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CO2 to blame in ancient global warming event

This picture is of a spliced drill core from the Southern Ocean. Much multidisciplinary research focuses on reconstructing fossil environments using information from the fossil ocean floor.
Image courtesy of the Shipboard Scientific Party of IODP Leg 318.

Increased amounts of carbon dioxide in the atmosphere played a major role in global warming about 40 million years ago, during the Middle Eocene period, a new study reports.

This research appears in the 5 November issue of the journal Science.

While climate conditions have since changed, most notably the growth of permanent ice sheets at the North and South poles, the findings may help scientists forecast how carbon dioxide will affect global warming in the future.

It's well known that some 40 million years ago during the middle of the Eocene period the Earth warmed up for a short time, interrupting the long-term cooling that had been in progress for the past 10 million years.

Using a technique called organic molecular paleothermometry, Peter Bijl from Utrecht University in the Netherlands and an international team of researchers patched together records of sea surface temperature and atmospheric carbon dioxide concentrations across the Middle Eocene period from plankton fossils.

Electron microscopic picture of microfossils found in the drill cores. By studying the remains of such marine plankton, scientists gain an accurate perspective of past climate change. Earlier, members of the same research team showed that the Arctic Ocean was colonized by similar types of tropical plankton. Scale bar is 20 micrometer, or 0.02 millimeter.
Image courtesy of Appy Sluijs.

The researchers found that during this interval of short-term warming, vast amounts of carbon dioxide were injected into the atmosphere, and that a sea surface temperature increase of as much as 6 degrees Celsius accompanied the atmospheric carbon dioxide rise.

Such a causal link between rising carbon dioxide levels and sea temperatures is consistent with recent models that predict sea surface temperature increases of 2 to 5 degrees Celsius for a doubling of carbon dioxide.