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==== 1.5.4.5 Model Evaluation Tools ====

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For the first time in CMIP, a range of comprehensive evaluation tools are now available that can run alongside the commonly used distributed data platform – Earth System Grid Federation (ESGF; see Annex II) – to produce comprehensive results as soon as the model output is published to the CMIP archive.

For instance, the Earth System Model Evaluation Tool (ESMValTool; [[#Eyring--2020|Eyring et al., 2020]] ; [[#Lauer--2020|Lauer et al., 2020]] ; [[#Righi--2020|Righi et al., 2020]] ) is used by a number of chapters. It is an open-source community software tool that includes a large variety of diagnostics and performance metrics relevant for coupled Earth system processes, such as for the mean, variability and trends, and it can also examine emergent constraints ( [[#1.5.4.7|Section 1.5.4.7]] ). ESMValTool also includes routines provided by the WMO Expert Team on Climate Change Detection and Indices for the evaluation of extreme events ( [[#Min--2011|Min et al., 2011]] ; [[#Sillmann--2013|Sillmann et al., 2013]] ) and diagnostics for key processes and variability. Another example of an evaluation tool is the CLIVAR 2020 ENSO metrics package ( [[#Planton--2021|Planton et al., 2021]] ).

These tools are used in several chapters of this report for the creation of the figures that show CMIP results. Together with the Interactive Atlas, they allow for traceability of key results, and an additional level of quality control on whether published figures can be reproduced. It also provides the capability to update published figures with, as much as possible, the same set of models in all figures, and to assess model improvements across different phases of CMIP ( [[IPCC:Wg1:Chapter:Chapter-3#3.8.2|Section 3.8.2]] ).

These new developments are facilitated by the definition of common formats for CMIP model output ( [[#Balaji--2018|Balaji et al., 2018]] ) and the availability of reanalyses and observations in the same format as CMIP output (obs4MIPs; [[#Ferraro--2015|Ferraro et al., 2015]] ). The tools are also used to support routine evaluation at individual model centres and simplify the assessment of improvements in individual models or generations of model ensembles ( [[#Eyring--2019|Eyring et al., 2019]] ). Note, however, that while tools such as ESMValTool can produce an estimate of overall model performance, dedicated model evaluation still needs to be performed when analysing projections for a particular purpose, such as assessing changing hazards in a given region. Such evaluation is discussed in the next section, and in greater detail in later chapters of this Report.

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