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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-722
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
04 Aug 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Sensitivity of the radiative forcing by stratospheric sulfur geoengineering to the amount and strategy of the SO2 injection studied with the LMDZ-S3A model
Christoph Kleinschmitt1, Olivier Boucher2, and Ulrich Platt1 1Institute of Environmental Physics, Heidelberg University, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany
2Institut Pierre-Simon Laplace, CNRS/UPMC/Sorbonne Université, 4 Place Jussieu, 75252 Paris CEDEX 05, France
Abstract. The enhancement of the stratospheric sulfate aerosol layer has been proposed as a method of geoengineering to abate global warming. Previous modelling studies found that stratospheric aerosol injection could effectively compensate the warming by greenhouse gases on the global scale, but also that the achievable cooling effect per sulfur mass unit, i.e. the forcing efficiency, decreases with increasing injection rate. In this study we use the atmospheric general circulation model LMDZ with the sectional aerosol module S3A to determine how the forcing efficiency depends on the injected amount, the injection height and the spatio-temporal pattern of injection. We find that the forcing efficiency may decrease more drastically for larger SO2 injections than previously estimated. As a result, the net instantaneous radiative forcing does not exceed −2 W m−2 for continuous equatorial injections and it decreases (in absolute value) for the largest injection rates simulated (50 Tg S yr−1). In contrast to other studies, the net radiative forcing in our experiments is fairly constant with injection height (in a range 17 to 23 km) for a given amount of SO2 injected. Also spreading the SO2 injections between 30 °S and 30 °N or injecting only seasonally from varying latitudes does not result in a significantly larger (i.e. more negative) radiative forcing. Other key characteristics of our simulations include a consequent stratospheric heating caused by absorption of solar and infrared radiation by the aerosol, changes in stratospheric dynamics, with a collapse of the quasi-biennial oscillation at larger injection rates, which has impacts on the resulting spatial aerosol distribution, size and optical properties.

Citation: Kleinschmitt, C., Boucher, O., and Platt, U.: Sensitivity of the radiative forcing by stratospheric sulfur geoengineering to the amount and strategy of the SO2 injection studied with the LMDZ-S3A model, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-722, in review, 2017.
Christoph Kleinschmitt et al.
Christoph Kleinschmitt et al.
Christoph Kleinschmitt et al.

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Short summary
We use a state-of-the-art stratospheric aerosol model to study geoengineering through stratospheric sulfate aerosol injections. We find that the efficiency may decrease more drastically for larger injections than previously estimated and that injections at higher altitude are not more effective. This study may provide additional evidence that this proposed geoengineering technique is still more complicated, probably less effective and may implicate stronger side-effects than initially thought.
We use a state-of-the-art stratospheric aerosol model to study geoengineering through...
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