Materials with smaller absorptivity could reduce detrimental impacts of stratospheric aerosol injection on the hydrological cycle

Abstract Sulfur-based stratospheric aerosol injection (SAI) can reduce greenhouse gas-induced warming, but also reduces global precipitation, and alters the atmospheric circulation through lower stratospheric warming (LSW) from absorption of radiation. We compare the hydrological response to SAI in model simulations using sulfate as geoengineering material versus three alternative materials, alumina, calcite, and diamond dust, which have lower absorptivity but comparable shortwave radiation (SW) scattering. Our results show that the usage of less absorptive materials for SAI reduces perturbations to the atmospheric radiation balance, decreasing global apparent hydrological sensitivity, defined here as total global precipitation change per degree surface cooling. It also limits LSW and circulation changes, with tropical circulation metrics, such as Hadley Cell strength and intertropical convergence zone location being altered less compared to sulfur. It is important to note, however, that simulations involving solid particle injections are subject to substantially larger uncertainties than sulfur-based SAI, particularly related to plume-scale microphysics, stratospheric chemistry, and aerosol-cloud interactions. Despite these uncertainties, our results indicate that, within the present idealized modeling framework, SAI materials with reduced longwave absorptivity have the potential to mitigate key hydrological and dynamical side effects associated with sulfur-based SAI.