Yale-led team finds CO2 levels plunged as Antarctica froze

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This series of illustrations depicts the progression of ice over what is now called Antarctica during a roughly 80,000-year period about 34 million years ago. The white represents continental ice, the colors sea ice. A research team led by a Yale University scientist has found evidence that carbon dioxide levels in Earth’s atmosphere plunged prior to and during the initial icing of Antarctica. (Illustration credit: Robert M. DeConto)

A Yale University-led research team has found evidence that carbon dioxide levels in Earth’s atmosphere plunged prior to and during the initial icing of Antarctica, about 34 million years ago. The new findings provide further evidence of atmospheric carbon dioxide’s role as a major trigger of global climate change.

“CO2 is tracking global cooling at that time,” said Yale geochemist Mark Pagani, lead author of a paper published online Dec. 1 in the journal Science. “It’s important to demonstrate that there are obvious linkages between CO2 and climate change. It’s one more piece of evidence that CO2 is a primary lever on climate.”

As CO2 levels fell, average temperatures also fell and massive sheets of ice formed. The freezing of Antarctica, the fifth largest and southern-most of the continents, occurred an estimated 33.7 million years ago, as the Eocene epoch gave way to the Oligocene. Today 98 percent of Antarctica’s area is covered in ice; the other 2 percent is barren rock.

Pagani’s multidisciplinary, international team studied regional differences in CO2 estimates and trends across the Eocene-to-Oligocene climate transition, relying on measurements of molecules from algae at six ocean sites.

Collectively, the team’s estimates indicate that CO2 fell about 40 percent over a three-million-year period, which is consistent with theoretical model estimates for the threshold CO2 level required for rapid Antarctic icing.

“We conclude that the available evidence supports a fall in CO2 as a critical condition for global cooling and cryosphere evolution about 34 million years ago,” the authors write in the paper, noting this illustrates the fundamental link between greenhouse gases, ice sheets, and sea level.

The cryosphere is the frozen part of the Earth’s surface, including polar ice caps, continental ice sheets, sea ice and other forms of frozen water.

In addition to Pagani, the authors are Matthew Huber of Purdue University; Zhonghui Liu of The University of Hong Kong, in China; Steven M. Bohaty of the University of Southampton, in England; Jorijntje Henderiks of Uppsala University, in Sweden; Willem Sijp of University of New South Wales, in Australia; Srinath Krishnan of Yale; and Robert M. DeConto of the University of Massachusetts-Amherst.

Their research was supported by the Yale University Department of Geology and Geophysics, the National Science Foundation, NERC, and the Royal Swedish Academy of Sciences.

Science & Technology

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