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

Changing atmospheric CO2 concentration was the primary driver of early Cenozoic climate
Changing atmospheric CO2 concentration was the primary driver of early Cenozoic climate
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 (?11B) 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.
0028-0836
380-384
Anagnostou, Eleni
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John, Eleanor H.
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Edgar, Kirsty M.
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Foster, Gavin L.
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Ridgwell, Andy
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Inglis, Gordon N.
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Pancost, Richard D.
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Lunt, Daniel J.
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Pearson, Paul N.
76269a23-3411-45a1-bc81-b3a668ef1d13
Anagnostou, Eleni
4527c274-f765-44ce-89ab-0e437aa3d870
John, Eleanor H.
c3e52564-92af-4636-84ec-3732a6c1bc05
Edgar, Kirsty M.
c180d215-e9ee-4a79-8274-a1e8a300c07c
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Ridgwell, Andy
769cea5c-e033-456a-8b53-51dfa307dc35
Inglis, Gordon N.
d78ea396-b651-452f-bf6d-fe9d5008e4b1
Pancost, Richard D.
5914e19e-7777-4304-9fd8-86e2e9cfe8a1
Lunt, Daniel J.
931ecfb5-1f50-412c-8f01-a46d69b1f82f
Pearson, Paul N.
76269a23-3411-45a1-bc81-b3a668ef1d13

Anagnostou, Eleni, John, Eleanor H. and Edgar, Kirsty M. et al. (2016) Changing atmospheric CO2 concentration was the primary driver of early Cenozoic climate. Nature, 533 (7603), 380-384. (doi:10.1038/nature17423).

Record type: Article

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 (?11B) 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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Accepted/In Press date: 10 February 2016
e-pub ahead of print date: 25 April 2016
Published date: 19 May 2016
Organisations: Geochemistry

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Local EPrints ID: 393509
URI: https://eprints.soton.ac.uk/id/eprint/393509
ISSN: 0028-0836
PURE UUID: 5dd6a625-99cd-48e6-b330-6508fb4decdd
ORCID for Gavin L. Foster: ORCID iD orcid.org/0000-0003-3688-9668

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Date deposited: 29 Apr 2016 15:35
Last modified: 07 Jun 2019 00:32

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Contributors

Author: Eleni Anagnostou
Author: Eleanor H. John
Author: Kirsty M. Edgar
Author: Gavin L. Foster ORCID iD
Author: Andy Ridgwell
Author: Gordon N. Inglis
Author: Richard D. Pancost
Author: Daniel J. Lunt
Author: Paul N. Pearson

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