Earth was slowly marching toward a new ice age for centuries until human greenhouse gas emissions abruptly disrupted the cycle in the mid-20th century, according to a study published in the journal Science.
Researchers analyzing ancient vegetation preserved beneath Canada’s Barnes Ice Cap found that Arctic ice had been expanding for as long as 2,000 years under the cooling influence of natural orbital variations. However, rapid increases in carbon pollution during the 1960s completely overwhelmed that natural trajectory, halting centuries of glacial growth and triggering a steep retreat, the University of Colorado Boulder reported.
Evidence Frozen in Time
Located on Baffin Island in northeastern Canada, the Delaware-sized Barnes Ice Cap is the sole surviving remnant of the Laurentide Ice Sheet, which blanketed Canada and parts of the northern United States during the previous ice age some 12,000 years ago. Unlike flowing glaciers that grind across terrain, the ice cap is frozen directly to the bedrock, keeping the underlying tundra vegetation undisturbed.
By collecting dead moss and shrubs emerging along the receding edges of the ice, scientists used radiocarbon dating to identify the exact moments the expanding ice buried and killed the plants. Using Beryllium-10 exposure dating on surrounding boulders, the researchers determined the sheet initially shrank to its current footprint about 3,600 years ago before natural planetary cycles prompted it to expand again around 2,000 years ago, according to WIRED.
“Modern retreat of this glacier has reversed 2,000 years of net expansion—that’s a pretty decent chunk of time,” said lead author Nicolás Young, a paleoclimatologist at Columbia University’s Lamont-Doherty Earth Observatory.
Halting a Natural Cycle
For millennia, shifts in Earth’s tilt and orbital path around the sun—known to researchers as Milankovitch cycles—have regulated transitions between freezing glacial epochs and warmer interglacial periods. The data indicated that Arctic ice reached its maximum modern footprint around 1960, precisely when rising greenhouse gas emissions counterbalanced the cooling effects of Earth’s orbit.
Historical aerial photographs show that since the 1980s, the margins of the Barnes Ice Cap have receded by an average of about four meters each year, WIRED reported. Study co-author Gifford Miller of the University of Colorado Boulder noted that early surveys conducted in the 1950s and 1960s mistakenly concluded the ice cap was naturally stable, capturing only a brief, unprecedented equilibrium right before industrial emissions gained dominance.
The study also sheds new light on scientific warnings issued during the 1970s. At the time, researchers noticed cooling conditions across the Arctic and alerted President Richard Nixon that a glaciation phase was potentially underway. While climate skeptics later pointed to those predictions to question modern climate science, Young stated the new evidence demonstrates that a natural glaciation was indeed beginning until carbon pollution disrupted it.
Next Steps in Glacial Research
Independent scientists say the research provides compelling evidence but emphasizes the need for wider validation. Meredith Kelly, a professor of earth sciences at Dartmouth who was not part of the research team, praised the study’s clarity while noting that scientists must compare the findings against other cold-region sites worldwide to map the precise mechanics that govern how ice sheets initiate growth.
