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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-161
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-161
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 09 Jan 2020

Submitted as: research article | 09 Jan 2020

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Lessons from a high CO2 world: an ocean view from ~ 3 million years ago

Erin L. McClymont1, Heather L. Ford2, Sze Ling Ho3, Julia C. Tindall4, Alan M. Haywood4, Montserrat Alonso-Garcia5,6, Ian Bailey7, Melissa A. Berke8, Kate Littler7, Molly Patterson9, Benjamin Petrick10, Francien Peterse11, A. Christina Ravelo12, Bjørg Risebrobakken13, Stijn De Schepper13, George E. A. Swann14, Kaustubh Thirumalai15, Jessica E. Tierney15, Carolien van der Weijst11, and Sarah White16 Erin L. McClymont et al.
  • 1Department of Geography, Durham University, Durham, DH1 3LE, UK
  • 2School of Geography, Queen Mary University of London, London, UK
  • 3Institute of Oceanography, National Taiwan University, 10617 Taipei, Taiwan
  • 4School of Earth and Environment, University of Leeds, Leeds, LS29JT, UK
  • 5Department of Geology, University of Salamanca, Salamanca, Spain
  • 6CCMAR, Universidade do Algarve, 8005-139 Faro, Portugal
  • 7Camborne School of Mines & Environment and Sustainability Institute, University of Exeter, Exeter, UK
  • 8Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame IN 46656, USA
  • 9Department of Geological Sciences and Environmental Studies, Binghamton University SUNY, 4400 Vestal Pkwy E, Binghamton, New York, USA
  • 10Max Planck Institute for Chemistry, Climate Geochemistry Department, 55128 Mainz, German
  • 11Department of Earth Sciences, Utrecht University, Utrecht, 3584 CB, the Netherlands
  • 12Department of Ocean Sciences, University of California, Santa Cruz, CA, USA
  • 13NORCE Norwegian Research Centre and Bjerknes Centre for Climate Research, 5007 Bergen, Norway
  • 14School of Geography, University of Nottingham, Nottingham, NG7 2RD, UK
  • 15Department of Geosciences, The University of Arizona, Tucson, AZ 85721, USA
  • 16Dept. of Earth and Planetary Sciences, University of California, Santa Cruz, USA

Abstract. 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 concentrations were higher than pre-industrial, but 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, by ~ 2.3 ºC for the combined proxy data (foraminifera Mg/Ca and alkenones), or by ~ 3.2 ºC (alkenones only). Compared to the pre-industrial, 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.

Erin L. McClymont et al.
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Short summary
We examine sea-surface temperature response to an interval of climate ~ 3.2 million years ago, when CO2 concentrations were similar to today and the near-future. Our geological data and climate models show that global mean sea-surface temperatures were 2.3 to 3.2 ºC warmer than pre-industrial climate, that the mid- and high-latitudes warmed more than the tropics, and that the warming was particularly enhanced in the North Atlantic Ocean.
We examine sea-surface temperature response to an interval of climate ~ 3.2 million years ago,...
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