http://onlinelibrary.wiley.com/doi/10.1002/2013JD020566/abstract
Keywords: Geoengineering;Intercomparison;Ozone Abstract [1] Geoengineering with stratospheric sulfate aerosols has been proposed as a means of temporarily cooling the planet, alleviating some of the side effects of anthropogenic CO2 emissions. However, one of the known side effects of stratospheric injections of sulfate aerosols under present-day conditions is a general decrease in ozone concentrations mainly via changes in photolysis rates, tropical upwelling of ozone-poor air, and an increase in available surfaces for heterogeneous chemistry. Here we present the effects that increased amounts of sulfate aerosol have on stratospheric meteorology and/or ozone concentrations, as simulated by two general circulation models and two coupled chemistry-climate models within the experiments G3 and G4 of the Geoengineering Model Intercomparison Project (GeoMIP). On average, the models simulate in G4 a factor of 20-40 increase in sulfate aerosol surface area density at 50 hPa in the tropics with respect to unperturbed background conditions and a factor of 3-10 increase at mid- and high latitudes, similar to conditions a year after the Mt. Pinatubo eruption. The net effect on ozone concentrations during the central decade of the experiment (2040-2049) is a decrease in globally averaged ozone by 1.1-2.1 DU for all models except for GISS-E2-R, which shows a decrease by about 9.7 DU in experiment G4. Enhanced heterogeneous chemistry on sulfate aerosols leads to an ozone increase in low and mid-latitudes, which is not included in the GISS-E2-R model, whereas enhanced heterogeneous reactions in polar regions (both on sulfate and polar stratospheric cloud particles) and increased tropical upwelling lead to a reduction of stratospheric ozone. The increase in UV-B radiation at the surface due to ozone depletion is offset by the screening due to the aerosols in the tropics and mid-latitudes, while in polar regions the UV-B radiation is increased by 5% on average, with 12% peak increases during springtime. The contribution of ozone changes to the tropopause radiative forcing during 2040-2049 is found to be less than -0.1 W m-2 for all models and experiments, except for GISS-E2-R in G4 (-0.23 W m-2). After 2050, because of decreasing ClOx concentrations, the suppression of the NOx cycle becomes more important than destruction of ozone by ClOx, causing an increase in total stratospheric ozone. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/groups/opt_out.
