The shrinking ice sheet in the Canadian Arctic tells a striking story about how humans could have stopped the planet’s next ice age by burning fossil fuels, according to a new study.
About 20,000 years ago, the once-vast Laurentide Ice Sheet stretched from the Arctic Circle to Illinois and was in places up to three kilometers thick. All that remains is the Delaware-sized Barnes Ice Sheet on Baffin Island in the Canadian territory of Nunavut.
About 2,000 years ago, this ice sheet began to slowly and steadily re-expand. Its growth marked the start of a new period of glaciation, commonly called the Ice Age, according to the new study published in the journal Science.
But around 1960, as human-induced climate change caused summer temperatures to rise, the ice sheet abruptly began to shrink.
“It was just beginning, everything was normal, the next glaciation was about to happen – and yet it stopped,” said Nicolás Young, study author and geochemist at the Lamont-Doherty Earth Observatory, part of the Columbia Climate School. “This is a very powerful example of how we shook up the system.”
For millions of years, the planet has gone in and out of ice ages, due to changes in Earth’s orbit, and the Laurentide Ice Sheet often serves as a starting point.
Young and a group of scientists wanted to understand if the ice sheet had ever been smaller than it is now and then grew back. This is a difficult task because geological evidence is often erased as the ice grows back.
The Barnes Ice Sheet, however, is frozen to its bedrock and does not slide, meaning it has preserved the plants it buried as it grew. Scientists collected long-dead mosses near the edge of the ice sheet and analyzed them to determine when they were last alive. “We can actually track the expansion of the ice margin as it gradually covers the moss and kills it,” Young said.
They also examined nearby rocks to find out how long they have remained ice-free by testing for a rare radioactive isotope that accumulates once a rock is exposed to air.
These techniques helped them piece together a picture of the ice’s past. They found that the ice sheet reached its minimum size about 3,000 years ago, then began to grow back about 2,000 years ago in response to cooler temperatures.
This regrowth should be considered the start of a new ice age, but it never got beyond its infancy before reversing in the 1960s, the study authors say. “We think it’s not a coincidence that this is happening at the same time that we have released an extraordinary amount of greenhouse gases into the atmosphere,” Young said. Climate pollution has “essentially dominated” other mechanisms that “want to cool this region,” he added.
Meredith Kelly, a land science professor at Dartmouth College, who was not involved in the study, said the research applied techniques including “new radiocarbon dating of plants” to give a good idea of the advance and retreat of the ice sheet.
The findings that the Barnes Ice Sheet’s advance suggests the start of an ice age may be accurate, she added, but a comparison with glaciers in other regions that were also advancing at the same time would help to better understand the mechanisms at play.
Andrey Ganopolski, a physicist at the Potsdam Institute for Climate Impact Research, said much research has been done to determine whether carbon pollution could significantly delay the start of the next ice age.
But, he added, other modeling studies, including his own, conclude the next we wouldn’t expect an ice age for about 50,000 years, even without global warming. The growth of the Barnes Ice Sheet “is insufficient to support the conclusion that a new glacial cycle had already begun and was subsequently interrupted,” he said.
Young and his co-authors argue, however, that the first regrowth of the Laurentide Ice Sheet counts as the start of an ice age and that we don’t need to wait for huge ice sheets to form to declare that it has begun.
The findings also shed new light on a controversial period in the 1970s, when some scientists suggested the world could be entering a new ice age, Young said. This idea was picked up by the media, including in a now-infamous Newsweek article titled “The Cooling World,” which warned of a food crisis as the world cooled.
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It’s a time period that skeptics and climate change deniers often cite to discredit scientists as alarmist and incorrect. But Young thinks the new research suggests they were right, that “a new glaciation had in fact begun; it was only just beginning, and now it has stopped.”
Young cautioned that the study should not be interpreted as suggesting that global warming has “saved humanity from an ice age.”
Periods of glaciation occur over very long periods. It would have taken thousands of years before the ice sheet grew to a size where it would have affected people’s daily lives, he said.
Instead, the results reveal the extent to which humans have profoundly disrupted Earth’s systems. Not only did we avoid this ice age, Young said, but “we probably pushed back any possibility of another future glaciation for a very, very long time.”
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