Substantial Radiative Warming by an Inadvertent Geoengineering Experiment from 2020 Fuel Regulations

Abstract

Human activities affect the Earth’s climate through modifying the composition of the atmosphere, which then creates radiative forcing that drives climate change. The warming effect of anthropogenic greenhouse gases has been partially balanced by the cooling effect of anthropogenic aerosols. In 2020, fuel regulations abruptly reduced the emission of sulfur dioxide from international shipping by more than 80% and created an inadvertent geoengineering experiment with global scale. Here we show the regulation leads to a radiative forcing of 0.12 Wm-² averaged over the global ocean using a combination of modeling and satellite data. The forcing is estimated to effectively double the warming rate of global mean temperature in this decade with strong spatiotemporal heterogeneity. The warming effect contributes 50% to the measured increase in planetary heat uptake since 2020. The radiative forcing also has strong hemispheric contrast of 0.12 Wm-² and contributes to the measured hemispheric contrast in absorbed solar radiation, which has important implications for precipitation patterns. Our result suggests marine cloud brightening may be a viable geoengineering method in temporarily cooling the climate.