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September 15, 2009

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Scientists link carbon dioxide to ice sheets

A TEAM of scientists studying rock samples in Africa has shown a strong link between falling carbon dioxide levels and the formation of Antarctic ice sheets 34 million years ago.

The results are the first to make the link, underpinning computer climate models that predict both the creation of ice sheets when carbon dioxide levels fall and the melting of ice caps when carbon dioxide levels rise.

The team, from Cardiff, Bristol and Texas A&M Universities, spent weeks in the African bush in Tanzania with an armed guard to protect them from lions to extract samples of tiny fossils that could reveal carbon dioxide levels in the atmosphere 34 million years ago.

Levels of carbon dioxide, the main greenhouse gas, mysteriously fell during this time in an event called the Eocene-Oligocene climate transition.

"This was the biggest climate switch since the extinction of the dinosaurs 65 million years ago," said co-author Bridget Wade from Texas A&M University.

The study reconstructed carbon dioxide levels around this period, showing a dip around the time ice sheets in Antarctica started to form.

Carbon dioxide levels were around 750 parts per million, about double current levels.

"There are no samples of air from that age that we can measure, so you need to find something you can measure that would have responded to the atmospheric carbon dioxide," Paul Pearson of Cardiff University said.

Pearson, Wade and Gavin Foster from the University of Bristol gathered sediment samples in the Tanzanian village of Stakishari where there are deposits of well-preserved microfossils that can reveal past carbon dioxide levels.

The results were published online in the journal Nature.


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