Climate models and robustness analysis – part I:core concepts and premises

Robustness analysis (RA) is the prescription to consider a diverse range of evidence and only regard a hypothesis as well-supported if all the evidence agrees on it. In contexts like climate science, the evidence in support of a hypothesis often comes in the form of model results. This leads to model-based RA (MBRA), whose core notion is that a hypothesis ought to be regarded as well-supported on grounds that a sufficiently diverse set of models agrees on the hypothesis. This chapter, which is the first part of a two-part review of MBRA, begins by providing a detailed statement of the general structure of MBRA. This statement will make visible the various parts of MBRA and will structure our discussion in the remainder of the chapter. We explicate the core concepts of independence and agreement, and we discuss what they mean in the context of climate modelling. Our statement shows that MBRA is based on three premises, which concern robust properties, common structures, and so-called robust theorems. We analyse what these involve and what problems they raise in the context of climate science. In the next chapter, which is the second part of the review, we analyse how the conclusions of MBRA can be justified.