Human greenhouse gas emissions reversed the onset of a new ice age that began approximately 2,000 years ago, according to a study published in the journal Science. Researchers examining the Barnes Ice Cap on Baffin Island in Canada’s Nunavut territory found that the Delaware-sized ice dome began expanding around 2,000 years ago, marking the start of a new glacial period that was subsequently halted by mid-20th-century warming.
Tracking the Laurentide Ice Sheet Remnant
The study focuses on the Barnes Ice Cap, which is the last surviving remnant of the massive Laurentide Ice Sheet. During the Pleistocene epoch, this ice sheet covered a great deal of the northern US and Canada, stretching from the Arctic Circle down to Illinois with ice up to 3 kilometers thick. As the current interglacial period—the Holocene—progressed after beginning 11,700 years ago, the ice sheet shrank significantly. By 3,600 years ago, it reached a minimum size before beginning to regrow around 2,000 years ago in response to cooler regional temperatures.
To reconstruct this timeline, researchers utilized atomic dating methods on in-situ evidence. They analyzed cosmogenic beryllium-10 isotopes in surrounding rocks to measure how long stones had been shielded by ice or exposed to cosmic radiation. Additionally, they performed radiocarbon dating on vegetation and mosses that had been entombed by the advancing ice cap and were only recently revealed as the ice retreated. “We can actually track the expansion of the ice margin as it’s progressively covering mosses and killing (them),” said Nicolás Young, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory and the study’s lead author, speaking with CNN.
Industrial Warming Versus Natural Glaciation
The expanding ice cap kept growing until the late 1950s. Shortly thereafter, warming from rising greenhouse gas emissions reversed its growth trajectory. Rising summer temperatures pushed the ice cap into a negative mass balance, causing it to melt faster in warm months than winter snows could replenish. Climate pollution has “essentially overpowered” the natural orbital mechanisms that “want to make that region cool,” Young said.
Co-author Joerg Schaefer, a geochemist at Columbia University, noted that the approach allowed researchers to observe the initial stages of ice-sheet growth preserved directly in the landscape. “It gave us a rare opportunity to understand how re-glaciation begins and how the Laurentide Ice Sheet re-forms,” Schaefer said in a statement.
Scientific Debate Over Glacial Inception
The interpretation that an ice age had actively begun has drawn debate within the paleoclimatology community. Andrey Ganopolski, a physicist at the Potsdam Institute for Climate Impact Research, argued that the growth of the Barnes Ice Cap “is insufficient to support the conclusion that a new glacial cycle had already begun and was subsequently aborted.” Ganopolski previously authored a 2016 study concluding that human emissions would delay the next natural ice age by 50,000 years or so, and traditional climate models typically require massive ice sheets locking up several meters of global sea level before declaring a glacial inception.
Meredith Kelly, an earth sciences professor at Dartmouth College who was not involved with the study, praised the research for applying techniques including “novel radiocarbon dating of plants” to map the advance and retreat phases. Young and his co-authors maintain that waiting for colossal ice sheets misses the actual birth of a glacial period, arguing that the initial expansion of the Laurentide Ice Sheet remnants counts as the true onset of an ice age.
The findings also address historical speculation from the 1970s, when some scientists suggested Earth might be entering a new ice age. Instead of an imminent deep freeze, the study illustrates how profoundly human activity has altered geological norms. “Humans are now geologic agents capable of thwarting millions of years of natural glacial cycles and offsetting Earth’s climate for hundreds of thousands of years to come.”
