Stratospheric geoengineering with black carbon aerosols

We used GISS ModelE, a general circulation model of Earth's climate, to simulate geoengineering with stratospheric black carbon aerosols. This allows us to compare the benefits and risks of using soot and sulfate for solar radiation management. Black carbon aerosols would cheaply and effectively cool the surface with very low development and deployment costs. 1 Tg of black carbon injected into the tropical lower stratosphere each year would result in global average cooling to approximately 1980 levels, which is several times less material than the amount of stratospheric sulfur needed to obtain the same amount of cooling. However, using soot aerosols would also have distinctly negative consequences, including alteration of the atmospheric thermal profile due to stratospheric heating, as well as catalytic ozone destruction, both of which contribute to a slowing of the general atmospheric circulation. The degree of cooling, as well as the magnitudes of the adverse effects, can be modified if one could change the initial particle size. Soot aerosol injection is relatively insensitive to the initial altitude of injection, due to heating and self-lofting of the particles. The creation of 1 Tg of black carbon particles from diesel fuel combustion would require large amounts of CO2 emissions, although the annual amount would be approximately 2 orders of magnitude lower than current global emissions.