Behind the veil of extreme event attribution

Since Allen (Nature 421(6926):891–892, 2003)’s seminal article, the community of extreme event attribution (EEA) has grown to maturity. Several approaches have been developed: the main ones are the “risk-based approach” — estimating how the probability of event occurrence correlates with climate change — and the “storyline approach” — evaluating the influence of climate change on thermodynamic processes leading to the event. In this article, we map the ways to frame attribution used in a collection of 105 case studies from five BAMS (Bulletin of American Meteorological Society) special issues on extreme events. In order to do so, we propose to define EEA, based on two corpora of interviews conducted with researchers working in the field, as follows: EEA is the ensemble of scientific ways to interpret the question “was this event influenced by climate change?” and answer it. In order to break down the subtleties of EEA, we decompose this initial question into three main problems a researcher has to deal with when framing an EEA case study. First, one needs to define the event of interest. Then, one has to propose a way to link the extreme event with climate change, and the subsequent level of conditioning to parameters of interest. Finally, one has to determine how to represent climate change. We provide a complete classification of BAMS case studies according to those three problems.