Barnes Ice Cap study traces centuries of growth before warming reversed it

Plants preserved beneath the ice

Canada’s Barnes Ice Cap expanded for at least a millennium before human-driven warming pushed it into retreat around 1960, according to a study described by Columbia University and CU Boulder on October 22. The research appeared in Science.

The evidence comes from land ice on Baffin Island in Nunavut, rather than a reconstruction of all Arctic sea ice. Barnes is a surviving remnant of the Laurentide Ice Sheet that once covered much of North America.

Researchers dated dead vegetation emerging from the retreating margin. Because the ice is frozen to the ground, it can preserve plants instead of grinding them away. Radiocarbon measurements indicate when advancing ice buried and killed them.

A thousand-year record and a broader reconstruction

CU Boulder describes direct evidence of growth extending back at least 1,000 years. Columbia places renewed expansion roughly 2,000 years ago using evidence from Barnes and nearby smaller ice caps. These describe different parts of the reconstruction, rather than interchangeable dates from a single sample.

The team attributes the eventual reversal to greenhouse warming overcoming the cooling influence of changes in Earth’s orbit. By the 1960s, summer losses exceeded winter accumulation, Columbia’s account says.

What the “ice age” claim means

The authors propose counting the first renewed ice-sheet growth as the onset of a glacial period, rather than waiting for continental-scale ice sheets to form. Columbia notes that this challenges model-based estimates placing the next glaciation thousands or tens of thousands of years ahead.

That interpretation does not establish that a continent-spanning freeze was imminent. Columbia explains that large-scale ice-sheet growth would have taken many thousands of years. It also says researchers cannot specify when another glaciation might occur with elevated greenhouse gas concentrations.