It is important to understand connections between society and the natural environment for anticipating environmental hazards and anthropogenic effects on the broader Earth system. In this study, we conduct a detailed exploration of the interactions between oceanic thunderstorms and maritime traffic. Shipping traffic produces aerosols that perturb the otherwise “clean” ocean environment. Prior work proposed these aerosol effects as the cause of increased lightning activity over certain shipping lanes. However, introducing tall well-grounded objects into a high electric field environment might also facilitate lightning discharges, as we see with upward lightning over land. We consider both possibilities in this work.

Our analyses of the thunderstorms responsible for the enhanced lightning activity over the shipping lane with the clearest anthropogenic signal indicate that the anthropogenic signature results from an increased frequency of lightning-producing storms. We did not find evidence of variations in the microphysical parameters describing the storms over shipping lanes and other nearby oceanic regions that might suggest aerosol effects. In contrast, matching lightning stroke data with ship transponder events in oceanic regions where public data are available reveals a strong signal from direct ship interactions with lightning that results in a 1-2 orders of magnitude increase in stroke frequency at current ship locations compared to other nearby regions. These results highlight the central role of direct ship interactions in explaining lightning enhancements over shipping lanes.

We also document the frequency of these direct lightning interactions across various categories of vessels and on individual ships present in the public data.