. They also went out on the ice themselves to double-check what they saw from the satellites.
The changes they have discovered are sweeping.
Every single one of the ice field’s glaciers retreated between 1770 and 2019, the scientists found. More than 100 glaciers disappeared completely. Nearly 50 new lakes were formed when the glaciers melted and the water accumulated.
The scientists also found that the rate at which the ice field lost volume slowed somewhat in the mid-20th century. It increased after 1979, then accelerated further after 2005.
This acceleration, the scientists said, may have to do with how the ice’s whiteness — its albedo, as glaciologists call it — affects melting and vice versa. As snowfall decreases, more rocks and boulders in the ice are exposed. These dark colored surfaces absorb more solar radiation, causing the ice around them to melt even faster. Tourism and wildfires are also depositing soot and dust on the surface of the glaciers, further accelerating the 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 the warmer air, making it thin 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. In general, however, models of glacial change still do not 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.
However, she added, science is advancing rapidly. Last year, researchers released projections of how each glacier on Earth will evolve depending on what humanity does or fails to 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, some 104,000 of them, could disappear by 2100.