Observational evidence of reduced Bay of Bengal lightning since 2020 linked to cloud responses to shipping emission regulations

Lightning plays a crucial role in the Earth’s biogeochemical cycle. Frequent lightning activity over the Bay of Bengal (BoB) has been attributed to shipping emissions through aerosol–cloud interactions in modeling studies but lacks observational confirmation. Here, we present observational evidence linking frequent lightning to the response of deep clouds to ship-emitted sulfate aerosols. These aerosols cause higher cloud tops in mid-to-high clouds, smaller cloud droplet sizes at the bases of low clouds, and increased ice water content with smaller ice particles in deep clouds along shipping lanes, resulting in more lightning strikes than in surrounding areas. The 2020 fuel regulation, which reduced SO₂ emissions by 66% over the BoB, led to lower cloud tops, reduced ice water content, larger cloud droplets, and consequently an 11% decline in lightning frequency during the period of 2020–2023 relative to its climatology. Our findings indicate that shipping emissions contribute at least 17% to the lightning frequency in the BoB region. This study provides observational evidence that changes in shipping emissions—particularly those driven by recent regulations—can significantly influence lightning frequency by altering the microphysical properties of deep clouds. It underscores the broader atmospheric impact of maritime policies, extending beyond local radiative effects to influence convective processes and natural hazards.