Significant reduction of potential exposure to extreme marine heatwaves by achieving carbon neutrality

Marine heatwave (MHW), a prolonged period of anomalously warm seawater, has a catastrophic repercussion on marine ecosystems. With global warming, MHWs have become increasingly frequent, intense, and prolonged. To avoid irreversible damages from such extreme events, net-zero human-caused carbon emissions by 2050s, called carbon neutrality, were proposed. Here, we evaluate the impact of carbon neutrality on MHWs in the late 21^st century using multi-model projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) Shared Socioeconomic Pathway (SSP)1-1.9 and SSP3-7.0 scenarios. It is found that if the current “regional rivalry” over carbon emissions policy continues into this century (i.e., SSP3-7.0), the MHWs in the late 21^st century will become stronger over 1°C and longer lasting over 365 days than historical ones, especially in the western boundary current and equatorial current regions. Approximately 68% of the global ocean will be exposed to permanent MHWs, regionally 93% in the Indian Ocean, 76% in the Pacific Ocean, 68% in the Atlantic Ocean, 65% in the Coastal Ocean, and 48% in the Southern Ocean. Such extreme MHWs can be significantly reduced by achieving carbon neutrality (i.e., SSP1-1.9). In particular, the proportion of exposure to permanent MHWs can be reduced to as low as 0.02 to 0.07%, depending on the region. This result underscores the critical importance of ongoing efforts to achieve net-zero carbon emissions to reduce the potential ecological risks induced by extreme MHW exposure.