02 Dec 2022
02 Dec 2022
Status: this preprint is currently under review for the journal CP.

On the climatic influence of CO2 forcing in the Pliocene

Lauren E. Burton1, Alan M. Haywood1, Julia C. Tindall1, Aisling M. Dolan1, Daniel J. Hill1, Ayako Abe-Ouchi2, Wing-Le Chan2, Deepak Chandan3, Ran Feng4, Stephen J. Hunter1, Xiangyu Li5, W. Richard Peltier3, Ning Tan6, Christian Stepanek7, and Zhongshi Zhang8 Lauren E. Burton et al.
  • 1School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, West Yorkshire, LS2 9JT, UK
  • 2Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, 277-8564, Japan
  • 3Department of Physics, University of Toronto, Toronto, M5S 1A7, Canada
  • 4Department of Geosciences, College of Liberal Arts and Sciences, University of Connecticut, Storrs, CT 06033, USA
  • 5Department of Atmospheric Science, School of Environmental Studies, China University of Geoscience, Wuhan, 430074, China
  • 6Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
  • 7Alfred-Wegener-Institut – Helmholtz-Zentrum für Polar and Meeresforschung (AWI), Bremerhaven, 27570, Germany
  • 8NORCE Norwegian Research Centre, Bjerknes Centre for Climate Research, 5007 Bergen, Norway

Abstract. Understanding the dominant climate forcings in the Pliocene is crucial to assessing the usefulness of the Pliocene as an analogue for our warmer future. Here we implement a novel, yet simple linear factorisation method to assess the relative influence of CO2 forcing in seven models of the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) ensemble. Outputs are termed “FCO2” and show the fraction of Pliocene climate change driven by CO2.

The accuracy of the FCO2 method is first assessed through comparison to an energy balance analysis previously used to assess drivers of surface air temperature in the PlioMIP1 ensemble. After this assessment, the FCO2 method is applied to achieve an understanding of the drivers of Pliocene sea surface temperature and precipitation for the first time.

CO2 is found to be the most important forcing in the ensemble for Pliocene surface air temperature (global mean FCO2 = 0.56), sea surface temperature (global mean FCO2 = 0.56) and precipitation (global mean FCO2 = 0.51). The range between individual models is found to be consistent between these three climate variables, and the models generally show good agreement on the sign of the most important forcing.

Our results provide the most spatially complete view of the drivers of Pliocene climate to date, and have implications for both data-model comparison and the use of the Pliocene as an analogue for the future. That CO2 is found to be the most important forcing reinforces that the Pliocene is a good palaeoclimate analogue, but the significant effect of non-CO2 forcing at regional scale reminds us that it is not perfect, and this must not be overlooked. This comparison is further complicated when considering the Pliocene as a state in quasi-equilibrium with CO2 forcing compared to the transient warming being experienced at present.

Lauren E. Burton et al.

Status: open (until 08 Feb 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2022-90', Anonymous Referee #1, 29 Dec 2022 reply
  • RC2: 'Comment on cp-2022-90', Anonymous Referee #2, 04 Feb 2023 reply

Lauren E. Burton et al.

Lauren E. Burton et al.


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Short summary
Warm climates of the Pliocene (~3 million years ago) are similar to projections of the near future. We find elevated concentrations of atmospheric carbon dioxide to be the most important forcing for driving changes in Pliocene surface air temperature, sea surface temperature and precipitation. However, changes caused by the nature of Pliocene ice sheets and orography are also important, affecting the extent to which we can use the Pliocene as an analogue for our warmer future.