Efficacy assessment of stratospheric aerosol scrubbing as a counter climate intervention strategy

Stratospheric Aerosol Injection (SAI) has been proposed to counteract global warming. Countering SAI may prove attractive to actors who oppose deployment and methods have been suggested but not tested for efficacy. Using a global climate model with double moment aerosol microphysics, we perform an initial assessment of ‘Stratospheric Aerosol Scrubbing’ (SAS) scenarios where coarse aerosol is deliberately injected to enhance aerosol growth, reduce particle radiative efficiency, and enhance sedimentation thereby reducing SAI impacts. We simulate two idealised equatorial SAI and SAS scenarios: pulse interventions lasting 2 months, and sustained interventions lasting 20 years. We find that SAS reduces the global Stratospheric Aerosol Optical Depth by 30-40 % when the calcite mass is equal to the sulphur dioxide (SO2) mass in the pulse intervention and half of the SO2 mass in the sustained intervention. The global radiative impact in the sustained simulations is reduced from -3.3 Wm-2 to -2.3 Wm-2 under SAS, a counterbalancing of approximately 30 %. Our results suggest that SAS could be effective at offsetting SAI impacts and warrants further research.