Chemical and climatic impacts of stratospheric aerosol injections: can aerosols with smaller infrared absorptivity reduce undesired side-effects?

Stratospheric aerosol injection (SAI) is one of the most researched Solar Radiation Modification strategies to counteract greenhouse-gas-induced warming. However, conventional approaches involve the injection of gaseous SO2 (S-based SAI). Due to the substantial lower-stratospheric heating they lead, S-based SAI alter precipitation and circulation patterns and potentially also ocean circulation. Our work explores the risks and benefits of alternative materials—alumina, calcite, and diamond dust—with markedly lower infrared absorptivity but similar shortwave scattering properties to sulfate. We consistently show that these less absorptive particles reduce lower-stratospheric warming, resulting in reduced hydrological and dynamical responses. These materials can potentially reduce disruptions in key circulation metrics such as Hadley Cell strength, ITCZ position, the North Atlantic Oscillation, and the Southern Annular Mode compared to conventional S-based SAI. Reduced changes in atmospheric circulation also translate to smaller perturbations in surface wind stress, ocean heat fluxes, and the Atlantic Meridional Overturning Circulation. Taken together, these findings highlight the potential of alternative materials for optimizing radiative efficacy of SAI, while minimizing atmospheric and oceanic side effects. This work will discuss the physical, chemical, and climatic implications of alternative SAI materials, bridging insights from microphysics to Earth system responses, as well as the underlying uncertainties.