The Next Ice Age Began 2,000 Years Ago. Then, in 1960, Humans Abruptly Ended It.

3 min readResearchers at Columbia University have pinpointed the summer of 1960 as the moment when a new glacial period, which had already begun, started melting away. They said the blame rests squarely on humans and the surge in greenhouse gases.In a new study published in the journal Science, the researchers wrote that the newest glacial period (often colloquially called an ice age) began 2,000 years ago, even though it would have taken about 30,000 years for anyone to really notice. Human activity cut it short in 1960.“It was just getting started, everything was normal, the next glaciation was about to happen—and yet it stopped,” Nicolas Young, a geochemist at the Columbia Climate School, said in a statement from Columbia University. “It’s a very powerful example of how we have jolted the system.”To gather their data, the team studied what remains of the Laurentide Ice Sheet. At its peak roughly 20,000 years ago, the ice sheet stretched from the Arctic Circle down to Illinois and was two miles thick in places. It shrank to its smallest size about 3,000 years ago, then started growing again about 2,000 years ago.“People always say that it disappeared, but that’s not true,” Young said of the ice sheet. He noted that a piece of it survives today as the Barnes Ice Cap on Baffin Island in the Canadian territory of Nunavut, and that this remnant is still about the size of Delaware. Because the ice cap is frozen directly to the bedrock beneath it, it doesn’t slide, so it preserves the vegetation underneath instead of scraping it away. When the ice expands, it entombs the plants it covers. When it recedes, it exposes them again, allowing the team to sample the moss and date it using radiocarbon dating.“If you do this enough times, you can actually develop a timeline of that ice margin systematically advancing over plants,” Young said. “You’re actually tracking the expansion of that ice margin.”That timeline is critical, according to Joerg Schaefer, also a Columbia climate geochemist. “We have a decent understanding of how this enormous ice sheet grew and disappeared over thousands of years from proxy records, but catching the start of this process with direct observations is new,” Schaefer said. “Our approach helped us see the first steps of ice-sheet growth preserved in the landscape. It gave us a rare opportunity to understand how re-glaciation begins and how the Laurentide Ice Sheet reforms.”Technically, Earth has been in the Late Cenozoic Ice Age for about 34 million years, the researchers said. Within that span, the planet swings between glacial periods and warmer interglacial periods, and conventionally we have been in an interglacial since the last glacial period ended roughly 11,700 years ago. The new research challenges that framework by arguing that the first renewed growth of an ice sheet equals the start of a glacial period, “marking the onset of the next glaciation.” That period didn’t last long, however. The ice cap reached its maximum extent around 1960, when summer warming caused a “negative mass balance, ice margin recession, and the termination of the next glaciation.”In other words, Earth’s climate had warmed enough that the Barnes Ice Cap lost more ice in the summer of 1960 than it gained the previous winter, effectively ending the next glaciation. “The demise of the next glaciation, despite the ongoing decline in summer insolation, illustrates the influence of anomalous greenhouse gas forcing on climate,” the authors wrote.The team expects the ice cap to vanish within a few centuries. Without that icy foundation, it will be harder for new ice to build up. As a result, scientists can’t say when (or where) the next glaciation might occur, especially while greenhouse gas concentrations in the atmosphere remain high.Young described what the ice cap’s loss will mean: “That will be the true very last remains of the Laurentide, disappearing for good,” he said. “What has been an extremely natural and predictable phenomenon is now gone.”Watch Our Science VideosTim Newcomb is a journalist based in the Pacific Northwest. He covers stadiums, sneakers, gear, infrastructure, and more for a variety of publications, including Popular Mechanics. His favorite interviews have included sit-downs with Roger Federer in Switzerland, Kobe Bryant in Los Angeles, and Tinker Hatfield in Portland.