Ice age end was accelerated by CO₂

A new global study of ice core samples and underwater sediment suggests that rising atmospheric CO₂ preceded the ending of the last Ice Age – not the other way around.

One of the favourite rhetorical devices of the climate change denier is to invert cause-and-effect – in other words, the carbon rise around the end of the last Ice Age happened as a result of the warming, not the other way around.

The latest study, published in Nature, could help put paid to this: in most of the 80 sites from which samples were taken, the scientists say, it’s clear that rising CO₂ predated the “big melt”.

Over a period of 7,000 years, the scientists say, the atmospheric concentration of CO₂ rose from 180 parts per million to 260 ppm. While the initial cause of the end of the Ice Age was a change in the “wobble” of Earth’s axis, the researchers believe the process was then accelerated by the CO₂, possibly released from the warmer oceans.

As Christian Science Monitor reports, the only place in which the current study finds CO₂ rises followed warming was in Antarctica: elsewhere, the rising carbon precedes accelerating warming.

As noted in the abstract, that difference can be associated with ocean currents: “Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments.”

“An antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO2 concentrations is an explanation for much of the temperature change at the end of the most recent ice age,” the abstract states.

It’s worth noting that the 260 ppm reached at the end of the Ice Age – sufficient to “deglaciate” huge amounts of the world – is far below today’s figure, which is closing in on 400 ppm. Lead author of the study, Jeremy Shakun, says we’re likely to end up carrying a further 100 ppm by the end of the century.

Shakun, of Oregon State University, collaborated with researchers from Harvard University and other institutions in America, China and France to conduct the study. ®