Multi-model ensembles in climate science: mathematical structures and expert judgements

Julie Jebeile (1) , Michel Crucifix (2)

1 UNIBE - Universität Bern / University of Bern
2 FNRS - Fonds National de la Recherche Scientifique [Bruxelles]

Projections of future climate change cannot rely on a single model. It has become common to rely on multiple simulations generated by Multi-Model Ensembles (MMEs), especially to quantify the uncertainty about what would constitute an adequate model structure. But, as Parker points out (2018), one of the remaining philosophically interesting questions is: “How can ensemble studies be designed so that they probe uncertainty in desired ways?” This paper offers two interpretations of what General Circulation Models (GCMs) are and how MMEs made of GCMs should be designed. In the first interpretation, models are combinations of modules and parameterisations; an MME is obtained by “plugging and playing” with interchangeable modules and parameterisations. In the second interpretation, models are aggregations of expert judgements that result from a history of epistemic decisions made by scientists about the choice of representations; an MME is a sampling of expert judgements from modelling teams. We argue that, while the two interpretations involve distinct domains from philosophy of science and social epistemology, they both could be used in a complementary manner in order to explore ways of designing better MMEs.

Mots clés: Parameterisation; Expert judgement; Climate model; Multi-model ensemble; Climate uncertainty; Mathematical representation

Domaines: Histoire, Philosophie et Sociologie des sciences

Julie Jebeile, Michel Crucifix. Multi-model ensembles in climate science: mathematical structures and expert judgements. Studies in History and Philosophy of Science Part A, In press, ⟨10.1016/j.shpsa.2020.03.001⟩. ⟨hal-02541285⟩