Abstract
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.
Highlights
Climate engineering (CE) aims to counteract anthropogenic forcing due to greenhouse gas (GHG) emissions by reducing the amount of incoming solar radiation through solar radiation management (SRM)
A more comprehensive study, albeit two-dimensional, using a sectional aerosol microphysical model showed that the particle size distribution of the sulfate aerosol cloud depended strongly on the magnitude of the injections (Heckendorn et al, 2009) which has been confirmed by later studies (Pierce et al, 2010; Niemeier et al, 2011; Hommel and Graf, 2011; English et al, 2012)
In this study we aim to determine the efficiency of stratospheric SO2 injections and their dependency on the injection rate
Summary
Climate engineering (CE) aims to counteract anthropogenic forcing due to greenhouse gas (GHG) emissions by reducing the amount of incoming solar radiation through solar radiation management (SRM). To estimate the climate impact of SRM, model comparison studies have been performed (Kravitz et al, 2011) to simulate mirrors in space (e.g., Schmidt et al, 2012) or stratospheric injection of sulfur dioxide (e.g., Pitari et al, 2013). Such injections, first suggested by Budyko (1977) and later by Crutzen (2006), follow the example of volcanic eruptions that naturally emit large amounts of SO2 above the tropopause. These differences have implications for the estimated radiative forcing and the impact of the stratospheric aerosols on the climate and ozone concentration
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