ESMValTool (v1.0) - a community diagnostic and performance metrics tool for routine evaluation of Earth system models in CMIP

This is the final version of the article. Available from European Geosciences Union via the DOI in this record.A community diagnostics and performance metrics tool for the evaluation of Earth system models (ESMs) has been developed that allows for routine comparison of single or multiple models, either against predecessor versions or against observations. The priority of the effort so far has been to target specific scientific themes focusing on selected essential climate variables (ECVs), a range of known systematic biases common to ESMs, such as coupled tropical climate variability, monsoons, Southern Ocean processes, continental dry biases, and soil hydrology-climate interactions, as well as atmospheric CO2 budgets, tropospheric and stratospheric ozone, and tropospheric aerosols. The tool is being developed in such a way that additional analyses can easily be added. A set of standard namelists for each scientific topic reproduces specific sets of diagnostics or performance metrics that have demonstrated their importance in ESM evaluation in the peer-reviewed literature. The Earth System Model Evaluation Tool (ESMValTool) is a community effort open to both users and developers encouraging open exchange of diagnostic source code and evaluation results from the Coupled Model Intercomparison Project (CMIP) ensemble. This will facilitate and improve ESM evaluation beyond the state-of-the-art and aims at supporting such activities within CMIP and at individual modelling centres. Ultimately, we envisage running the ESMValTool alongside the Earth System Grid Federation (ESGF) as part of a more routine evaluation of CMIP model simulations while utilizing observations available in standard formats (obs4MIPs) or provided by the user.The development of the ESMValTool (v1.0) was funded by the European Commission’s 7th Framework Programme, under Grant Agreement number 282672, the “Earth system Model Bias Reduction and assessing Abrupt Climate change (EMBRACE)” project and the DLR “Earth System Model Validation (ESMVal)” and “Klimarelevanz von atmosphärischen Spurengasen, Aerosolen und Wolken: Auf dem Weg zu EarthCARE und MERLIN (KliSAW)” projects. In addition, financial support for the development of ESMValTool (v1.0) was provided by ESA’s Climate Change Initiative Climate Modelling User Group (CMUG). We acknowledge the World Climate Research Program’s (WCRP’s) Working Group on Coupled Modelling (WGCM), which is responsible for CMIP, and we thank the climate modelling groups for producing and making available their model output. For CMIP the US Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. We thank Björn Brötz (DLR, Germany) for his help with the release of the ESMValTool and Clare Enright (UEA, UK) for support with development of the ocean biogeochemistry diagnostics. We are grateful to Patrick Jöckel (DLR, Germany), Ron Stouffer (GFDL, USA) and to the two anonymous referees for their constructive comments on the manuscrip