https://www.wired.com/story/ice-age-beginning-then-humans-started-burning-fossil-fuels/
Ancient plants reveal that the vestiges of the North American ice sheet started expanding a few thousand years ago, but that climate change caused it to reverse course.
By MOLLY TAFT – Wired Mag
Excerpt: Burning fossil fuels may have stopped the Earth from entering another ice age, a new study suggests. The research, published Thursday in the journal Science, uses samples of ancient vegetation and rock records to analyze the growth—and sudden retreat—of an ice cap that is the last vestige of an ice sheet that once covered much of North America.
The findings shows the Barnes Ice Cap, which covers parts of Canada’s Baffin Island, started growing a few thousand years ago before rapidly reversing course beginning in the 1960s as carbon pollution ramped up.
“A question that’s in the popular consciousness is, have we caused enough global warming to stop the next ice age from happening?” says Andrew Wickert, an associate professor of environmental science at the University of Minnesota Twin Cities, who was not involved in the research. The new research shows that “even as we were just starting to ramp up emissions, we’ve already done enough damage to cause the major North American ice sheet to already start retreating. That’s significant.”
The planet regularly goes through phases where ice extends down from the high latitudes—what we colloquially call “ice ages”—due to natural shifts in the Earth’s rotation and orbit, known as Milankovitch Cycles. Those are followed by interglacial periods where ice retreats toward the poles.
The last ice age ended 12,000 years ago. At its peak, what’s known as the Laurentide Ice Sheet covered all of Canada and extended as far south as New York and the Midwest. It retreated to form the Barnes Ice Cap, which covers an area the size of Delaware on Baffin Island.
Unlike glaciers, which can move, the Barnes Ice Cap is frozen to the bedrock, preserving the vegetal record of what grew around it under the ice. That quirk allowed the scientists leading the new study to glean information about how much it has grown—and shrank.
To determine when it first reached its modern size, they used an exposure dating technique to calculate roughly how long rocks several meters from the glacier’s edge had been exposed to the sky. Using measurements of Beryllium-10, an element that forms on the surface of exposed rock, the authors calculated that the ice sheet first reached the size it is today around 3,600 years ago.
The evidence presented in this paper, Young says, could also validate a decades-old hypothesis that has long been held up by climate deniers as “evidence” climate change is a hoax. In the early 1970s, scientists gathered for a meeting at Brown University to discuss hypotheses of when the next ice age might happen. (Young says that two of his coauthors on this paper were at that meeting.) The scientists concluded that a glaciation period was so imminent that they sent a warning letter to President Richard Nixon.
“I think this study actually helps show that scientists were right about a pending glaciation,” Young says. “
Media coverage of the meeting, as well as a colder period of weather in the 1970s, have long been pitched by climate deniers as “proof” that global warming isn’t actually happening. It very much is, though, and the new research actually adds to the evidence.
