New ACP Letter: Lightning declines over shipping lanes following regulation of fuel sulfur emissions

11 March 2025

Aerosol particles influence clouds, which exert a large forcing on solar radiation and freshwater. To better understand the mechanisms by which aerosol influences thunderstorms, the authors look at the two busiest shipping lanes in the world, where recent regulations have reduced sulfur emissions by nearly an order of magnitude. They find that the reduction in emissions has been accompanied by a dramatic decrease in both lightning and the number of droplets in clouds over the shipping lanes.

Executive editor's statement: Our understanding of the impact of aerosol particles on deep-convective clouds is still incomplete. Earlier research found increased lightning above shipping lanes and hypothesized that the ship emissions support the development of deep-convective cloud systems. The present study investigates the effect of a sevenfold reduction in sulphur content of shipping fuel, implemented following the International Marine Organisation 2020 regulation. A significant decrease in lightning activity is found over shipping lanes in combination with a reduction of both the concentration and the size of the emitted particles, providing further evidence of a strong connection between shipping missions, deep-convective cloud development, and lightning activity. This highlights the need to resolve the still unclear acting mechanisms.

Contact: Joel A. Thornton (joelt@uw.edu)