Summary report on the evaluation of post-CMIP6 ESMs, with recommendations for priority areas for future model development

This deliverable 4.1 presents an evaluation of the representation of mean states, variability, and key process interactions in the set of post-CMIP6 Earth System Models (ESMs) considered in OptimESM. Building on tools and diagnostics developed during the initial project phase, the analysis is applied to the historical simulations accomplished with the four post-CMIP6 ESMs, also considering the CMIP6 model ensemble for reference. The evaluation covers five major components of the Earth system: the physical ocean, biogeochemical ocean, atmosphere, cryosphere, and land-vegetation systems. In addition to the assessment of large-scale mean and variability, the analysis focuses on the capacity of the models to capture abrupt changes and the underlying processes and feedbacks. Observational datasets — both newly identified and previously established — serve as benchmarks for evaluating model performance. The results provide critical insights into current model capabilities and limitations, and serve as the basis for recommendations on future ESM developments.