Stratospheric Albedo Modification by Aerosol Injection

This paper reviews and develops the proposal, widely discussed but not examined in detail, to use stratospheric aerosols to increase the Earth's albedo to Solar radiation in order to control climate change. The potential of this method has been demonstrated by the "natural experiments" of volcanic injection of sulfate aerosols into the stratosphere that led to subsequent observed global cooling. I consider several hygroscopic oxides as possible aerosol materials in addition to oxides of sulfur. Aerosol chemistry, dispersion and transport have been the subject of little study and are not understood, representing a significant scientific risk. Even the optimal altitude of injection and aerosol size distribution are poorly known. Past attention focused on guns and airplanes as means of lofting aerosols or their chemical precursors, but large sounding rockets are cheap, energetically efficient, can be designed to inject aerosols at any required altitude, and involve little technical risk. Sophisticated, mass-optimized "engineered" particles have been proposed as possible aerosols, but the formidable problems of their production in quantity, lofting and dispersion have not been addressed.