Marine Cloud Brightening: from Shipping Emissions to Climate Intervention

Dr Matthew Henry is a Senior Research Fellow at the College of Engineering, Mathematics, and Physical Sciences at the University of Exeter. He is also co-chair of the Geoengineering Model Intercomparison Project. 

"Marine cloud brightening (MCB) has been proposed as a means of temporarily reducing global or regional warming by increasing the reflectivity of low-level marine clouds. After introducing the basic physics underpinning MCB, I will discuss how recent shipping regulations have provided an unprecedented natural experiment by reducing sulphur emissions over the oceans. While recent estimates suggest a radiative forcing of approximately 0.1 W m⁻² from these regulations, our work examines the sensitivity of the UK Earth System Model to subgrid-scale parameterisations of shipping sulphur emissions and evaluates the results against multiple observational constraints. We find that the forcing is more likely to be around 0.3 - 0.4 W m⁻², equivalent to roughly a tenth of the total anthropogenic radiative forcing. Following a brief overview of the engineering challenges associated with deliberately brightening clouds using sea-salt aerosols, I will present recent Earth system modelling work exploring the potential for MCB to offset global warming and mitigate Arctic climate change. I will conclude by discussing the considerable uncertainties surrounding the scalability of MCB and what these imply for interpreting model projections."