Projected Global Diversity of Marine Heatwaves in the 21st Century

Abstract Marine heatwaves (MHWs)—discrete and prolonged warm ocean temperature extremes—can pose serious threats to marine ecosystems. While the previous work of authors has highlighted the diversity of MHWs, future changes in six representative MHW types, under different climate change scenarios, are unknown. Here, we analyze changes in MHW diversity projected for the late 21st century using multi‐model ensembles from CMIP6 under the SSP2‐4.5 and SSP5‐8.5 scenarios. Our results show that under the normal‐emission scenario, annual occurrence days of bimodal MHWs keep increasing, while those of the other five types rise early but level off around 2050. Under the high‐emission scenario, annual occurrence days of three long, intense types keep rising, whereas the other three decline after mid‐century. We further find that higher‐intensity MHWs are increasingly associated with bimodal events. Spatially, MHW distributions shift toward bimodal dominance, with nearly all ocean regions projected to be governed by bimodal types by mid‐century under the both scenarios. Improved understanding of these projected shifts is critical for informing marine conservation planning and climate adaptation strategies in ocean ecosystems.