The next ice age began 2,000 years ago, then global warming stopped it

Earth had already started sliding into its next ice age, and the proof was frozen under a single Arctic glacier. Dead moss and dwarf shrubs melting out of the Barnes Ice Cap on Canada’s Baffin Island show that the last surviving piece of North America’s great ice sheet stopped shrinking long ago and began to grow again, the first step of a new glacial period.

Then the growth stopped. Within a single human lifetime, summer warming driven by greenhouse gases flipped the ice cap from advance to retreat, and it has been losing ground ever since. That is the conclusion of a new study in the journal Science led by geochemist Nicolás Young of Columbia University’s Lamont-Doherty Earth Observatory, with glacial geologist Gifford Miller of the University of Colorado Boulder and nine other colleagues.

The finding turns a long-running thought experiment into field evidence. Paleoclimate researchers have talked for years about a “failed ice age”, the idea that the slow orbital rhythm that paces glaciations was already pushing the planet toward cold when industrial emissions overrode it. The plants under the Barnes Ice Cap put a date on when that cold phase began and when it ended.

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“It’s a very powerful example of how we have jolted the system,” Young said in a statement from Columbia. Miller put it more bluntly: “It’s an illustration of the real power of greenhouse gases.”

How dead moss dates a growing glacier

The method depends on an unusual property of the Barnes Ice Cap. It is frozen solid to the bedrock beneath it, so it does not slide and scour the ground the way most glaciers do. When its edge creeps forward, it simply buries the tundra in place, entombing mosses and small shrubs that can survive intact for thousands of years.

Since the ice margin started retreating, those plants have been reappearing at the melting edge. The team collected them, starting with fieldwork in 2022, and radiocarbon dated each sample. Carbon-14, a weakly radioactive form of carbon that living plants absorb from the air, decays at a known rate after death, so the age of a plant gives what Young calls a kill date. “These mosses were growing on the landscape and then all of the sudden the ice cap expands and covers them,” he said. “That radiocarbon age tells you the timing of when ice killed the plant.”

The researchers set themselves two tests. If a new glaciation had really begun, the buried plants should all have died within the last few thousand years. And the sequence should run in order, with the plants entombed first sitting nearest the ice and progressively younger kill dates farther out, tracing an advancing front. Both predictions held. The team added samples from smaller ice caps in the region that have recently melted away entirely.

The resulting timeline, as summarised in the paper’s abstract, is clean. The Barnes Ice Cap reached its smallest size sometime after about 3,600 years ago. It began expanding again about 2,000 years ago, kept growing for roughly two millennia and reached its maximum around 1960. A sharp trimline, a boundary between dark, lichen-covered rock and bare pale rock, still marks that high point on the landscape around the ice.

The ice sheet that once reached the American Midwest

The Barnes Ice Cap is the last remnant of the Laurentide Ice Sheet, the largest of the great ice sheets of the last glacial period. Between roughly 95,000 and 20,000 years ago the Laurentide covered most of Canada and the northern United States, reaching as far south as Illinois and Indiana, and in places it was more than three kilometres thick. Today what is left is an ice cap roughly the size of the US state of Delaware in central Baffin Island, in the territory of Nunavut.

“People always say that it disappeared, but that’s not true,” Young said. Because the Laurentide has repeatedly shrunk back to this Arctic core and then regrown over the past 2.6 million years, the Barnes Ice Cap is the natural seed from which the next continental ice sheet would grow.

Strictly speaking, Earth is still in an ice age, the Late Cenozoic Ice Age that began about 34 million years ago, and within it cold glacial periods alternate with warm interglacials like the one we live in now. What most people call “the next ice age” is the next glacial period. The last one ended about 11,700 years ago.

The cold phase the plants record would not have been dramatic on a human timescale. According to Young, the cooling would have taken thousands of years to become noticeable, and the Laurentide about 30,000 years to regain its continental size. The study captures only the first step, the moment the ice stopped retreating and began to accumulate.

The stable glacier that fooled the first surveys

The timeline also explains an old puzzle. The first scientific studies of the Barnes Ice Cap, in the 1950s and 1960s, described a glacier in near-perfect balance, neither growing nor shrinking. That observation entered the literature as evidence that the ice cap was stable.

According to the new reconstruction, those surveys caught a rare standoff: falling summer sunlight from Earth’s orbit was pushing the ice to grow, while rising greenhouse gases were pushing it to melt. “It turns out this was the only time in history it was ever in equilibrium,” Miller said. “It made it into the literature that the ice cap was stable, it never changed,” he added, calling it “a false conclusion built on good data.”

The same cooling, which lasted from the 1950s to the mid-1970s, fed the famous warnings of an imminent ice age. Miller remembers a field season in 1972 off Baffin Island when the sea ice never broke up and his team had to hike out to a military airstrip. By the end of that decade, the evidence for greenhouse warming had won out. “It actually was happening,” Young said of the predicted glaciation. “They couldn’t quite prove it, but now we sort of have the evidence.”

What the study doesn’t settle

The boldest claim in the paper is a matter of definition as much as data. Young and his colleagues argue that the first renewed growth of the Laurentide’s last remnant should count as the onset of a glacial period, even though no continental ice sheet ever formed. Previous model-based studies placed the next glaciation thousands or even tens of thousands of years in the future, because they defined its start by large-scale ice growth rather than by one ice cap turning around.

Many Arctic glaciers advanced during the last few thousand years, a cooling phase glaciologists call the Neoglacial, and some of that advance was regional. Whether the expansion of one ice cap on Baffin Island was the opening of a planet-wide glaciation or a long cold spell within the current interglacial is something the plant dates alone cannot decide. A Perspective article by Shaun Marcott of the University of Wisconsin-Madison, published in the same issue of Science, frames the result more cautiously: its summary says global warming “may have forestalled” the next glaciation.

There are also limits to what kill dates can show. They record when the ice edge reached a given spot, not how much ice the cap gained overall, and the attribution of the post-1960 retreat to human-caused warming rests on its timing and on the ice cap’s shift to losing more mass each summer than it gains each winter, as the abstract describes, while the decline in orbital summer sunlight continued.

Common questions about the next ice age

Are we living in an ice age right now?

Technically yes. Earth has been in the Late Cenozoic Ice Age for about 34 million years, with permanent ice at the poles. Within it, cold glacial periods alternate with warmer interglacials, and we are in an interglacial that began about 11,700 years ago.

When was the next ice age supposed to start?

It depends on the definition. This study argues that the next glacial period began about 2,000 years ago, when the Barnes Ice Cap started to regrow. Climate models that define a glaciation by large-scale ice growth had put it thousands to tens of thousands of years in the future.

What is the Barnes Ice Cap?

It is an ice cap roughly the size of Delaware on central Baffin Island in Nunavut, Canada, and the last surviving remnant of the Laurentide Ice Sheet that covered much of North America during the last glacial period.

Will the next ice age come back if warming stops?

Not on any human timescale. Scientists cannot say when the next glaciation might begin in a world with elevated greenhouse gas concentrations, and models suggest the Barnes Ice Cap itself will be gone within a few centuries.

What comes next

The study was published in Science on 22 October 2026. Models of the glacier’s future project that the Barnes Ice Cap will melt away completely within the next few centuries, removing the seed from which the Laurentide has regrown at the start of past glaciations. If continental ice sheets ever begin to grow again, they may have to start without it. “That will be the true very last remains of the Laurentide, disappearing for good,” Young said.

Reference: Young et al., “Late Holocene reexpansion of the Laurentide Ice Sheet,” Science, 2026. DOI: 10.1126/science.aed3379

Tags: climate, Ice Age, glaciers, Baffin Island, Barnes Ice Cap, global warming

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