Melt one of them North AmericaThe largest ice fields have accelerated and may become irreversible tipping point. That’s the conclusion of a new research colleague and I have published in Juneau Ice fieldwhich straddles the Alaska-Canada border near the Alaskan capital Juneau.
In the summer of 2022, I ski across a flat, smooth, white ice plain, accompanied by other researchers, sliding in the tracks of the people in front of me under the hot sun. glacier down to the sea, with hundreds of small glaciers on the surrounding mountains.
Our work, now published in Nature Communications, has shown that Juneau is an example of climate “feedback” in action: as temperatures rise, snow falls less and less until summer (technically: “end of summer”. snow line” increases). This causes the ice to be exposed to sunlight and higher temperatures, which means more liquid, less snow, etc.
Like many Alaskan glaciers, the Juneau glacier is the highest, with lots of ice and snow at high altitudes above the late summer snow line. This is before the tongue of the glacier descends. But when the snow line in late summer creeps into the highlands, then suddenly the highest glaciers will melt.
That’s what’s happening now, every summer, and the glaciers are melting faster than ever, causing the ice fields to thin and the highlands to recede. Once the threshold is passed, these feedbacks can accelerate melting and cause ongoing loss of snow and ice, which will continue even if the world stops warming.
The ice is melting faster than ever
Using satellites, photos and old rock piles, we can measure ice loss in the Juneau Icefield from the end of the “Little Ice Age” (about 250 years ago) to the present. We see that the glaciers began to shrink after that cold period ended in about 1770. This ice loss remained constant until about 1979, when it accelerated. It accelerated again in 2010, doubling the previous level. Glaciers there shrank five times faster between 2015 and 2019 than they did from 1979 to 1990.
Our data show that as snowfall decreases and summer melt lengthens, ice fields darken. Fresh white snow is highly reflective, and much of the strong solar energy we experience in the summer of 2022 is reflected back into space. But the summer snow line is finally rising and is now a frequent occurrence on the Juneau Icefield plateau, which means that old glacier snow and ice are exposed to the sun. This slightly darker surface absorbs more energy, increasing snow and ice melting.
As the ice plain thins, the ice and snow reserves at higher elevations are lost, and the surface of the plain descends. This will make it harder for the ice field to stabilize or recover. This is because warmer air at lower elevations causes more melting, leading to an irreversible tipping point.
Long-term data like this is essential for understanding how glaciers behave, and the processes and tipping points that individual glaciers have. This complex process makes it difficult to predict how the glacier will behave in the future.
The hardest jigsaw in the world
We use satellite records to reconstruct how big the glaciers were and how they behaved, but that really limits us to the last 50 years. To come back, we need a different method. To go back 250 years ago, we mapped the moraines, which are large piles of debris deposited at the glacier’s snout, and the places where the glacier has eroded and eroded the bedrock.
To check and build the mapping, we spent two weeks in the ice fields and two weeks in the rainforest below. We camped between moraine ridges, suspending our food high in the air to keep it safe from bears, shouting to warn moose and bears when we bushwhacked through the rainforest, and battling mosquitoes thirsty for our blood.
We used aerial photographs to reconstruct ice fields in the 1940s and 1970s, in the era before satellite imagery was available. This is a high quality photo, but it was taken before the global positioning system made it easy to find exactly where it was taken.
Some also have minor damage over the years – some Sellotape, tears, thumbs. As a result, the individual images must be combined to create a 3D image of the entire ice field. It’s all a bit like doing the world’s hardest jigsaw puzzle.
This kind of work is important because the world’s glaciers are melting so fast – all of them are now losing more mass than Greenland or Antarctica ice sheets, and the rate of glacier thinning worldwide has doubled in the past two decades.
A longer time series shows how this acceleration is occurring. Understanding how and where “feedback” makes glaciers melt faster is important to make better predictions about future changes in this important region.
In the summer of 2022, I ski across a flat, smooth, white ice plain, accompanied by other researchers, sliding in the tracks of the people in front of me under the hot sun. glacier down to the sea, with hundreds of small glaciers on the surrounding mountains.
Our work, now published in Nature Communications, has shown that Juneau is an example of climate “feedback” in action: as temperatures rise, snow falls less and less until summer (technically: “end of summer”. snow line” increases). This causes the ice to be exposed to sunlight and higher temperatures, which means more liquid, less snow, etc.
Like many Alaskan glaciers, the Juneau glacier is the highest, with lots of ice and snow at high altitudes above the late summer snow line. This is before the tongue of the glacier descends. But when the snow line in late summer creeps into the highlands, then suddenly the highest glaciers will melt.
That’s what’s happening now, every summer, and the glaciers are melting faster than ever, causing the ice fields to thin and the highlands to recede. Once the threshold is passed, these feedbacks can accelerate melting and cause ongoing loss of snow and ice, which will continue even if the world stops warming.
The ice is melting faster than ever
Using satellites, photos and old rock piles, we can measure ice loss in the Juneau Icefield from the end of the “Little Ice Age” (about 250 years ago) to the present. We see that the glaciers began to shrink after that cold period ended in about 1770. This ice loss remained constant until about 1979, when it accelerated. It accelerated again in 2010, doubling the previous level. Glaciers there shrank five times faster between 2015 and 2019 than they did from 1979 to 1990.
Our data show that as snowfall decreases and summer melt lengthens, ice fields darken. Fresh white snow is highly reflective, and much of the strong solar energy we experience in the summer of 2022 is reflected back into space. But the summer snow line is finally rising and is now a frequent occurrence on the Juneau Icefield plateau, which means that old glacier snow and ice are exposed to the sun. This slightly darker surface absorbs more energy, increasing snow and ice melting.
As the ice plain thins, the ice and snow reserves at higher elevations are lost, and the surface of the plain descends. This will make it harder for the ice field to stabilize or recover. This is because warmer air at lower elevations causes more melting, leading to an irreversible tipping point.
Long-term data like this is essential for understanding how glaciers behave, and the processes and tipping points that individual glaciers have. This complex process makes it difficult to predict how the glacier will behave in the future.
The hardest jigsaw in the world
We use satellite records to reconstruct how big the glaciers were and how they behaved, but that really limits us to the last 50 years. To come back, we need a different method. To go back 250 years ago, we mapped the moraines, which are large piles of debris deposited at the glacier’s snout, and the places where the glacier has eroded and eroded the bedrock.
To check and build the mapping, we spent two weeks in the ice fields and two weeks in the rainforest below. We camped between moraine ridges, suspending our food high in the air to keep it safe from bears, shouting to warn moose and bears when we bushwhacked through the rainforest, and battling mosquitoes thirsty for our blood.
We used aerial photographs to reconstruct ice fields in the 1940s and 1970s, in the era before satellite imagery was available. This is a high quality photo, but it was taken before the global positioning system made it easy to find exactly where it was taken.
Some also have minor damage over the years – some Sellotape, tears, thumbs. As a result, the individual images must be combined to create a 3D image of the entire ice field. It’s all a bit like doing the world’s hardest jigsaw puzzle.
This kind of work is important because the world’s glaciers are melting so fast – all of them are now losing more mass than Greenland or Antarctica ice sheets, and the rate of glacier thinning worldwide has doubled in the past two decades.
A longer time series shows how this acceleration is occurring. Understanding how and where “feedback” makes glaciers melt faster is important to make better predictions about future changes in this important region.
