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Abstract 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 carbon emissions by the 2050s, called carbon neutrality, were proposed. Here, we evaluate the impact of carbon neutrality on MHWs in the late 21st 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 continues (i.e., SSP3‐7.0), the MHWs in the late 21st century will become stronger and longer 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 MHWs can be significantly reduced by achieving carbon neutrality (i.e., SSP1‐1.9). In particular, the spatial proportion of the ocean exposed to permanent MHWs can be reduced to as low as 0.02%–0.07%, depending on the regions. This result underscores the critical importance of ongoing efforts to achieve net‐zero carbon emissions to reduce the potential ecological risks induced by extreme MHWs.

Abstract Climate extremes, such as hot temperature and heavy precipitation events, have devastating effects on human societies. As the planet gets warmer, they have become more intense and more frequent. To avoid irreversible damages from climate extremes, many countries have committed to achieving net‐zero anthropogenic carbon emissions, or carbon neutrality, by the 2050s. Here, we quantify the impact of carbon neutrality on population exposure to climate extremes 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 the increasing population exposure to hot‐temperature and heavy‐precipitation extremes under SSP3‐7.0 scenario can be substantially reduced by 87%–98% in the late 21st century by achieving the carbon neutrality based on SSP1‐1.9 scenario. The benefits of carbon neutrality are particularly pronounced in Africa and Asia. The potential benefits of carbon neutrality are also significant in North America, Europe, and Oceania, where a reduction in climate extremes is more than twice as important as population decline in reducing population exposure to climate extremes. These results provide important scientific support for ongoing efforts to achieve net‐zero carbon emissions by the 2050s to reduce potential climate risk and its inequity across continents.

Abstract Population aging, an increasing share of the elderly to the total population, can exacerbate heat vulnerability to intensified heat hazards. However, the aging impacts on increases in exposure of the elderly to unprecedented hot summers (UHSs) could be variable in the warming climate. Here, we present considerable contribution of age structure changes to increases in the elders' exposure to intensified UHSs in countries with a high percentage of youth population, namely, China, India, and Brazil, by analyzing combined scenarios of climate change with population structure. In the aforementioned regions, increases in exposure to stronger UHSs relevant to rapid aging will exceed at least half of the warming impact, which primarily causes frequent occurrence of stronger UHSs. Conversely, the United States and Europe, which have already entered an aged society, show a negligible aging impact. These results suggest that the future evolution of a society's age structure is an important constraint for projecting population exposure to strengthened summer heat.