 What is known about the ingredients of a climate model—e.g., that they closely approximate accepted theory or involve massive simplifications—can provide reasons to think that the model is similar (or not) to the climate system in particular ways or adequate (or not) for particular purposes (Baumberger et al. 2017). But climate scientists also seek evidence regarding similarity and adequacy by comparing model results to observations (see also Guillemot 2010). Such comparisons can be qualitative or quantitative, as noted above. In some cases, it is relatively straightforward to gauge whether model-data comparisons provide evidence for or against hypotheses about model-system similarities or about the adequacy of climate models for particular purposes. Prime candidates include cases in which what is hypothesized entails just a rough fit between model results and well-observed climate system behaviors. Thus, for example, the Intergovernmental Panel on Climate Change (IPCC) is able to report 