In addition to process-level evaluation, CRESCENDO will develop a community benchmarking system for evaluating coupled ESMs. Such a system, named ESMValTool, will benchmark key large-scale aspects of full ESM-simulated variability and trends, comparing to observations, earlier versions of the same ESM or different ESMs, as well as allowing assessment of key measures of Earth system change across a range of projection protocols. ESMValTool v1.0 has been developed in the EU project EMBRACE (http://www.embrace-project.eu; Eyring et al. 2016), where a range of climate performance metrics and diagnostics are developed. In CRESCENDO we will extend this work to include additional biogeochemical and aerosol/trace gas metrics. The aforementioned process-level diagnostics will also be included in the ESMValTool source code repository, making them available to the wider research community. An important goal of ESMValTool is that it becomes a community system, open both to users and developers, encouraging open exchange of evaluation methods in order to avoid duplication of effort.
These two evaluation approaches, bottom-up (process-level) and top-down (full ESM benchmarking), aim to ensure ESMs deliver the correct answer for the correct reasons, while making sure overall realism in full ESM climate states is achieved. Both approaches are necessary to increase confidence in ESMs while retaining scientific rigour.
Eyring, V., Righi, M., Lauer, A., Evaldsson, M., Wenzel, S., Jones, C., et al. (2016). ESMValTool (v1.0) – a community diagnostic and performance metrics tool for routine evaluation of Earth system models in CMIP, Geosci. Model Dev., 9, 1747-1802.