Current and Future Cloud Brightening from Ships in Marine Low Clouds
It has long been known that emissions of aerosol particles and precursors from large ships can alter the reflectivity of low clouds over the oceans. The influence of aerosol particles on cloud reflectivity is one of the largest sources of uncertainty in our understanding of anthropogenic climate change. Commercial shipping constitutes a large and relatively concentrated aerosol perturbation that can be used to quantify the impacts of aerosols on cloud reflectivity. In this presentation, I will present an analysis of satellite data that show a significant increase in cloud reflectivity associated with enhanced cloud droplet number concentrations within a major shipping corridor in the southeast Atlantic. These results are then used to estimate a global radiative forcing estimate from shipping, which is anticipated to diminish as new fuel-sulfur regulations come into force in 2020. We use the results to make an estimate of the global effective radiative forcing from all anthropogenic sulfate. For the final part of the presentation, I will ask the question of how much more reflective marine clouds could be made if we were to deliberately increase aerosol concentrations over the oceans, a climate intervention proposal known as marine cloud brightening (MCB). This will include a discussion of research being conducted to better quantify the potential efficacy of MCB using field observations and multi-scale modeling.