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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 15, 9129-9141, 2015
https://doi.org/10.5194/acp-15-9129-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
18 Aug 2015
What is the limit of climate engineering by stratospheric injection of SO2?
U. Niemeier and C. Timmreck Max Planck Institute for Meteorology, Bundesstr. 53, 20146 Hamburg, Germany
Abstract. The injection of sulfur dioxide (SO2) into the stratosphere to form an artificial stratospheric aerosol layer is discussed as an option for solar radiation management. The related reduction of radiative forcing depends upon the injected amount of sulfur dioxide, but aerosol model studies indicate a decrease in forcing efficiency with increasing injection rate. None of these studies, however, consider injection rates greater than 20 Tg(S) yr−1. But 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 such a geoengineering method, expressed as the ratio between sulfate aerosol forcing and injection rate, decays exponentially. This result implies that the sulfate solar radiation management strategy required to keep temperatures constant at that anticipated for 2020, while maintaining business as usual conditions, would require atmospheric injections of approximately 45 Tg(S) yr−1 (±15 % or 7 Tg(S) yr−1) at a height corresponding to 60 hPa. This emission is equivalent to 5 to 7 times the Mt. Pinatubo eruption each year.

Citation: Niemeier, U. and Timmreck, C.: What is the limit of climate engineering by stratospheric injection of SO2?, Atmos. Chem. Phys., 15, 9129-9141, https://doi.org/10.5194/acp-15-9129-2015, 2015.
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Short summary
The injection of sulfur dioxide is considered as an option for solar radiation management. We have calculated the effects of SO2 injections up to 100 Tg(S)/y. Our calculations show that the forcing efficiency of the injection decays exponentially. This result implies that SO2 injections in the order of 6 times Mt. Pinatubo eruptions per year are required to keep temperatures constant at that anticipated for 2020, whilst maintaining business as usual emission conditions.
The injection of sulfur dioxide is considered as an option for solar radiation management. We...
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