21 Apr 2021

21 Apr 2021

Review status: this preprint is currently under review for the journal CP.

Simulation of the mid-Pliocene Warm Period using HadGEM3: Experimental design and results from model-model and model-data comparison

Charles J. R. Williams1,6, Alistair A. Sellar2, Xin Ren1, Alan M. Haywood3, Peter Hopcroft4, Stephen J. Hunter3, William H. G. Roberts5, Robin S. Smith6, Emma J. Stone1, Julia C. Tindall3, and Daniel J. Lunt1 Charles J. R. Williams et al.
  • 1School of Geographical Sciences, University of Bristol, UK
  • 2Met Office Hadley Centre, UK
  • 3School of Earth and Environment, University of Leeds, UK
  • 4School of Geography, Earth and Environmental Sciences, University of Birmingham, UK
  • 5Department of Geography and Environmental Sciences, Northumbria University, UK
  • 6NCAS, Department of Meteorology, University of Reading, UK

Abstract. Here we present the experimental design and results from a new mid-Pliocene simulation using the latest version of the UK’s physical climate model, HadGEM3-GC31-LL, conducted under the auspices of CMIP6/PMIP4/PlioMIP2. Although two other paleoclimate simulations have been recently run using this model, they both focused on more recent periods within the Quaternary and therefore this is the first time this version of the UK model has been run this far back in time. The mid-Pliocene Warm Period, ~3 Ma, is of particular interest because it represents a time period when the Earth was in equilibrium with CO2 concentrations roughly equivalent to those of today, providing a possible analogue for current and future climate change.

The implementation of the Pliocene boundary conditions is firstly described in detail, based on the PRISM4 dataset, including CO2, ozone, orography, ice mask, lakes, vegetation fractions and vegetation functional types. These were incrementally added into the model, to change from a preindustrial setup to Pliocene conditions.

The results of the simulation are then presented, which are firstly compared with the model’s pre-industrial simulation, secondly with previous versions of the same model and with available proxy data, and thirdly with all other models included in PlioMIP2. Firstly, the comparison with preindustrial suggests that the Pliocene simulation is consistent with current understanding and existing work, showing warmer and wetter conditions, and with the greatest warming occurring over high latitude and polar regions. The global mean surface air temperature anomaly at the end of the Pliocene simulation is 5.1 °C, which is the 2nd highest of all models included in PlioMIP2 and is consistent with the fact that HadGEM3-GC31-LL has one of the highest Effective Climate Sensitivities of all CMIP6 models. Secondly, the comparison with previous generation models and with proxy data suggests a clear increase in global sea surface temperatures as the model has undergone development. Up to a certain level of warming, this results in a better agreement with available proxy data, and the “sweet spot” appears to be the previous CMIP5 generation of the model, HadGEM2-AO. The most recent simulation presented here, however, appears to show poorer agreement with the proxy data compared with HadGEM2, and may be overly sensitive to the Pliocene boundary conditions resulting in a climate that is too warm. Thirdly, the comparison with other models from PlioMIP2 further supports this conclusion, with HadGEM3-GC31-LL being one of the warmest and wettest models in all of PlioMIP2 and, if all the models are ordered according to agreement with proxy data, HadGEM3-GC31-LL ranks approximately halfway among them.  

Charles J. R. Williams et al.

Status: open (until 16 Jun 2021)

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Charles J. R. Williams et al.

Charles J. R. Williams et al.


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Short summary
Computer simulations of the geological past are an important tool to improve our understanding of climate change. We present results from a simulation using the latest version of the UK’s climate model, the mid-Pliocene (approximately 3 million years ago). The simulation reproduces temperatures as expected, and shows some improvement relative to previous versions of the same model. The simulation is, however, arguably too warm when compared to other models and available observations.