Quantifying the impact of anthropogenic warming on observed marine heatwaves

Marine heatwaves (MHWs) are periods of persistently elevated sea temperatures that pose significant threats to marine ecosystems and coastal economies. In this study, we provide a quantitative assessment of the influence of anthropogenic global warming on the intensity and persistence of MHWs using a novel counterfactual climate framework. This approach removes the effects of long-term global air temperature increases from observed sea surface temperature records while preserving natural variability.

Our analysis reveals that anthropogenic global warming has caused a threefold increase in the duration of MHW conditions globally, with oceans experiencing an average of 34 additional days per year under extreme heat conditions since 1940. Furthermore, the maximum intensity of these events has increased by 1°C on average, with regional hotspots such as the Mediterranean Sea experiencing amplified impacts. These findings highlight the dominant role of human-induced warming in driving observed changes in MHW characteristics and underscore the need for targeted mitigation and adaptation strategies.