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Super Warm Early Eocene Simulations With HadGEM3‐GC31‐LL

Year: 2026
Type: article
Abstract: The early Eocene Climatic Optimum (EECO; 53.3–49.1 million years ago) represents the period of greatest sustained warmth in the Cenozoic (last 66 million years), with proxy‐data indicating global‐mean temperatures 10–16°C above preindustrial and atmospheric concentrations of 1,200–2,500 ppmv. This extreme greenhouse climate provides insights into Earth's climate sensitivity and feedback mechanisms and offers a stress‐test for evaluating climate models under vastly different boundary conditions. Here we present the first application of the HadGEM3‐GC31‐LL model to the super‐warm EECO. We implement methodological improvements to enable stable and efficient simulations, including an updated ozone‐redistribution scheme which ensures that ozone does not enter the troposphere, and a new method for initializing ocean temperatures which reduces the equilibrium time. We perform four millennial‐scale simulations at concentrations between 1 and 4 preindustrial levels (280–1,120 ppmv), using standardised DeepMIP‐Eocene paleogeography and vegetation. Simulated global‐mean surface temperatures reach up to 31.8°C, exceeding available reconstructions despite concentrations at the lower end of proxy estimates, consistent with the model's high equilibrium climate sensitivity of 5.4°C. However, HadGEM3 produces among the lowest meridional temperature gradients (MTGs) in the DeepMIP ensemble and within proxy‐derived ranges, with MTGs decreasing linearly with warming by up to 26% relative to preindustrial. Precipitation shows strong ‐sensitivity and comparatively small biases across latitudes, supporting a link between more realistic MTG simulation and reduced dry‐biases in extratropical precipitation. These results highlight the potential and limitations of applying a high‐ECS model to extreme paleoclimates, both for better understanding past climates and for benchmarking model performance.
DOI: 10.1029/2025jd046219
Authors: Sebastian Steinig, Charles J. R. Williams, Natalie J. Burls, Marlow J. Cramwinckel, Alex Farnsworth, Gavin L. Foster, Peter O. Hopcroft, Gordon N. Inglis, Caroline H. Lear, Annette Osprey, Richard D. Pancost, Zikun Ren, William H. G. Roberts, Alistair A. Sellar, Emma L. Stone, Richard Wood, Jiang Zhu, Daniel J. Lunt
Institutions: University of Bristol, University College London, George Mason University, Utrecht University, University of Southampton, University of Birmingham, Cardiff University, University of Reading, Northumbria University, Met Office, NSF National Center for Atmospheric Research
Language: English
Open Access status: hybrid
Estimated APC paid: $4,070
Funders: National Science Foundation, National Center for Atmospheric Research, Royal Society, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, HORIZON EUROPE Framework Programme, Natural Environment Research Council
Awards: SWEET:Super-Warm Early Eocene Temperatures and climate: understanding the response of the Earth to high CO2 through integrated modelling and data, The Management and Operation of the National Center for Atmoshperic Research (NCAR), G3640513476, G3667093952, G6287184903, SWEET:Super-Warm Early Eocene Temperatures and climate: understanding the response of the Earth to high CO2 through integrated modelling and data, G7084474688, G89739986, G9001175500
OpenAlex ID: W7214183448
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