Global warming drives a threefold increase in persistence and 1 ◦C rise in intensity of marine heatwaves

Abstract

[eng] Marine heatwaves are extreme climatic events consisting of persistent periods of warmocean waters that have profound impacts on marine life. These episodes are becomingmore intense, longer, and more frequent in response to anthropogenic global warming.Here, we provide a comprehensive and quantitative assessment on the role of globalwarming on marine heatwaves. To do so, we construct a counterfactual version ofobserved global sea surface temperatures since 1940, corresponding to a stationaryclimate without the effect of long-term increasing global temperatures, and use it tocalculate the contribution of global air temperature rise on the intensity and persistenceof marine heatwaves. We determine that global warming is responsible for nearly halfof these extreme events and that, on a global average, it has led to a three-fold increase inthe number of days per year that the oceans experience extreme surface heat conditions.We also show that global warming is responsible for an increase of 1ºC in the maximumintensity of the events. Our findings highlight the detrimental role that human-inducedglobal warming plays on marine heatwaves. This study supports the need for mitigationand adaptation strategies to address these threats to marine ecosystems.