Nonlinear climate response to regional brightening of tropical marine stratocumulus

To counteract global warming, there have been suggestions to increase the albedo of low-level marine clouds through the aerosol indirect effects by injecting them with sea salt. However, the full climate response to this geoengineering scheme is currently poorly understood. We simulate cloud seeding in a coupled mixed-layer ocean-atmosphere general circulation model in order to identify the specific physical mechanisms through which seeding could perturb the climate system's radiative balance, and cause temperature and precipitation changes. Seeding stratocumulus decks over three tropical maritime regions in the North Pacific, South Pacific and South Atlantic produces strong local reductions in solar absorption. Over half of the radiative cooling is due to direct scattering of solar radiation by the added sea salt aerosols, while the rest comes from enhancement of the local cloud albedo. The oceanic cooling due to the seeding over the southeastern equatorial Pacific induces a La Niña-like response, with tropical precipitation changes resembling La Niña anomalies and teleconnections occurring in the mid-latitude North Pacific and North America. Additionally, model runs in which only one of the three regions is seeded indicate nonlinearity in the climate response. We identify dynamical and thermodynamical constraints respectively on the temperature and hydrological cycle responses to cloud seeding, but the full response to such geoengineering remains poorly constrained.