Greenhouse Gases Derailed an Ice Age That Had Already Begun 2,000 Years Ago

An Ice Age Quietly Started — Then Humans Stopped It

About 2,000 years ago, Earth began slipping into a new ice age. Slowly but surely, ice was advancing across the Arctic, following a rhythm that had governed the planet for millions of years. Then something unprecedented happened: humans burned enough fossil fuels to reverse it entirely. A new study published in the journal Science suggests that a new glacial period was beginning some 2,000 years ago, but by the 1960s, greenhouse gas emissions had raised global temperatures enough to reverse it.

Lead author and Columbia University geochemist Nicolás Young put it plainly: "It was just beginning, everything was normal, the next ice age was about to start, but it stopped. This is a very powerful example of how we have shaken the entire natural system." It's a statement that reframes the entire climate conversation — not just as a warning about the future, but as a revelation about what has already happened.

The Clue Frozen in Canada's Arctic

Researchers reconstructed the growth and retreat of Canada's Barnes Ice Cap, which was once part of a massive stretch of ice called the Laurentide Ice Sheet. The last vestige of the Laurentide still survives as the Barnes Ice Cap, a Delaware-sized ice cap located on central Baffin Island in the Canadian territory of Nunavut. What makes this site so scientifically valuable is what's frozen inside it.

The Barnes Ice Cap is frozen directly to its underlying bedrock. Unlike most glaciers, it does not slide, and thus preserves the vegetation that grew at earlier times when the glacier was small and was subsequently entombed by its expansion. The team obtained 88 new radiocarbon ages from previously buried vegetation near the Barnes margin, essentially reading the ice cap's diary entry by entry. The combined evidence suggests the ice reached its smallest configuration between about 3,000 and 2,000 years ago, and its minimum extent was smaller than the ice cap's present dimensions — showing that today's retreat is uncovering ground exposed during an earlier warm interval.

The Moment Industrialization Changed Everything

The timeline researchers put together suggests that the ice cap started to expand around 2,000 years ago — a sign a new ice age was beginning — but it was cut short by planet-warming industrialization in the 1960s. The study reported that the ice cap margin retreated by about 200 to 800 meters between approximately 1960 and 2022, depending on the location. That's not a slow, geological drift — that's a sharp reversal tied directly to human activity.

The findings also offer a surprising vindication to scientists from a previous era. The findings are described as a coda for climate scientists who in the 1970s made the controversial claim that a new ice age was imminent. "It actually was happening," Young says. "They couldn't quite prove it, but now we sort of have the evidence." Those researchers were mocked for decades. It turns out they were right — they just couldn't see the proof that was locked under the ice.

What This Means for Earth's Future

Future emissions could forestall the next ice age for hundreds of thousands of years, altering one of Earth's most fundamental natural cycles. The Barnes Ice Cap itself is now projected to disappear within the next few centuries. The very geological archive that helped scientists make this discovery is melting away.

While the study shows that greenhouse gases have forestalled the cycle, it does not definitively say it is impossible to restart. However, given the scale of the warming and the potential for hundreds of thousands of years of delay, it would require a massive and sustained reduction in global temperatures to allow natural orbital cycles to regain dominance. In other words, humanity has become a force of nature in the most literal sense — capable of overriding the gravitational choreography of Earth's own orbit around the Sun. Whether that power is cause for alarm, or for awe, is a question worth sitting with.