Lessons from a high-CO2 world: An ocean view from ∼ 3 million years ago

A range of future climate scenarios are projected for high atmospheric CO2 concentrations, given uncertainties over future human actions as well as potential environmental and climatic feedbacks. The geological record offers an opportunity to understand climate system response to a range of forcings and feedbacks which operate over multiple temporal and spatial scales. Here, we examine a single interglacial during the late Pliocene (KM5c, ca. 3.205 +/- 0.01 Ma) when atmospheric CO2 exceeded pre-industrial concentrations, but were similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were almost identical to today, we are able to focus on equilibrium climate system response to modern and near-future CO2. Using proxy data from 32 sites, we demonstrate that global mean sea-surface temperatures were warmer than pre-industrial values, by similar to 2.3 degrees C for the combined proxy data (foraminifera Mg/Ca and alkenones), or by similar to 3.2-3.4 degrees C (alkenones only). Compared to the pre-industrial period, reduced meridional gradients and enhanced warming in the North Atlantic are consistently reconstructed. There is broad agreement between data and models at the global scale, with regional differences reflecting ocean circulation and/or proxy signals. An uneven distribution of proxy data in time and space does, however, add uncertainty to our anomaly calculations. The reconstructed global mean sea-surface temperature anomaly for KM5c is warmer than all but three of the PlioMIP2 model outputs, and the reconstructed North Atlantic data tend to align with the warmest KM5c model values. Our results demonstrate that even under low-CO2 emission scenarios, surface ocean warming may be expected to exceed model projections and will be accentuated in the higher latitudes.

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Related Dataset #1 : Sea surface temperature anomalies for Pliocene interglacial KM5c (PlioVAR)
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Author McClymont, Erin L.
Ford, Heather L.
Ho, Sze Ling
Tindall, Julia C.
Haywood, Alan M.
Alonso-Garcia, Montserrat
Bailey, Ian
Berke, Melissa A.
Littler, Kate
Patterson, Molly O.
Petrick, Benjamin
Peterse, Francien
Ravelo, A. Christina
Risebrobakken, Bjørg
De Schepper, Stijn
Swann, George E. A.
Thirumalai, Kaustubh
Tierney, Jessica E.
van der Weijst, Carolien
White, Sarah
Abe-Ouchi, Ayako
Baatsen, Michiel L. J.
Brady, Esther C.
Chan, Wing-Le
Chandan, Deepak
Feng, Ran
Guo, Chuncheng
von der Heydt, Anna S.
Hunter, Stephen
Li, Xiangyi
Lohmann, Gerrit
Nisancioglu, Kerim H.
Otto-Bliesner, Bette L.
Peltier, W. Richard
Stepanek, Christian
Zhang, Zhongshi
Publisher UCAR/NCAR - Library
Publication Date 2020-08-27T00:00:00
Digital Object Identifier (DOI) Not Assigned
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Topic Category geoscientificInformation
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Metadata Date 2023-08-18T18:13:44.416258
Metadata Record Identifier edu.ucar.opensky::articles:23635
Metadata Language eng; USA
Suggested Citation McClymont, Erin L., Ford, Heather L., Ho, Sze Ling, Tindall, Julia C., Haywood, Alan M., Alonso-Garcia, Montserrat, Bailey, Ian, Berke, Melissa A., Littler, Kate, Patterson, Molly O., Petrick, Benjamin, Peterse, Francien, Ravelo, A. Christina, Risebrobakken, Bjørg, De Schepper, Stijn, Swann, George E. A., Thirumalai, Kaustubh, Tierney, Jessica E., van der Weijst, Carolien, White, Sarah, Abe-Ouchi, Ayako, Baatsen, Michiel L. J., Brady, Esther C., Chan, Wing-Le, Chandan, Deepak, Feng, Ran, Guo, Chuncheng, von der Heydt, Anna S., Hunter, Stephen, Li, Xiangyi, Lohmann, Gerrit, Nisancioglu, Kerim H., Otto-Bliesner, Bette L., Peltier, W. Richard, Stepanek, Christian, Zhang, Zhongshi. (2020). Lessons from a high-CO2 world: An ocean view from ∼ 3 million years ago. UCAR/NCAR - Library. http://n2t.net/ark:/85065/d7kd225c. Accessed 26 July 2025.

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