Earth may have quietly begun sliding toward its next ice age about 2,000 years ago, only for human-driven warming to reverse it in the 20th century, according to a new study in the journal Science. The evidence comes from the Barnes Ice Cap on Canada's Baffin Island, the last surviving piece of the vast ice sheet that once buried much of North America.

The researchers found the ice cap shrank to its smallest size sometime after about 3,600 years ago, then began growing again about 2,000 years ago. It reached a maximum around 1960, after which, the authors write, summer warming tipped it into steady ice loss.

The interpretation is contested — and that debate is part of the story. A leading ice age modeler says one regrowing ice cap is not enough to declare that a new glacial cycle had begun, and the study does not change projections that orbital conditions favor a long interglacial. What it adds is unusually direct field evidence of when one ice remnant turned from growth to retreat.

The Ice Sheet That Once Reached Illinois

The Laurentide Ice Sheet covered much of Canada and the northern United States from about 95,000 to 20,000 years ago. At its largest, it stretched from above the Arctic Circle to Illinois and was more than 2 miles thick in places, according to the Columbia Climate School. Its weight and movement helped carve the Great Lakes basins.

What remains is the Barnes Ice Cap, roughly the size of Delaware, on central Baffin Island in Nunavut. Nicolás Young, a geochemist at Columbia's Lamont-Doherty Earth Observatory and the study's first author, led the work with colleague Joerg Schaefer and collaborators including Gifford Miller of the University of Colorado Boulder.

Over the past 2.6 million years, the Laurentide has repeatedly shrunk to this Arctic core during warm periods and regrown during cold ones. That history is why the researchers treat the Barnes Ice Cap as the seed from which a future continental ice sheet would grow.

Reading Time From Rocks and Buried Moss

Most glaciers slide over their beds and grind away evidence. The Barnes Ice Cap is frozen to its bedrock, so as it advanced, it buried plants in place and preserved them. As the ice now retreats, those mosses are reappearing.

The team used two dating clocks. Radiocarbon dating of the uncovered plants shows when they died, which marks when ice overran them. Rocks were tested for beryllium-10, a rare isotope that builds up when cosmic rays strike exposed stone and stops accumulating when ice covers it, ScienceAlert explained. Together, the methods map when ground was exposed and when it was buried.

"It was just getting started, everything was normal, the next glaciation was about to happen, and yet it stopped," Young said. Co-author Schaefer said the site "gave us a rare opportunity to understand how re-glaciation begins and how the Laurentide Ice Sheet re-forms," Smithsonian Magazine reported.

Earth's Orbit Still Sets the Long Clock

Ice ages are paced by slow changes in Earth's orbit and tilt, known as Milankovitch cycles, which shift how much summer sunlight reaches high northern latitudes over tens of thousands of years. Peak warmth after the last ice age came roughly 11,000 to 10,000 years ago in northern regions, driven by those orbital patterns.

That is where the debate lies. Andrey Ganopolski, a physicist at the Potsdam Institute for Climate Impact Research, told CNN that modeling studies, including his own, suggest the next ice age would not be expected for roughly 50,000 years even without global warming. The ice cap's growth, he said, "is insufficient to support the conclusion that a new glacial cycle had already begun and was subsequently aborted."

Young and his colleagues argue that a glacial period should be dated from the first renewed growth of an ice sheet, not from the moment continent-sized ice appears. By their account, it would have taken about 30,000 years for the Laurentide to rebuild its full mass. The disagreement is partly about definitions and partly about how much weight one ice cap's history can carry.

Meredith Kelly, an earth sciences professor at Dartmouth College who was not involved, praised the team's "novel radiocarbon dating of plants" for producing a clear picture of the ice cap's advance and retreat, according to CNN's report. Kelly added that comparing the record with glaciers in other regions would clarify the broader mechanisms.

A Disappearing Archive With Lessons for Today

The more immediate finding is not in dispute. The Barnes Ice Cap has been losing mass since about 1960 because summer melt now exceeds winter snowfall, and the authors link that shift almost entirely to rising summer temperatures. Other ice caps across the Canadian Arctic and North Atlantic are shrinking for similar reasons. Since about 2010, the Barnes Ice Cap has had no accumulation zone at all, meaning no part of its surface now gains more snow in winter than it loses in summer, according to the study's reported findings.

Models project the Barnes Ice Cap could disappear within roughly 300 years. "That will be the true very last remains of the Laurentide, disappearing for good," Young said. Young also cautioned that the study should not be read as global warming having "saved" humanity from an ice age. The same warming is driving rising seas, heat extremes and ecosystem disruption today.

For readers, the takeaway is about timescales — and how quickly one of them changed. Glacial cycles unfold over tens of thousands of years, while the ice cap's reversal happened within a human lifetime. The study is peer-reviewed but rests on one ice cap, and comparisons with other glaciers will test whether its interpretation holds.

What Readers Want to Know

What did the study find? The Barnes Ice Cap, the last remnant of the Laurentide Ice Sheet, reached its smallest size about 3,600 years ago, began regrowing about 2,000 years ago, and started shrinking after reaching a maximum around 1960.

Did humans really cancel an ice age? The authors suggest so, but it is debated. Andrey Ganopolski of the Potsdam Institute says the ice cap's growth is not enough to show a new glacial cycle had begun.

How did scientists date the ice cap's history? They radiocarbon-dated mosses buried and preserved by the advancing ice, and measured beryllium-10 in rocks to see how long they had been exposed or covered.

What drives ice ages? Slow cycles in Earth's orbit and tilt that change summer sunlight at high northern latitudes over tens of thousands of years, along with greenhouse gas levels and ice sheet feedbacks.

Will the Barnes Ice Cap disappear? Models project it could vanish within roughly 300 years at current warming trends.

Does this mean warming is beneficial? No. Lead author Nicolás Young cautioned against reading the study that way, given the present-day impacts of rising temperatures.