Climate change has erased two millennia of progress toward another global ice age glaciation, potentially lending new context to controversial predictions of global cooling from the 1970s.
In a recent paper published in Science, researchers show that approximately 2,000 years ago, a remnant of the vast ice sheet that covered much of North America during the last glacial period began expanding again, until rising temperatures reversed that growth in the 1960s.
Technically, Earth remains in an ice age, characterized by alternating periods of extensive glaciation and warmer interglacial conditions. Over the last two billion years, our planet has experienced at least five major ice ages that reshaped landscapes, lowered sea levels, and transformed life on Earth.
Ice Age Extremes
“It was just getting started, everything was normal, the next glaciation was about to happen—and yet it stopped,” said Nicolás Young, 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.”
The researchers investigated the Laurentide Ice Sheet, which once extended from the Arctic Circle to present-day Illinois and reached a thickness of two miles in some areas. The ice sheet underwent major expansion during the last glacial period, which spanned approximately 95,000 to 20,000 years ago. Today, one of its last remnants is the Barnes Ice Cap, situated on Baffin Island in Canada and roughly the size of Delaware, the second-smallest U.S. state.
Their primary question was whether the ice sheet had ever recovered and begun expanding again after shrinking to an extent smaller than its present size. Although the ice sheet has advanced and retreated throughout the glacial cycles of the last 2.6 million years, it remained unclear just how unusual its current reduction might be.
Uncovering The Glacial Past
The impermanence of ice makes reconstructing glacial history challenging. Melting and movement can obscure evidence of previous ice margins, making it difficult to identify periods of maximum retreat and subsequent expansion.
Fortunately, the Barnes Ice Cap is largely frozen to its underlying bedrock, limiting the movement that can erase clues about its history. This means vegetation preserved beneath the ice can remain in the same location where it originally grew before being covered by an advancing ice margin.
Using radiocarbon dating, the researchers analyzed preserved vegetation exposed by the ice cap’s retreat, including material that began emerging during the 1960s.
“If you do this enough times, you can actually develop a timeline of that ice margin systematically advancing over plants,” Young explained. “You’re actually tracking the expansion of that ice margin.”
The researchers then compared the Barnes Ice Cap findings with vegetation dating from other ice caps, arriving at a surprising conclusion: the ice reached its last minimum extent approximately 3,000 years ago before beginning to expand again around 2,000 years ago.
A Last Ice Age
The team argues that the renewed expansion of existing ice masses, rather than the eventual formation of large continental ice sheets, could be considered an early stage in the onset of glaciation. This interpretation challenges conventional expectations about the timing of Earth’s next glacial period.
While other researchers have modeled the next major glaciation as beginning thousands of years in the future, the new study suggests that an initial phase of ice expansion may already have begun two millennia ago, before being interrupted by modern warming.
The findings also offer an intriguing perspective on controversial predictions of global cooling made by some scientists during the 1970s. At the time, researchers debated the relative influences of natural climate variability, atmospheric aerosols, and increasing greenhouse gas concentrations, although scientific evidence increasingly favored long-term global warming.
“It actually was happening,” Young says. “They couldn’t quite prove it, but now we sort of have the evidence.”
According to the researchers, natural conditions had favored renewed ice expansion over the preceding two millennia. However, by the 1960s, rising global temperatures had become sufficient to reverse that trend, overwhelming the natural processes that had supported glacial growth.
The findings suggest that human-driven climate change has interrupted a long-term pattern of ice expansion, although this does not establish that a full continental-scale ice age was imminent during the 1970s.
The researchers conclude that continued melting of the Laurentide Ice Sheet’s remaining ice could complicate efforts to reconstruct past glacial cycles and predict how future periods of glaciation might unfold.
The paper, “Climate Change Stopped the Next Ice Age,” appeared in Science on October 22, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.