A remnant of the ancient North American glacier system was expanding for two millennia before modern greenhouse gas emissions abruptly stopped its growth around 1960, effectively cutting short the infancy of Earth’s next ice age, according to research published in the journal Science.
The study focused on the Barnes Ice Cap, a Delaware-sized dome resting on Baffin Island in the Canadian territory of Nunavut. The glacier is the sole surviving fragment of the Laurentide Ice Sheet, which blanketed nearly a third of North America during the Pleistocene epoch, reaching depths of up to two miles from the Arctic Circle down into Illinois.
Preserved Clocks in the Tundra
Glaciers typically crush and grind down the terrain beneath them as they advance, destroying geological records. However, the Barnes Ice Cap remains frozen solid to the bedrock, meaning it functioned like a natural freezer that encased plants without scraping them away, researchers reported.
By collecting and radiocarbon dating 88 samples of long-dead mosses revealed as the ice retreated between 200 and 800 meters from 1960 to 2022, scientists mapped when the glacier crept outward. They paired that botanical data with tests of beryllium-10, a rare isotope formed by cosmic radiation in rocks, from 35 boulder and bedrock samples.
The rocks revealed that the ancient ice reached a minimum footprint roughly 3,500 years ago during the warm Holocene epoch. Then, about 2,000 years ago, shifting orbital conditions triggered cooler summers in the Northern Hemisphere, prompting the ice to expand across the landscape, Columbia University geochemist and lead author Nicolás Young told CNN.
“It was just getting started, everything was normal, the next glaciation was about to happen — and yet it stopped,” Young said, noting that summer heating driven by emissions since the mid-20th century overturned the natural trend.
Debate Over What Defines an Ice Age
Atmospheric greenhouse gases grew significantly after the start of the Industrial Revolution around 1750, peaking past preindustrial benchmarks by 1960. Since that time, the ice cap has experienced a negative mass balance, melting faster in summer months than snow can replenish in winter and losing its snow-accumulation zone completely since 2010.
The findings have drawn interest and debate from outside researchers across the paleoclimate community.
Meredith Kelly, an earth sciences professor at Dartmouth College, praised the project’s novel use of plant radiocarbon dating to recreate glacial movements, telling CNN that additional work comparing glaciers in other parts of the world would clarify how widely the phenomenon unfolded.
Other scientists expressed skepticism about calling the ice cap’s growth the definitive start of a global ice age. Andrey Ganopolski, a physicist at the Potsdam Institute for Climate Impact Research who previously modeled orbital cycles, argued that the growth of a single regional ice cap is insufficient to prove a planetary glacial cycle had officially commenced.
Long-Term Consequences
Young emphasized that the findings should not be viewed as global warming doing humanity a favor. Natural glaciations develop over thousands of years and would not have altered human society for millennia.
Instead, researchers pointed out that current warming profiles suggest the Barnes Ice Cap itself will ultimately melt away completely under sustained emissions, erasing the last physical vestige of North America’s ancient ice sheet and delaying future natural glacial cycles indefinitely.
