Human activities impact Earth's climate by altering atmospheric composition, creating radiative forcing that drives climate change. The warming effect of greenhouse gases is partially offset by the cooling effect of anthropogenic aerosols. In 2020, fuel regulations drastically reduced sulfur dioxide emissions from international shipping (by ~80%), creating an unintended geoengineering termination shock. This study estimates a resulting radiative forcing of +0.2 ± 0.11 Wm⁻², potentially doubling the warming rate of the 2020s compared to previous decades. This warming aligns with recent observations and is equivalent to 80% of the measured increase in planetary heat uptake since 2020. The forcing shows strong hemispheric contrast, impacting precipitation patterns. The findings suggest marine cloud brightening as a potential, albeit challenging, geoengineering method.
