On the attribution of the impacts of extreme weather events to anthropogenic climate change

S E Perkins-Kirkpatrick,M Wehner,D M Mitchell,A D King,D Frame,J Pastor-Paz,Y T E Lo,S Rosier,D A Stone

doi:10.1088/1748-9326/ac44c8

Abstract

Investigations into the role of anthropogenic climate change in extreme weather events are now starting to extend into analysis of anthropogenic impacts on non-climate (e.g. socio-economic) systems. However, care needs to be taken when making this extension, because methodological choices regarding extreme weather attribution can become crucial when considering the events’ impacts. The fraction of attributable risk (FAR) method, useful in extreme weather attribution research, has a very specific interpretation concerning a class of events, and there is potential to misinterpret results from weather event analyses as being applicable to specific events and their impact outcomes. Using two case studies of meteorological extremes and their impacts, we argue that FAR is not generally appropriate when estimating the magnitude of the anthropogenic signal behind a specific impact. Attribution assessments on impacts should always be carried out in addition to assessment of the associated meteorological event, since it cannot be assumed that the anthropogenic signal behind the weather is equivalent to the signal behind the impact because of lags and nonlinearities in the processes through which the impact system reacts to weather. Whilst there are situations where employing FAR to understand the climate change signal behind a class of impacts is useful (e.g. ‘system breaking’ events), more useful results will generally be produced if attribution questions on specific impacts are reframed to focus on changes in the impact return value and magnitude across large samples of factual and counterfactual climate model and impact simulations. We advocate for constant interdisciplinary collaboration as essential for effective and robust impact attribution assessments.

Highlights

Extreme event attribution (EEA) is a climate science field where the influence of physical drivers is isolated for specific extreme events
A traditional fraction of attributable risk (FAR) analysis yields a range of 0.37–0.5. These results describe the anthropogenic signal behind the frequency of a heat-related mortality impact that causes at least——60 deaths over a single day during June–July in London
A FAR assessment on the corresponding extreme heat has a different signal, between 0.46 and 0.67. This means that 46%–67% of days with London temperatures that exceed 26.6 ◦C are due to anthropogenic climate change (see figure S1 in supplementary material for corresponding return periods)

Summary

Introduction

Extreme event attribution (EEA) is a climate science field where the influence of physical drivers is isolated for specific extreme events. The driver of interest is anthropogenic climate change, considering the influence on the frequency or magnitude of observed extremes. Since its conception (Allen 2003), there has been a wealth of attribution studies assessing how anthropogenic climate change has altered notable and high-impact events (e.g. Peterson et al 2012, Herring et al 2020). There are multiple techniques to undertake event attribution assessments, such as the fraction of attributable risk (FAR) probability framework (Allen 2003, Stott et al 2004, Stone and Allen 2005); the story-line approach (e.g. Hoerling et al 2013, Trenberth et al 2016, Shepherd 2016, Zappa and Shepherd 2017, Patricola and Wehner 2018, Wehner et al 2019, Reed et al 2020); a comparison of model ensembles with different forcings and/or physics While FAR is commonly used in EEA assessments, any method must accurately reflect the attribution question being asked, which should be clear in the initial study design (Otto et al 2012, Stone et al 2021)

Results

Discussion

Conclusion