Aerosol-cloud interactions make a large but also very uncertain contribution to present-day global climate forcing; they are leveraged locally to induce or suppress precipitation (“cloud seeding”); and they are being considered as a possible mechanism for slowing climate warming through two climate intervention approaches (brightening low-lying marine clouds or thinning high-altitude cirrus clouds). While these categories of aerosol-cloud interactions have differences in being unintentional (the first) or intentional (the latter two), and with very different end-goals, all three share common physics and sources of uncertainty. Further, while cloud seeding is a technology historically used to enhance precipitation over local watersheds, some regions are now deploying larger-scale cloud seeding efforts to have more regional impacts on water resources, bringing the scale at which it would operate closer to that from inadvertent aerosol-cloud interactions or for climate intervention. All three have in common the need to better understand cloud responses to aerosol perturbations across a range of scales, how these responses depend on the background aerosol and meteorological conditions, and on feedbacks from the cloud responses back to the aerosol itself.

This session invites presentations on these processes, spanning climate forcing, regional precipitation enhancement, and regional-to-global climate intervention, using numerical modeling studies, analyses of observations of deliberate cloud seeding (e.g., SNOWIE), and studies of inadvertent analogues (e.g., ship tracks and contrails). This session aims to bring together scientists from both the weather and climate fields to foster dialogue in an area of common interest.