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Changing atmospheric CO2 concentration was the primary driver of early Cenozoic climate

Nature volume 533, pages 380384 (19 May 2016) | Download Citation

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Abstract

The Early Eocene Climate Optimum (EECO, which occurred about 51 to 53 million years ago)1, was the warmest interval of the past 65 million years, with mean annual surface air temperature over ten degrees Celsius warmer than during the pre-industrial period2,3,4. Subsequent global cooling in the middle and late Eocene epoch, especially at high latitudes, eventually led to continental ice sheet development in Antarctica in the early Oligocene epoch (about 33.6 million years ago). However, existing estimates place atmospheric carbon dioxide (CO2) levels during the Eocene at 500–3,000 parts per million5,6,7, and in the absence of tighter constraints carbon–climate interactions over this interval remain uncertain. Here we use recent analytical and methodological developments8,9,10,11 to generate a new high-fidelity record of CO2 concentrations using the boron isotope (δ11B) composition of well preserved planktonic foraminifera from the Tanzania Drilling Project, revising previous estimates6. Although species-level uncertainties make absolute values difficult to constrain, CO2 concentrations during the EECO were around 1,400 parts per million. The relative decline in CO2 concentration through the Eocene is more robustly constrained at about fifty per cent, with a further decline into the Oligocene12. Provided the latitudinal dependency of sea surface temperature change for a given climate forcing in the Eocene was similar to that of the late Quaternary period13, this CO2 decline was sufficient to drive the well documented high- and low-latitude cooling that occurred through the Eocene14. Once the change in global temperature between the pre-industrial period and the Eocene caused by the action of all known slow feedbacks (apart from those associated with the carbon cycle) is removed2,3,4, both the EECO and the late Eocene exhibit an equilibrium climate sensitivity relative to the pre-industrial period of 2.1 to 4.6 degrees Celsius per CO2 doubling (66 per cent confidence), which is similar to the canonical range (1.5 to 4.5 degrees Celsius15), indicating that a large fraction of the warmth of the early Eocene greenhouse was driven by increased CO2 concentrations, and that climate sensitivity was relatively constant throughout this period.

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Change history

  • 19 May 2016

    The present address for author E.H.J. was amended.

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Acknowledgements

Financial support was provided by NERC grants (NE/H017356/1 and NE/I005595/1 to G.L.F. and P.N.P.) and by a NERC Post Doctoral Research Fellowship (NE/H016457/1 to K.M.E.). G.N.I. thanks the UK NERC for supporting his PhD studentship (via NE/I005595/1) and R.D.P. acknowledges the Royal Society Wolfson Research Merit Award. R.D.P. and G.N.I. also acknowledge the Advanced ERC Grant T-GRES (340923). We thank the Tanzania Petroleum Development Corporation, the Tanzania Commission for Science and Technology and the Tanzania Drilling Project field team for support. We also acknowledge A. Milton and S. Nederbraght for technical assistance, and we are grateful to M. Huber for discussions on drivers of Eocene warmth.

Author information

Author notes

    • Eleanor H. John
    •  & Kirsty M. Edgar

    Present addresses: School of Geography, Earth Science and Environment, University of the South Pacific, Suva, Fiji (E.H.J.); School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK (K.M.E.).

Affiliations

  1. Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton Waterfront Campus, Southampton SO14 3ZH, UK

    • Eleni Anagnostou
    •  & Gavin L. Foster
  2. School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff CF10 3AT, UK

    • Eleanor H. John
    • , Kirsty M. Edgar
    •  & Paul N. Pearson
  3. School of Earth Sciences, Bristol University, Bristol BS8 1RJ, UK

    • Kirsty M. Edgar
  4. School of Geographical Sciences, Bristol University, Bristol BS8 1SS, UK

    • Andy Ridgwell
    •  & Daniel J. Lunt
  5. Department of Earth Sciences, University of California, Riverside, California 92521, USA

    • Andy Ridgwell
    •  & Daniel J. Lunt
  6. Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK

    • Gordon N. Inglis
    •  & Richard D. Pancost
  7. Cabot Institute, University of Bristol, Bristol BS8 1UJ, UK

    • Gordon N. Inglis
    •  & Richard D. Pancost

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Contributions

E.A. conducted all boron isotope and trace element analyses, performed calculations, and drafted the manuscript. E.H.J. and K.M.E. prepared foraminifer samples and conducted the stable isotope analysis. P.N.P. led the fieldwork, performed the taxonomy and prepared foraminifer samples. A.R. provided cGENIE model results. P.N.P. and G.L.F. designed the study and all authors discussed the results and contributed to the final text.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Eleni Anagnostou.

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https://doi.org/10.1038/nature17423

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