Transient Middle Eocene Atmospheric CO2 and Temperature Variations

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Science  05 Nov 2010:
Vol. 330, Issue 6005, pp. 819-821
DOI: 10.1126/science.1193654

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The Dependable Warmer

During the middle of the Eocene, about 40 million years ago, a transient warming event interrupted the long-term cooling trend that had been in progress for the previous 10 million years. Bijl et al. (p. 819; see the Perspective by Pearson) constructed records of sea surface temperature and atmospheric CO2 concentrations across the warming period. It appears that vast amounts of CO2 were injected into the atmosphere, and a sea surface temperature increase of as much a 6°C accompanied the atmospheric CO2 rise.


The long-term warmth of the Eocene (~56 to 34 million years ago) is commonly associated with elevated partial pressure of atmospheric carbon dioxide (pCO2). However, a direct relationship between the two has not been established for short-term climate perturbations. We reconstructed changes in both pCO2 and temperature over an episode of transient global warming called the Middle Eocene Climatic Optimum (MECO; ~40 million years ago). Organic molecular paleothermometry indicates a warming of southwest Pacific sea surface temperatures (SSTs) by 3° to 6°C. Reconstructions of pCO2 indicate a concomitant increase by a factor of 2 to 3. The marked consistency between SST and pCO2 trends during the MECO suggests that elevated pCO2 played a major role in global warming during the MECO.

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