Unlocking Multi-Millennial Eocene Simulations with a New EC-Earth4 Configuration

Modelling rapid climate perturbations in past warm climates of the geological record provides a powerful test for climate models under boundary conditions far outside the historical range. Eocene hyperthermal events are short-lived episodes of rapid greenhouse gas release, and represent the fastest large-scale carbon perturbations in the paleoclimate record. However, the mechanisms governing their onset, magnitude, and recovery remain partially understood due to limitations in proxy data coverage and resolution. Long transient simulations with fully coupled climate models are therefore essential to bridge this gap and to evaluate model behaviour under extreme climate forcing. Here, we present a novel low-resolution paleoclimate configuration (TL63L31–PALEORCA2; ~2.8° atmospheric and ~2° oceanic resolution) of the EC-Earth4 Earth System Model, developed to investigate past warm climate states. This configuration achieves a computational performance of ~230 simulated years per day using 256 MPI cores on the ECMWF ATOS HPC2020 system, enabling computationally efficient multi-century to multi-millennial simulations with a fully coupled atmosphere–ocean climate model. We apply this configuration to the DeepMIP protocol for the Paleocene–Eocene Thermal Maximum (PETM) to investigate Eocene climate dynamics, focusing on (1) atmospheric and oceanic circulation, (2) the hydrological cycle, and (3) regional and global climate extremes.  We assess model proxy mismatches and evaluate the EC-Earth4 integrations in comparison with other DeepMIP integrations. The new configuration also establishes a shared modelling framework that can support paleoclimate research and collaborative model development within the European climate modelling community.