Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2017-107
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
07 Feb 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Radiative and climate effects of stratospheric sulfur geoengineering using seasonally varying injection areas
Anton Laakso1,2, Hannele Korhonen3, Sami Romakkaniemi1, and Harri Kokkola1 1Finnish Meteorological Institute, Atmospheric Research Centre of Eastern Finland, Kuopio, FI-70200, Finland
2Department of Soil, Water and Climate, University of Minnesota, Twin Cities, St. Paul, MN-55108, Minnesota, USA
3Finnish Meteorological Institute, Climate Research, Helsinki, FI-00100, Finland
Abstract. Stratospheric sulfur injections have often been suggested as a cost effective geoengineering method to prevent or slow down global warming. In geoengineering studies these injections are commonly targeted to the equator, where the intensity of the solar radiation is highest. However, it may not be the most optimal aerosol injection strategy because the radiative forcing concentrating over the equator decreases the meridional temperature gradient. In this study we employ alternative aerosol injection scenarios to investigate if the resulting radiative forcing can be optimized to be zonally more uniform without decreasing the global efficacy. We used a global aerosol-climate model together with an Earth system model to study the radiative and climate effects of stratospheric sulfur injection scenarios with different injection areas. According to our simulations, varying the SO2 injection area seasonally would result in a similar global mean cooling effect as injecting SO2 to the equator, but with a more uniform zonal distribution of shortwave radiative forcing. Compared to the case of equatorial injections, in the optimized injection scenario where the maximum sulfur production from injected SO2 followed the maximum of solar radiation, the shortwave radiative forcing decreased by 27 % over the equator (between the latitudes between 20° N and 20° S) and increased by 15 % over higher latitudes. Compared to the continuous injections to equator, in summer months the radiative forcing was increased by 17 % and 14 % and winter months decreased by −14 % and −16 % at northern and southern hemispheres respectively. However, these forcings do not translate into very significant changes in temperatures. Based on ESM simulations, changes in forcing would lead only to 0.05 K warmer winters and 0.05 K cooler summers at the northern hemisphere which is roughly 3 % of the cooling resulted from solar radiation management scenarios studied here. At the same time the meridional temperature gradient was better maintained.

Citation: Laakso, A., Korhonen, H., Romakkaniemi, S., and Kokkola, H.: Radiative and climate effects of stratospheric sulfur geoengineering using seasonally varying injection areas, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-107, in review, 2017.
Anton Laakso et al.
Anton Laakso et al.
Anton Laakso et al.

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Short summary
Based on simulations, equatorial stratospheric sulfur injections have shown to be efficient strategy to counteract the ongoing global warming. However, equatorial injections would result into relatively larger cooling in low latitudes than in high latitudes. This together with greenhouse gas induced warming would lead to cooling in the equator and warming in the high latitudes. Results of this study show that more optimal cooling effect is achieved by varying the injection area seasonally.
Based on simulations, equatorial stratospheric sulfur injections have shown to be efficient...
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