13 Jun 2022
13 Jun 2022

Climate response to off-equatorial stratospheric sulfur injections in three Earth System Models – Part 1: experimental protocols and surface changes

Daniele Visioni1, Ewa M. Bednarz1, Walker R. Lee1, Ben Kravitz2,3, Andy Jones4, Jim M. Haywood4,5, and Douglas G. MacMartin1 Daniele Visioni et al.
  • 1Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY, USA
  • 2Department of Earth and Atmospheric Science, Indiana University, Bloomington, IN, USA
  • 3Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA
  • 4Met Office Hadley Centre, Exeter, UK
  • 5College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK

Abstract. There is now a substantial literature of climate model studies of equatorial or tropical stratospheric SO2 injections that aim to counteract the surface warming produced by rising concentrations of greenhouse gases. Here we present the results from the first systematic intercomparison of climate responses in three Earth System Models where the injection of SO2 occours at different latitudes in the lower stratosphere. Our aim is to determine commonalities and differences between the climate model responses in terms of the distribution of the optically reflective sulfate aerosols produced from the oxidation of SO2, and in terms of the surface response to the resulting reduction in solar radiation. A focus on understanding the contribution of characteristics of models transport alongside their microphysical and chemical schemes, and on evaluating the resulting stratospheric responses in different models is given in the companion paper (Bednarz et al., 2022). The goal of this exercise is not to evaluate these single point injection simulations as stand-alone proposed strategies to counteract global warming; instead we determine sources and areas of agreement and uncertainty in the simulated responses and, ultimately, the possibility of designing a comprehensive intervention strategy capable of managing multiple simultaneous climate goals through the combination of different injection locations. We find large disagreements between GISS-E2.1-G and the CESM2-WACCM6 and UKESM1.0 models regarding the magnitude of cooling per unit of aerosol optical depth (AOD) produced, from 4.7 K per unit of AOD in CESM2-WACCM6 to 16.7 K in the GISS-E2.1-G version with modal aerosol microphysics. By normalizing the results with the global mean response in each of the models, and thus assuming that the amount of SO2 injected is a free parameter that can be managed independently, we highlight some commonalities in the overall distributions of the aerosols, in the inter-hemispheric surface temperature response and in shifts to the Inter-Tropical Convergence Zone, and also some areas of disagreement, such as the aerosol confinement in the equatorial region and the transport to polar latitudes.

Daniele Visioni et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-401', Anonymous Referee #1, 18 Jul 2022
    • AC1: 'Reply on RC1', Daniele Visioni, 14 Sep 2022
  • RC2: 'Comment on egusphere-2022-401', Anonymous Referee #2, 02 Aug 2022
    • AC2: 'Reply on RC2', Daniele Visioni, 14 Sep 2022

Daniele Visioni et al.

Daniele Visioni et al.


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Short summary
The paper constitutes part 1 of a study performing a first systematic inter-model comparison of the atmospheric responses to stratospheric sulfate aerosol injections (SAI) at various latitudes as simulated by three state-of-the-art Earth System Models. We identify similarities and differences in the modelled aerosol burden and investigate the differences in the aerosol approaches between the models, and ultimately show the differences produced in surface climate, temperature and precipitation.