Climate Models: How to Assess Their Reliability

ABSTRACT The paper discusses modelling uncertainties in climate models and how they can be addressed based on physical principles as well as based on how the models perform in light of empirical data. We argue that the reliability of climate models can be judged by three kinds of standards: striking confirmation, supplementing independent causal arguments, and judging the causal core of models by establishing model robustness. We also use model robustness for delimiting confirmational holism. We survey recent results of climate modelling and identify salient results that fulfil each of the three standards. Our conclusion is that climate models can be considered reliable for some qualitative gross features and some long-term tendencies of the climate system as well as for quantitative aspects of some smaller-scale mechanisms. The adequacy of climate models for other purposes is less convincing. Among the latter are probability estimates, in particular, those concerning rare events. On the whole, climate models suffer from important deficits and are difficult to verify, but are still better confirmed and more reliable than parts of the methodological literature suggest.