Human-caused warming reversed renewed growth of Canada’s Barnes Ice Cap

The Barnes Ice Cap in northern Canada began growing again about 2,000 years ago, after reaching a smaller size.

It is the last remnant of the Laurentide Ice Sheet, which once covered much of Canada and the northern United States.

Researchers reconstructed its past by dating plants buried under the ice and measuring an isotope in exposed rocks.

The ice cap kept growing until around 1960, when rising summer temperatures tipped the balance toward melting.

By 2022, its edge had retreated about 200 to 800 metres, and the study’s authors link the change mainly to human-caused warming.

They interpret the earlier growth as the start of a new ice age, but that view depends on how an ice age is defined; other researchers say the conclusion needs more comparison with glaciers elsewhere.

The findings show greenhouse gas emissions can override natural climate shifts, though the study does not say when another ice age would otherwise begin.

Models suggest the Barnes Ice Cap could disappear in the coming centuries, but how many future ice-age cycles are affected depends on human choices and future emissions.