Radiocarbon-Dated Plants Show Earth's Next Ice Age Began 2,000 Years Ago, Then Stalled
A Science study of Baffin Island's Barnes Ice Cap finds ice was regrowing until warming in the 1960s reversed it. The lead author says humans have "jolted the system."
Earth may have been about 2,000 years into its next glacial period before human-caused warming stopped it, according to a study in the journal Science. Researchers at Columbia University's Lamont-Doherty Earth Observatory dated plants buried under Canada's Barnes Ice Cap and concluded that the last remnant of the great Laurentide Ice Sheet began regrowing about 2,000 years ago, until warming in the 1960s reversed it.
The Laurentide Ice Sheet covered much of Canada and the northern United States from about 95,000 to 20,000 years ago. At its peak it stretched from above the Arctic Circle to Illinois, with ice more than 3.2 kilometers, or 2 miles, thick in places. The Barnes Ice Cap, on Baffin Island in Nunavut and about the size of Delaware, is what is left of it.
The team, led by geochemist Nicolás E. Young and Joerg Schaefer, used the ice cap's unusual properties. It is frozen to its bedrock and does not slide, so it preserved plants that grew when it was smaller. As the ice has retreated since 1960, it has exposed those plants. Carbon-14 dating of them gave a timeline of the ice margin's advance. The researchers combined the results with data from smaller ice caps in the region that have recently melted.
The picture that emerged is that the Laurentide reached its minimum size about 3,000 years ago and began re-expanding about 2,000 years ago, when the climate turned cold enough for ice to accumulate. The authors argue this marks the start of Earth's next glacial period. That challenges model-based studies that predicted such a start was delayed by thousands to tens of thousands of years.
The paper, titled "Late Holocene re-expansion of the Laurentide Ice Sheet," says the process was reversed by the 1960s, when summer melt on the Barnes Ice Cap began to exceed winter accumulation. Young said regaining continental-scale mass would have taken about 30,000 years, though the cooling was already underway. "It's a very powerful example of how we have jolted the system," he said. "What has been an extremely natural and predictable phenomenon is now gone."
Models project that the Barnes Ice Cap will melt completely within the next few centuries. Because the Laurentide acted as a nucleation point for ice growth during past cooling, its loss could change how future glaciations begin.
The findings echo claims made in the 1970s that a new ice age was imminent, which Young says the new evidence supports in a limited sense: the cooling trend was real, but it has been overtaken. The result does not mean an ice age is coming, since the ice cap is shrinking, but it recasts today's warming as interrupting a slow natural cycle rather than merely adding to a stable climate.
