Myles Allen, Oxford: Forecast-Based Attribution

COMPASS 2024-09-25: Myles Allen, University of Oxford, UK
"Forecast-Based Attribution: A Probabilistic Approach to Storylines, or a Storyline Approach to Probabilities"

In examining the impact of external climate drivers on extreme weather, there has been a lively discussion of the relative merits of probabilistic versus storyline framings. The probabilistic framing uses large ensembles to assess the impact of an external factor on the occurrence-probability of a certain class of extreme event, inspired in some way by the event that actually occurred. Storylines use detailed simulation of the event itself to assess the role of external factors in its evolution or magnitude. This talk argues that we can use operation seasonal or even medium-range ensemble forecasts to develop a new experimental design for the investigation of causes of extreme weather events that combines some of the advantages of both framings, opening the door to applying the best meteorological simulation tools on the planet to address climate questions. I illustrate the point with one of the most exceptional weather events of recent times, the 2021 heatwave in the Pacific Northwest, and the less exceptional but still damaging Storm Eunice of 2022. Whenever you hear the phrase "impossible without climate change" referring to a short-term weather event, there is probably research to be done.