The melting of one of North America’s largest ice sheets is accelerating and may soon reach an irreversible tipping point. New Research My colleagues and I published a paper on the Juneau Icefield, which straddles the Alaska-Canada border near the Alaska capital of Juneau.
In the summer of 2022, I skied across the flat, smooth, white plateau of the ice fields. Other ResearchersUnder the hot sun, I ski in the footsteps of those ahead of me. From the plateau, some 40 huge, interconnected glaciers flow down to the sea, with hundreds of smaller ones on the surrounding mountain peaks.
Our research is currently Nature Communicationsshows that Juneau is an example of a climate “feedback” at work: As temperatures rise, less and less snow remains during the summer (technically, the “late-summer snow line” is rising). This exposes the ice to more sunlight and warmer temperatures, making it more susceptible to melting, resulting in less snow, and so on.
Like many glaciers in Alaska, Juneau’s glacier is top-heavy, with a large amount of ice and snow high above the late-summer snowline that previously supported the lower glacial tongue, but as the late-summer snowline rises above the upper plateau, suddenly a large amount of the top-heavy glacier becomes exposed to new melting.
That’s what’s happening right now: each summer glaciers melt much faster than before, the ice fields get thinner and thinner, and the plateau gets lower and lower. Once a threshold is crossed, these feedbacks accelerate glacier melting, leading to a permanent loss of snow and ice that would continue even if global warming were to stop.
The ice is melting faster than ever before
Using satellites, photography, and old rock piles, we were able to measure ice loss across the Juneau Ice Field from the end of the last “Little Ice Age” (about 250 years ago) to the present. We found that the glaciers began to shrink after that cold period ended around 1770. This ice loss remained constant until about 1979, then accelerated. In 2010 it accelerated again, twice as fast as before. Between 2015 and 2019, the glaciers there shrunk five times faster than they did from 1979 to 1990.
Our data shows that as snow falls and the summer melt season lengthens, the ice field is getting darker. New, white snow is highly reflective, so much of the intense solar energy experienced in the summer of 2022 is reflected back into space. However, the late summer snow line is rising and is now more frequent on the Juneau Ice Field plateau. This means that older snow and glacial ice are more exposed to the sun. These slightly darker surfaces absorb more energy, resulting in increased snow and ice melt.
As the ice plateau thins, higher ground ice and snow reserves are lost and the plateau surface lowers, making it increasingly difficult for the ice plateau to stabilize or even recover, as warmer air at low altitudes encourages further ice melt, leading to an irreversible tipping point.
Such long-term data is essential to understand glacier behavior and the processes and tipping points that exist within individual glaciers. These complex processes make it difficult to predict how glaciers will behave in the future.
The most difficult jigsaw puzzle in the world
We’ve used satellite records to reconstruct the size and movement of glaciers, but this only covers the last 50 years. To go back further, we need a different method. To go back 250 years, We mapped the moraine ridge.These include large piles of debris that have accumulated at the head of a glacier, or places where a glacier has scraped and worn the bedrock.
Checking our maps and exploring further, we spent two weeks on the ice field and two weeks in the rainforest below. We camped between moraine ridges, hung high in the air to protect our food from bears, and bushwhacked through the rainforest, yelling warnings to moose and bears to stay away, battling mosquitoes that were thirsty for our blood.
We used aerial photographs to reconstruct what the ice fields looked like in the 1940s and 1970s, in an era before satellite imagery was readily available. These are high-quality photographs, but they were taken before GPS made it easy to pinpoint locations.
Some of the photos also had some damage in the process – tape, rips, fingerprints – so the individual photos had to be pieced together to create a 3D image of the entire ice field – a task that was like solving the world’s most difficult jigsaw puzzle.
Such efforts are crucial because the world’s glaciers are melting rapidly. They are currently losing more mass than the Greenland and Antarctic ice sheets, and the rate of glacial thinning worldwide is It has doubled in the past 20 years.
Longer time series data show how significant this acceleration is. Understanding how and where “feedbacks” are causing glacier melt to accelerate further is essential to more accurately predict future changes in this important region.
Bethan DavisSenior Lecturer in Physical Geography, Newcastle UniversityThis article conversation Published under a Creative Commons license. Original Article.
