Humans halted the next ice age in the 1960s, study of Canada's last Ice Age remnant finds

About 2,000 years ago, Earth quietly began slipping into its next ice age. The evidence was there in a patch of ice on a Canadian island — slowly thickening, spreading across the tundra, burying the mosses beneath it. Then, in the 1960s, it stopped. A new study published in the journal Science argues that what stopped it was us.

It was just getting started, everything was normal, the next glaciation was about to happen — and yet it stopped. It's a very powerful example of how we have jolted the system.— Nicolás Young, geochemist and lead author, Columbia University

The study centers on the Barnes Ice Cap (BIC), a glacier on Baffin Island in Nunavut, Canada, roughly the size of Delaware. It is the last surviving remnant of the Laurentide Ice Sheet — the vast continental glacier that, at its peak, buried all of Canada and reached as far south as New York and the American Midwest under up to three kilometers of ice. That sheet began retreating around 12,000 years ago, eventually dwindling to the Barnes Ice Cap. For scientists, the BIC is not just a curiosity; it is a living archive of glacial history.

To read that archive, Young and his colleagues used two atomic dating methods. First, they measured concentrations of beryllium-10 — an isotope produced when cosmic radiation strikes exposed rock — in stones near the glacier's edge. When ice advances and covers rock, beryllium-10 stops accumulating; when ice retreats and rock is re-exposed, accumulation resumes. This allowed the team to calculate that the ice cap first shrank to roughly its modern size around 3,600 years ago. Second, they analyzed ancient vegetation — mosses and lichens — that the retreating ice had preserved and then uncovered. Because dead plants no longer absorb carbon, their carbon-14 ratios act as a stopwatch, marking the moment the ice entombed them.

Together, the two methods produced a timeline. The Barnes Ice Cap reached its minimum extent around 3,000 years ago, then held that size before beginning to expand again around 2,000 years ago. The researchers interpret that expansion as the natural onset of the next glacial period — driven by Milankovitch cycles, the periodic shifts in Earth's orbital shape, axial tilt, and rotational direction that govern how much sunlight reaches different parts of the planet.

After the ice cap retreated, mosses eventually colonized this newly exposed land. These mosses are living there, and things are normal — then, eventually, the ice cap starts to re-expand. The ice covers the moss, and kills it.— Nicolás Young, paleoclimatologist, Lamont-Doherty Earth Observatory, Columbia University

The ice cap grew for roughly 2,000 years. Then, according to the study, it reached its historical maximum around 1960 — and reversed. Historic aerial photographs confirm the retreat. Since the 1980s, the Barnes Ice Cap's edges have pulled back an average of four meters per year. The researchers attribute the reversal to rising summer temperatures driven by anthropogenic greenhouse gas emissions, which they trace back to around 1750 and the start of the Industrial Revolution. By the 1960s, the ice was losing more mass each summer than it could regain each winter.

Modern retreat of this glacier has reversed 2,000 years of net expansion — that's a pretty decent chunk of time.— Nicolás Young, paleoclimatologist, Lamont-Doherty Earth Observatory, Columbia University

The implications extend well beyond one ice cap. The Laurentide Ice Sheet was the largest glacial structure of the Pleistocene epoch, and researchers suggest the Barnes Ice Cap functioned as its seed — the nucleus from which a new continent-spanning sheet could have grown. If the BIC disappears, that seed is gone. Climate models cited in the study suggest the ice cap will vanish entirely within the next 300 years.

That will be the true very last remains of the Laurentide, disappearing for good. What has been an extremely natural and predictable phenomenon is now gone.— Nicolás Young, geochemist, Columbia University

An outside researcher called the findings significant. Andrew Wickert, an associate professor of environmental science at the University of Minnesota Twin Cities who was not involved in the study, told Wired: "Even as we were just starting to ramp up emissions, we've already done enough damage to cause the major North American ice sheet to already start retreating. That's significant." Meredith Kelly, a professor of earth sciences at Dartmouth, described the data as "awesome" and the pattern as clear, but told Wired she would like to see comparisons with other sites around the world to more fully understand the mechanisms of glacial inception.

The study also revisits a decades-old episode in climate science history. In the early 1970s, scientists met at Brown University to discuss when the next ice age might begin and concluded a glaciation was imminent enough to send a warning letter to President Richard Nixon. Media coverage of that meeting, combined with a cooler stretch of weather in the 1970s, has since been used by climate change deniers as supposed evidence that global warming is not real. Young notes that two of his co-authors were at that original meeting, and argues the new research vindicates rather than contradicts what those scientists concluded: a glaciation was indeed beginning — it was human emissions that ended it.

A perspective piece accompanying the study in Science, written by glaciologist and University of Wisconsin-Madison professor Shaun Marcott, states that continued greenhouse gas emissions could forestall the next ice age for hundreds of thousands of years — a timescale that would represent a fundamental alteration of one of Earth's longest-running natural cycles.

Why it matters — The study provides the most concrete physical evidence yet that human greenhouse gas emissions have overridden one of Earth's fundamental orbital cycles, with a perspective piece warning that continued emissions could delay the next ice age by hundreds of thousands of years — permanently altering the planet's long-term climate rhythm.

Reported by science.org, sciencealert.com, wired.com, gizmodo.com