Preprints
https://doi.org/10.5194/acp-2021-133
https://doi.org/10.5194/acp-2021-133

  09 Mar 2021

09 Mar 2021

Review status: this preprint is currently under review for the journal ACP.

Identifying the sources of uncertainty in climate model simulations of solar radiation modification with the G6sulfur and G6solar Geoengineering Model Intercomparison Project (GeoMIP) simulations

Daniele Visioni1, Douglas G. MacMartin1, Ben Kravitz2,3, Olivier Boucher4, Andy Jones5, Thibaut Lurton4, Michou Martine6, Michael J. Mills7, Pierre Nabat6, Ulrike Niemeier8, Roland Séférian6, and Simone Tilmes7 Daniele Visioni et al.
  • 1Sibley School for 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
  • 4Institut Pierre-Simon Laplace, Sorbonne Université/CNRS, Paris, France
  • 5Met Office Hadley Centre, Exeter, EX1 3PB, UK
  • 6CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 7Atmospheric Chemistry, Observations, and Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 8Max Planck Institute for Meteorology, Hamburg, Germany

Abstract. We present here results from the Geoengineering Model Intercomparison Project (GeoMIP) simulations for the experiment G6sulfur and G6solar for six Earth System Models participating in the Climate Model Intercomparison Project (CMIP) Phase 6. The aim of the experiments is to reduce the warming from that resulting from a high-tier emission scenario (Shared Socioeconomic Pathways SSP5-8.5) to that resulting from a medium-tier emission scenario (SSP2-4.5). These simulations aim to analyze the response of climate models to a reduction in incoming surface radiation as a means to reduce global surface temperatures, and they do so either by simulating a stratospheric sulfate aerosol layer or, in a more idealized way, through a uniform reduction in the solar constant in the model. We find that, by the end of the century, there is a considerable inter-model spread in the needed injection of sulfate (29 ± 9 Tg-SO2/yr between 2081 and 2100), in how the aerosol cloud is distributed latitudinally, and in how stratospheric temperatures are influenced by the produced aerosol layer. Even in the simpler G6solar experiment, there is a spread in the needed solar dimming to achieve the same global temperature target (1.91 ± 0.44 %). The analyzed models already show significant differences in the response to the increasing CO2 concentrations for global mean temperatures and global mean precipitation (2.05 K ± 0.42 K and 2.28 ± 0.80 %, respectively, for the SSP5-8.5-SSP2-4.5 difference between 2081 and 2100): the differences in the simulated aerosol spread then change some of the underlying uncertainty, for example in terms of the global mean precipitation response (−3.79 ± 0.76 % for G6sulfur compared to −2.07 ± 0.40 % for G6solar against SSP2-4.5 between 2081 and 2100). These differences in the aerosols behavior also result in a larger inter-model spread in the regional response in the surface temperatures in the case of the G6sulfur simulations, suggesting the need to devise various, more specific experiments to single out and resolve particular sources of uncertainty. The spread in the modelled response suggests that a degree of caution is necessary when using these results for assessing specific impacts of geoengineering in various aspects of the Earth system: however, all models agree that, compared to a scenario with unmitigated warming, stratospheric aerosol geoengineering has the potential to both globally and locally reduce the increase in surface temperatures.

Daniele Visioni et al.

Status: open (until 04 May 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-133', Peter Irvine, 23 Mar 2021 reply
  • RC2: 'Comment on acp-2021-133', Anonymous Referee #2, 08 Apr 2021 reply

Daniele Visioni et al.

Daniele Visioni et al.

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Short summary
A new set of simulations from various climate models is used here to investigate sources of uncertainty and model differences when simulating the injection of SO2 in the stratosphere in order to mitigate the effects of climate change (geoengineering). The way in which different models simulate the aerosols and their spread around the stratosphere is a large factor in determining this. Overall, models agree that aerosols have the potential to mitigate the warming produced by greenhouse gases.
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