More equable past and future warm climates in unprecedented high-resolution simulations

Understanding Earth’s past warm climates is crucial for improving climate modeling and future projections. We revisit the early Eocene "Equable Climate Problem", the longstanding mismatch between proxy-inferred weak meridional and seasonal temperature contrasts at ~50 Ma and the overly strong gradients and seasonality simulated by climate models, using the first fully coupled, high-resolution (HR) Eocene simulations. Our simulation employs ~10× finer spatial resolution in both the atmosphere and ocean than conventional low-resolution (LR) models at ~1–2°. The HR simulation produces a more equable Eocene climate, with over 5℃ warmer temperatures in continental interiors during winter and oceanic western boundary current regions. These temperatures more closely align with paleoclimate proxies, reducing the model-proxy discrepancy by ~20–30% relative to LR simulations. The improvements arise from a poleward shifted storm track with stronger wintertime atmospheric storminess at high latitudes, enhancing atmospheric heat transport and downward cloud longwave radiation, along with differences in oceanic eddy heat transport. Parallel HR simulations of future climate change similarly show additional regional and seasonal warming relative to LR. These findings indicate that traditional LR models may systematically underestimate extreme warming in past and future warm climates, underscoring the need for HR simulations in climate research and projections.