28 Feb 2023
 | 28 Feb 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Comment on “An approach to sulfate geoengineering with surface emissions of carbonyl sulfide” by Quaglia et al. (2022) 

Marc von Hobe, Christoph Brühl, Sinikka T. Lennartz, Mary E. Whelan, and Aleya Kaushik

Abstract. Solar radiation management through artificially increasing the amount of stratospheric sulfate aerosol is being considered as a possible climate engineering method. To overcome the challenge of transporting the necessary amount of sulfur to the stratosphere, Quaglia and co-workers suggest deliberate emissions of carbonyl sulfide (OCS), a long-lived precursor of atmospheric sulfate. In their paper, published in Atmospheric Chemistry and Physics in 2022, they outline two scenarios with OCS emissions either at the Earth’s surface or in the tropical upper troposphere and calculate the expected radiative forcing using a climate model. In our opinion, the study (i) neglects a significantly higher surface uptake that will inevitably be induced by the elevated atmospheric OCS concentrations and (ii) overestimates the net cooling effect of this OCS geoengineering approach due to some questionable parameterizations and assumptions in the radiative forcing calculations. In this commentary, we use state of the art models to show that at the mean atmospheric OCS mixing ratios of the two emissions scenarios, the terrestrial biosphere and the oceans are expected to take up more OCS than is being released to reach these levels. Using chemistry climate models with a long-standing record for estimating the climate forcing of OCS and stratospheric aerosols, we also show that the net radiative forcing of the emission scenarios suggested by Quaglia and co-workers is smaller than suggested and insufficient to offset any significant portion of anthropogenically induced climate change. Our conclusion is that a geoengineering approach using OCS will not work under any circumstances and should not be considered further.

Marc von Hobe et al.

Status: open (until 11 Apr 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-268', Daniele Visioni, 01 Mar 2023 reply
  • RC2: 'Comment on egusphere-2023-268', Anonymous Referee #2, 29 Mar 2023 reply

Marc von Hobe et al.

Marc von Hobe et al.


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Short summary
Carbonyl sulfide plays a role in the climate system as a greenhouse gas and as the major non-volcanic precursor of particles reflecting sunlight. Here we comment on a proposal to increase the number of particles by emitting extra carbonyl sulfide at the surface. We show that the balance between aerosol cooling and greenhouse gas warming may not be as favorable as suggested, and also that much of the carbonyl sulfide emissions will actually be taken up by the biosphere and the oceans.