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Challenges in quantifying Pliocene terrestrial warming revealed by data–model discord


Comparing simulations of key warm periods in Earth history with contemporaneous geological proxy data is a useful approach for evaluating the ability of climate models to simulate warm, high-CO2 climates that are unprecedented in the more recent past1,2,3. Here we use a global data set of confidence-assessed, proxy-based temperature estimates and biome reconstructions to assess the ability of eight models to simulate warm terrestrial climates of the Pliocene epoch. The Late Pliocene, 3.6–2.6 million years ago, is an accessible geological interval to understand climate processes of a warmer world4. We show that model-predicted surface air temperatures reveal a substantial cold bias in the Northern Hemisphere. Particularly strong data–model mismatches in mean annual temperatures (up to 18 °C) exist in northern Russia. Our model sensitivity tests identify insufficient temporal constraints hampering the accurate configuration of model boundary conditions as an important factor impacting on data–model discrepancies. We conclude that to allow a more robust evaluation of the ability of present climate models to predict warm climates, future Pliocene data–model comparison studies should focus on orbitally defined time slices5.

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Figure 1: Zonally averaged mean annual SAT in degrees Celsius.
Figure 2: Location of 208 palaeobotanical sites used for DMC.
Figure 3: DMC of SATs.

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Financial support was provided by grants to U.S. and A.M.H. from the Natural Environment Research Council, NERC (NE/I016287/1). A.M.D. and A.M.H. acknowledge financial support from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 278636. D.J.L. and F.J.B. acknowledge the NERC grant NE/H006273/1. U.S., A.M.D., H.J.D. and A.M.H. thank the US Geological Survey John Wesley Powell Center for Analysis and Synthesis. W-L.C. and A.A-O. acknowledge financial support from the Japan Society for the Promotion of Science and computing resources at the Earth Simulator Center, JAMSTEC. H.J.D. acknowledges the continued support of the US Geological Survey Climate and Land Use Change Research and Development Program; D.J.H. acknowledges the Leverhulme Trust for the award of an Early Career Fellowship and the National Centre for Atmospheric Research and the British Geological Survey for financial support. G.L. received financial support through the Helmholtz research programme PACES and the Helmholtz Climate Initiative REKLIM. C.S. acknowledges financial support from the Helmholtz Graduate School for Polar and Marine Research and from REKLIM. B.O-B. and N.A.R. recognize the National Center for Atmospheric Research is sponsored by the US National Science Foundation and computing resources were provided by the Climate Simulation Laboratory at the National Center for Atmospheric Research’s Computational and Information Systems Laboratory sponsored by the National Science Foundation and other agencies.

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U.S. synthesized the palaeobotanical proxy data and designed and completed the confidence assessments. U.S., M.J.P., J.V. and H.J.D. carried out the DMC. A.M.D. and A.M.H. carried out the comparisons of model performance and the BIOME4 simulations. W-L.C. performed the additional sensitivity experiments using MIROC. D.J.H. carried out the energy balance analysis. All other authors performed general circulation model simulations that contributed to the PlioMIP Project and discussed the results and commented on the manuscript.

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Correspondence to Ulrich Salzmann.

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The authors declare no competing financial interests.

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Salzmann, U., Dolan, A., Haywood, A. et al. Challenges in quantifying Pliocene terrestrial warming revealed by data–model discord. Nature Clim Change 3, 969–974 (2013).

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