Laurentide Ice Sheet began growing again before modern warming reversed its remnant's course
A new study traces renewed ice growth about 2,000 years ago and retreat at the Barnes Ice Cap since the 1960s, raising questions about when a glacial period begins.
The Laurentide Ice Sheet began growing again about 2,000 years ago, according to a study published in Science in 2026, before warming reversed the course of its surviving remnant, the Barnes Ice Cap on Canada's Baffin Island, by the 1960s. The findings bear on when scientists consider a glacial period to have begun, although the study's authors use a definition that differs from earlier model-based expectations.
How researchers traced the Laurentide Ice Sheet's growth
The Laurentide once covered much of Canada and the northern United States. The Barnes Ice Cap is its last surviving remnant. Researchers studied vegetation preserved beneath the cap and smaller ice caps that recently melted in the region. Dating that vegetation helped them reconstruct when the advancing ice covered plants, building a timeline of changes along its margin.
The team estimates that the Laurentide reached its smallest extent about 3,000 years ago and began expanding again roughly 2,000 years ago. Wired reported a separate measurement from exposed rocks near the Barnes Ice Cap: using beryllium-10, the researchers estimated that the cap first reached roughly its modern size about 3,600 years ago. The measurements describe different points in the ice's history.
Why the study calls renewed growth a glacial beginning
Nicolás E. Young and his colleagues argue that renewed ice-sheet growth should mark the beginning of a glacial period, even before a vast continental sheet forms. Columbia Climate School's account, republished by Phys.org, says earlier model-based studies had placed the next glaciation thousands or tens of thousands of years in the future. Under the scenario described by Young, cooling would have taken thousands of years to become noticeable and about 30,000 years for the Laurentide to regain its former continental reach.
That proposed starting point does not mean a continent-spanning ice sheet had returned. Meredith Kelly, a Dartmouth earth scientist quoted by Wired, called the ice-cap data strong but said comparisons with other sites would help establish how widely the pattern reflected a move toward glaciation. The mechanisms that initiate glacial periods also need further study, Wired reported.
What happened to the Barnes Ice Cap
By the 1960s, the Barnes Ice Cap was losing more ice in summer than it gained in winter, according to the Columbia Climate School account. Wired reported that historical aerial photographs show its renewed retreat and that its edges have receded by an average of four metres a year since the 1980s. The change occurred as carbon emissions rose and human-caused warming drove ice loss worldwide.
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Sources and context
- A New Ice Age Was Beginning. Then Humans Started Burning Fossil FuelsWired
- Global warming may have halted an emerging ice age, study suggestsColumbia Climate School, republished by Phys.org
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