Global warming interrupted a glacial period that had already begun

Columbia Climate School researchers used carbon-14 ages of vegetation preserved beneath the Barnes Ice Cap and nearby small ice caps on Baffin Island to reconstruct changes in the last remnant of the Laurentide Ice Sheet. Evidence indicates it reached a minimum about 3,000 years ago and began expanding again about 2,000 years ago, which the authors interpret as the start of the next glacial period. Around 1960, warmer summers made ice loss exceed winter accumulation and reversed the advance. Without that reversal, the authors estimate a continent-scale ice sheet would still have taken roughly 30,000 years to form. The Delaware-sized Barnes Ice Cap may disappear within coming centuries. The interpretation challenges the convention that a glacial period begins only after continental ice forms and still requires testing against other ice records and models.