Attributing Historical Increases in Tropical Cyclone Intensities to Human-Driven Sea Surface Temperature Warming

Major tropical cyclones are becoming increasingly common in our warming world, threatening coastlines worldwide and accounting for fifteen billion-dollar disasters in the United States since 2020 alone. Determining the extent to which human-driven climate change bolstered these storms’ observed intensities is challenging—due to data limitations, modeling constraints, and uncertainties in physical processes—but remains an important goal. Social science research suggests that prompt and reliable communication attributing weather extremes will increase people’s perception of climate change’s role in influencing extreme weather events. This helps the public connect the dots between carbon dioxide emissions and local impacts, potentially motivating adaptation and mitigation.

In this study we develop and use an attribution system to investigate how attributable sea surface temperature (SST) warming has influenced historical increases in observed tropical cyclone intensities. Building on recent advances in climate attribution science, the system uses multi-method and statistical approaches pioneered by World Weather Attribution (WWA) and adapted to the daily scale (Gilford et al. 2022).

Using observations and CMIP6 simulations, the attribution system estimates how historical SST distributions have evolved in response to global warming compared with a counterfactual (i.e. a hypothetical world without human greenhouse gas emissions). The approach synthesizes attribution estimates across multiple lines of evidence, and considers confounding aerosol influences in the North Atlantic. The resulting attributable SST changes are used to drive historical and counterfactual potential intensity calculations, which idealize tropical cyclones as heat engines fueled by warm ocean temperatures. Finally, we use a robust statistical relationship between historical observed intensities and potential intensities to specifically quantify how human-warmed SSTs may have intensified recent major tropical cyclones in the North Atlantic and West Pacific basins.

Results show that attributable SST warming has made major tropical cyclones more likely in the last decade than during any previous period on record. While attributing the likelihoods of individual tropical cyclone intensities remains to a degree uncertain, preliminary estimates exhibit attributable influences on particular storms from human-warmed SSTs. We highlight that these findings are subtle and specific, and great care should be taken to effectively compute and communicate hurricane intensity attribution. We conclude by considering the system’s limitations, and discussing exciting future opportunities to advance tropical cyclone attribution science and communication.