What is the limit of stratospheric sulfur climate engineering?

Abstract

Abstract. The injection of sulfur dioxide (SO2) into the stratosphere to form an artificial stratospheric aerosol layer is considered as an option for solar radiation management. The related reduction in radiative forcing depends upon the amount injected of sulfur dioxide but aerosol model studies indicate a decrease in forcing efficiency with increasing injection magnitude. None of these studies, however, consider injection strengths greater than 10 Tg(S) yr-1. This would be necessary to counteract the strong anthropogenic forcing expected if "business as usual" emission conditions continue throughout this century. To understand the effects of the injection of larger amounts of SO2 we have calculated the effects of SO2 injections up to 100 Tg(S) yr-1. We estimate the reliability of our results through consideration of various injection strategies, and from comparison with results obtained from other models. Our calculations show that the efficiency of the aerosol layer, expressed as the relationship between sulfate aerosol forcing and injection strength, decays exponentially. This result implies that the solar radiation management strategy required to keep temperatures constant at that anticipated for 2020, whilst maintaining "business as usual" conditions, would require atmospheric injections of the order of 45 Tg(S) yr-1 which amounts to 6 times that emitted from of the Mt. Pinatubo eruption each year.