Did ‘Climate change stop the next ice age’, as these researchers claim?

An unusually extended interglacial has happened before: MIS 11 represents the longest and warmest interglacial interval of the last 500 kyr. In theory at least a repeat due to natural variation can’t be ruled out. Blaming humans now can only be an opinion, not a statement of fact. Note the curious case of the Arctic’s returning Odden ice tongue. (NB: In the headline, ‘ice age’ really means ‘glaciation’, as explained below).
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Two thousand years ago, the Arctic remnants of a once-vast ice sheet started to grow again, says EurekAlert.

It was the beginning of a new glacial period, more conversationally known as the next ice age—but by the 1960s, summer temperatures were already so high that the ice sheet started to shrink. In other words, global warming ended a period of glaciation that had already begun.

“It was just getting started, everything was normal, the next glaciation was about to happen—and yet it stopped,” says Nicolás Young, a geochemist at the Lamont-Doherty Earth Observatory, part of the Columbia Climate School. “It’s a very powerful example of how we have jolted the system.” [Talkshop comment – strong assertions need strong evidence]

In a new study published in the journal Science, Young, fellow Lamont geochemist Joerg Schaefer and their colleagues describe their research on the Laurentide Ice Sheet, which covered much of Canada and the northern United States from about 95,000 to 20,000 years ago. At its largest, it stretched from above the Arctic Circle to Illinois, and in places the ice was over two miles thick.

The last vestige of the Laurentide still survives as the Barnes Ice Cap, now a Delaware-sized ice cap located on central Baffin Island in the Canadian territory of Nunavut. “People always say that it disappeared, but that’s not true,” says Young. And while it’s known that the Laurentide has repeatedly expanded and retreated across North America since widespread, continental-scale glaciation began about 2.6 million years ago, Young’s team wanted to know whether it had ever shrunk even smaller than it is now and then regrown.

(A note on terminology: Technically we are still living in an ice age–the Late Cenozoic Ice Age–which started about 34 million years ago. Within it, colder glacial periods alternate with warmer interglacial ones, including the one we live in now. What people casually call an “ice age” is usually a glacial period. The last glacial period ended about 11,700 years ago.)
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By combining analyses of vegetation preserved beneath the Barnes Ice Cap and smaller recently-melted ice caps in the region, the researchers pieced together a climate history. The Laurentide reached its minimum dimensions about 3,000 years ago, then started re-expanding about 2,000 years ago when the climate became cold enough for ice to accumulate.

The researchers argue that this inflection point should be considered the beginning of Earth’s next glacial period. This interpretation challenges prevailing ideas about when glacial periods begin.

Previous model-based studies have suggested that the next glaciation would not begin for thousands or even tens of thousands of years. Young and his colleagues argue that the first renewed growth of an ice sheet should count as the beginning, rather than waiting until enormous continental ice sheets have formed.

Full news release here.
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Image: Greenland ice sheet (east coast) [credit: Hannes Grobe @ Wikipedia]