A shrinking ice cap in Arctic Canada tells a striking story of how humans may have halted the planet’s next ice age by burning fossil fuels, according to new research.

Around 20,000 years ago, the once vast Laurentide Ice Sheet sprawled from the Arctic Circle as far south as Illinois and was up to two miles thick in parts. All that remains of it now is the Delaware-sized Barnes Ice Cap on Baffin Island in Canada’s Nunavut territory.

Roughly 2,000 years ago, this ice cap started to slowly and steadily re-expand. Its growth marked the start of a new period of glaciation, commonly called an ice age, according to the new study published in the journal Science.

But around 1960, as human-driven climate change pushed up summer temperatures, the ice cap abruptly began to shrink.

“It was just getting started, everything was normal, the next glaciation was about to happen — and yet it stopped,” said Nicolás Young, a study author and a geochemist at the Lamont-Doherty Earth Observatory, part of the Columbia Climate School. “It’s a very powerful example of how we have jolted the system.”For millions of years the planet has moved in and out of ice ages, driven by shifts in Earth’s orbit, and the Laurentide Ice Sheet often serves as a starting point.

Young and a group of scientists wanted to understand whether the ice sheet had ever been smaller than it currently is and then regrown. It’s a tough task as geological clues are often erased as ice regrows.

The Barnes Ice Cap, however, is frozen to its bedrock and doesn’t slide, meaning it has preserved the plants it entombed as it grew. The scientists gathered long-dead mosses near the ice cap’s edge and analyzed them to figure out when they were last alive. “We can actually track the expansion of the ice margin as it’s progressively covering mosses and killing (them),” Young said.

They also examined nearby rocks to find out how long they had been ice-free by testing for a rare, radioactive isotope that accumulates once a rock is exposed to air.

The techniques helped them reconstruct a picture of the ice’s past. They found the ice sheet reached its minimum size about 3,000 years ago, then started to regrow roughly 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 past its infancy before it reversed course in the 1960s, the study authors argue. “We think that it’s no coincidence that that’s at the same time as we’ve pumped an extraordinary amount of greenhouse gases into the atmosphere,” Young said. Climate pollution has “essentially overpowered” the other mechanisms that “want to make that region cool,” he added.

Meredith Kelly, an earth sciences professor at Dartmouth College, who was not involved with the study, said the research applies techniques including “novel radiocarbon dating of plants” to set out a good picture of the ice cap’s advance and retreat.

The conclusions that the advance of the Barnes Ice Cap suggests the start of an ice age could be right, she added, but a comparison with glaciers in other regions that were also advancing at a similar time would help to understand more about the mechanisms at play.

Andrey Ganopolski, a physicist at the Potsdam Institute for Climate Impact Research, said there has been plenty of research into whether carbon pollution may significantly delay the onset of the next ice age.

But, he added, other modeling studies, including his own, conclude the next ice age wouldn’t be expected for another 50,000 years or so — even without global warming. The growth of the Barnes Ice Cap “is insufficient to support the conclusion that a new glacial cycle had already begun and was subsequently aborted,” he said.

Young and co-authors, however, argue the first regrowth of the Laurentide Ice Sheet counts as the start of an ice age and we don’t need to wait for the formation of enormous ice sheets to declare one has begun.

The findings also throw new light on a controversial period in the 1970s, when some scientists suggested the world might be entering a new ice age, Young said. This idea was picked up by the media, including a now infamous article in Newsweek with the headline “The Cooling World,” which warned of a food crisis as the world chilled.

It’s a period climate change skeptics and deniers often reference to discredit scientists as alarmist and incorrect. But Young believes the new research suggests they were right, that “a new glaciation actually had started; it was just getting going, and now it’s stopped.”

Young cautioned that the study should not be interpreted as suggesting global warming has “saved humanity from an ice age.”Periods of glaciation happen over very long time frames. It would have taken thousands of years before the ice cap would have approached a size where it would have affected people’s everyday lives, he said.

Instead, the findings reveal just how profoundly humans have pushed Earth’s systems out of whack. Not only have we avoided this ice age, Young said, but “we’ve probably put off any chance of any other future glaciation for a very, very long time.”