Climate Intervention through Stratospheric Aerosol Injection may partially mitigate marine heatwaves

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Marine heatwaves (MHWs) cause significant harm to marine life and ecosystem services, and can intensify hurricanes. Global warming has increased the duration and intensity of MHWs over the last century, and permanent MHWs have been predicted in many areas of the ocean by the end of the 21st century. Climate interventions, such as stratospheric aerosol injection (SAI), have been proposed to reduce the mean global temperature; however, their potential impact on MHWs is unclear. In this study, we used the output from the Community Earth System Model to quantify MHWs under multiple timeframes and climate change scenarios. We evaluated MHW properties, including duration and maximum intensity, over the historical (1990-2009), present (2015-2034), and future (2050-2069) periods. We analyzed output from two SAI scenarios aimed to maintain global mean surface temperatures at ∼1.5 and ∼1.0°C above pre-industrial levels (ARISE-SAI-1.0 and ARISE-SAI-1.5) and one non-SAI scenario (SSP2-4.5). Our results show that despite the SAI reducing the global average maximum intensity and duration of MHWs relative to SSP2-4.5, the magnitude of the effects varies spatially. Compared with the present climate, SAI scenarios would reduce MHW intensity in 25-76% of the ocean and MHW duration in 21-80% of the ocean. The largest future reductions in maximum intensity and duration occurred in the coastal regions of the Tropical Atlantic, Indian, Arctic, and South Atlantic oceans. Even with a more aggressive SAI scenario (ARISE-SAI-1.0), nearly 25% of the ocean would remain unaffected, with areas like the North Atlantic, Tropical Pacific, and parts of the Southern Oceans still experiencing more intense and longer MHWs, posing risks to marine life.

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