Researchers have found that carbon dioxide (CO2) levels are higher today than they have ever been in the last 2.1 million years.

In the study, Bärbel Hönisch, a geochemist at Lamont-Doherty Earth Observatory of Columbia University, and her colleagues reconstructed CO2 levels by analyzing the shells of single-celled plankton buried under the Atlantic Ocean, off the coast of Africa. By dating the shells and measuring their ratio of boron isotopes, they were able to estimate how much CO2 was in the air when the plankton were alive.

The study rules out the idea that a drop in CO2 was the cause of the earth’s ice ages growing longer and more intense some 850,000 years ago. But it confirms the idea that higher CO2 levels coincided with warmer intervals during the period.

By reconstructing atmospheric CO2 levels over the past 2.1 million years, the researchers were able to shed new light on its role in the earth’s cycles of cooling and warming.

This showed that peak CO2 levels over the last 2.1 million years averaged only 280 parts per million, while today, CO2 levels have gone 38% higher at 385 parts per million.

The study found that around 850,000 years ago, cycles of ice grew longer and more intense, but that the CO2 was flat during this transition and unlikely to have triggered the change. This debunks the theory that a drop in CO2 caused ice ages.

The findings of the study were published in the June 19 issue of the journal Science. Aside from Hönisch, the paper’s co-author is Garry Hemming, a researcher at Lamont-Doherty and Queens College. The study’s other authors are Jerry McManus, also at Lamont; David Archer at the University of Chicago; and Mark Siddall, at the University of Bristol, UK.


-  Katrice R. Jalbuena

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Sources:

¹ http://www.earth.columbia.edu/articles/view/2501
² http://www.earth.columbia.edu/sections/view/9