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

Erin L. McClymont, Heather L. Ford, Sze Ling Ho, Julia C. Tindall, Alan M. Haywood, Montserrat Alonso-Garcia, Ian Bailey, Melissa A. Berke, Kate Littler, Molly O. Patterson, Benjamin Petrick, Francien Peterse, A. Christina Ravelo, Bjorg Risebrobakken, Stijn De Schepper, George E.A. Swann, Kaustubh Thirumalai, Jessica E. Tierney, Carolien Van Der Weijst, Sarah WhiteAyako Abe-Ouchi, Michiel L.J. Baatsen, Esther C. Brady, Wing Le Chan, Deepak Chandan, Ran Feng, Chuncheng Guo, Anna S. Von Der Heydt, Stephen Hunter, Xiangyi Li, Gerrit Lohmann, Kerim H. Nisancioglu, Bette L. Otto-Bliesner, W. Richard Peltier, Christian Stepanek, Zhongshi Zhang

Research output: Contribution to journalArticlepeer-review

50 Scopus citations


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 2:3 C for the combined proxy data (foraminifera Mg=Ca and alkenones), or by 3:2 3.4 C (alkenones only). Compared to the preindustrial 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 seasurface 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.

Original languageEnglish (US)
Pages (from-to)1599-1615
Number of pages17
JournalClimate of the Past
Issue number4
StatePublished - Aug 27 2020

ASJC Scopus subject areas

  • Global and Planetary Change
  • Stratigraphy
  • Palaeontology


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