Around 2,000 years ago, the Arctic ice sheet, a remnant of the last ice age, began to change. After retreating for thousands of years, it slowly started to grow again. A new glacial period was returning. However, this process was short-lived in geological terms, as summer temperatures had risen so much by the 1960s that the ice began to shrink once more. Put simply, human-caused global warming halted the onset of a new glacial period.
This is described in a new study by geochemists at Columbia Climate School. “It was just getting started, everything was proceeding as expected, the next glaciation was supposed to happen – and yet it stopped,” said Nicolás Young, who was involved in the research. “It’s a very clear example of how we have disrupted this system,” he added.
Technically speaking, we are still living in an ice age – the Late Cenozoic Ice Age – which began around 34 million years ago. Within this ice age, colder glacial periods alternate with warmer interglacial periods, including the one we are currently experiencing. What people commonly refer to as an “ice age” is usually a glacial period. The last glacial period ended around 11,700 years ago.
Young and his colleagues studied the Laurentide region of the Canadian Shield. Between 95,000 and 20,000 years ago, much of this area was covered by an ice sheet that reached a thickness of up to 3.2 kilometres in many places. Today, only an ice cap on Baffin Island remains. The researchers wanted to understand how the Laurentide Ice Sheet had changed in size over the past 2.6 million years.
The researchers faced a task almost as daunting as the legendary twelve labours of Hercules. Until now, mapping the movement of the ice sheet in detail had been virtually impossible. Geological traces of its movement are often erased over time, while human-induced changes to the landscape further complicate the work. This time, the researchers therefore turned to plants that had been preserved in the ice or released from it as the ice began to retreat again in the 20th century.
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The researchers then dated the collected samples using the well-established method of carbon-14 dating. This radioactive isotope decays at a predictable and therefore measurable rate after an organism dies. Using the vast amount of data collected, the scientists were able to reconstruct the history of the North American ice sheet.
The study revealed that the Laurentide Ice Sheet reached its smallest extent around 3,000 years ago. It then began to expand again approximately 2,000 years ago, as the climate cooled enough for ice to accumulate in the region. According to the study’s authors, this may have marked a turning point, signalling the beginning of a new glacial period.
Previous modelling studies had suggested that the next glaciation would not begin for thousands or even tens of thousands of years. However, Young and his colleagues argue that the onset of a new glacial period should be marked by the first renewed growth of an ice sheet, rather than waiting for the formation of vast continental ice sheets.
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According to the researchers, these new findings may offer some vindication to climatologists who suggested in the mid-20th century that a new ice age was approaching. “It really was happening,” Young emphasised. “They couldn’t fully prove it at the time, but now we have some evidence,” he added.
The changes now described by scientists were extremely slow. It would have taken hundreds of years for their effects to become noticeable, and around 30,000 years for the Canadian ice sheet to return to its former maximum extent.
However, as mentioned earlier, another factor emerged in the 1960s, ultimately outweighing the cooling trend. This was global warming caused by greenhouse gas emissions from burning fossil fuels. As a result, ice accumulation quickly came to a halt, and the ice sheet began to retreat instead. If the climate develops as projected, the remaining ice in Canada could disappear entirely within a few centuries.
Reference to the study (in English)
An article written by Tomáš Karlík (CT), initially published on 2 November 2026, 13:00 (CET)