Assessing Earth's Energy Imbalance Trend in the Early 21st Century in Two High‐Resolution Coupled Models

Abstract Satellite observations since 2001 show an increasing Earth's energy imbalance (EEI) at the top of the atmosphere of 0.45 W m −2 dec −1 , a trend understated in coupled climate models. We assess the 2001–2024 EEI trend in historical simulations of two high‐resolution coupled models, CM4X, a revised version of CM4.0, and CESM‐HR, a high‐resolution version of CESM1, each with 10 realizations. The ensemble‐mean EEI trends in CM4X and CESM‐HR capture only 25% and 55% of the observed trend, respectively, due to underestimated shortwave trends in the tropics and Southern Hemisphere extratropics. CESM‐HR exhibits twice the intramodel variability in EEI and surface warming trends than CM4X, and biases in EEI trends are not linked to warming‐pattern differences. One CESM‐HR realization matches the observed EEI trend but via strong Antarctic offshore polynyas absent from observations. These results highlight the potentially critical influence of sea‐ice processes on near‐term climate projections in high‐resolution models.