Research Seminar Spring 2021

The importance of modeling for climate projection and understanding of past and present climate is clear and has been widely evaluated by the philosophy community. However, an equally important feature has received little attention, the uses of expert judgment within climate science. In this paper, based on a systematic examination of the instances of expert judgment in climate science, we identify and characterize three contexts of use. We then outline the primary epistemological foundations of expert judgment in climate science drawing from both social epistemology and philosophy of science.

An alternative possibilistic perspective has been suggested in order to avoid the deficiencies of the probabilistic approach in climate modelling. This possibilistic perspective raises the epistemological question of the justification of serious possibilities in the climate context. This paper aims to show how recent work in climate science (and in particular in the field of extreme event attribution) can help to address this ‘possibilistic challenge’. We investigate to what extent the sort of qualitative (and causal) understanding at play within the storyline approach (relying on thermodynamical considerations) can help to ground serious possibilities in the context of climate change.

The dialogue between the expert and the policy-maker follows a slippery path. A same word can evoke very different realities or actions in the minds of one or the other. In this respect, the subject of climate is perhaps particularly perilous because the scientific and societal context is conducive to the emergence of new expressions: climate breakdown, tipping points or hothouse Earth. Even though these expressions happen to be used by the experts themselves, they are too young to be considered as reflecting well established, stable technical concepts with broad scientific consensus. Rather, they are value-loaded metaphors that the experts use to express the dangerousness of ongoing climate change, and thus awaken our sense of responsibility towards future generations. Morally, the approach is justified and is in line with the ethics endorsed by the philosopher Hans Jonas, who appealed to the heuristics of fear.

However, perhaps in part because they are not well formalised, these expressions can feed into representations that are rather removed from the experts' judgement. For example, the experts do not believe that there is a threshold of global warming that could be crossed in the foreseeable future, which would be "runaway" and make any form of intervention ineffective. Yet, this idea can be sustained by metaphors such as "hothouse earth" or "tipping point". Thus, the heuristics of fear may contravene another principle, according to which political action can only be responsible if it is accurately informed of the consequences of policy decisions.

This talk by a climate scientist in front of an audience of philosophers ambitions to clarify these metaphors in an open dialog in order to address the dilemmas generated by climate change expertise. To this end, we will dwell on the physical and mathematical rationale of "tipping points" and "anthropocene trajectories", and suggest a critique of their usage in the technical context.

Although climate scientists prefer to express their knowledge about climate change in a ’single, definitive’ manner (i.e. statement with a confidence level), I will argue that information about climate change is often more usefully represented in a ‘plural, conditional’ manner. This is particularly the case at the local scale, where a trade-off between reliability and informativeness is inevitable when one has to decide on the level of aggregation that is appropriate. This has implications for the design and use of model ensembles and their synthesis with the observed record.