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Discussion papers
https://doi.org/10.5194/acp-2019-1207
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1207
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Feb 2020

Submitted as: research article | 04 Feb 2020

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This preprint is currently under review for the journal ACP.

Climate-driven chemistry and aerosol feedbacks in CMIP6 Earth system models

Gillian Thornhill1, William Collins1, Dirk Olivié2, Alex Archibald3,4, Susanne Bauer5, Ramiro Checa-Garcia6, Stephanie Fiedler7, Gerd Folberth8, Ada Gjermundsen2, Larry Horowitz9, Jean-Francois Lamarque10, Martine Michou11, Jane Mulcahy8, Pierre Nabat11, Vaishali Naik9, Fiona M. O'Connor8, Fabien Paulot9, Michael Schulz2, Catherine E. Scott12, Roland Seferian11, Chris Smith12, Toshihiko Takemura13, Simone Tilmes10, and James Weber3 Gillian Thornhill et al.
  • 1Department of Meteorology, University of Reading, Reading, RG6 6BB, UK
  • 2Norwegian Meteorological Institute, Oslo, Norway
  • 3Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK
  • 4National Centre for Atmospheric Science, UK
  • 5NASA Goddard Institute for Space Studies, 2880 Broadway
  • 6IPSL/LSCE CEA-CNRS-UVSQ-UPSaclay UMR Gif sur Yvette, France
  • 7Max-Planck-Institute for Meteorology, Hamburg, 20146, Germany
  • 8Met Office Hadley Centre, Exeter, EX1 3PB, United Kingdom
  • 9GFDL/NOAA, Princeton University, Princeton, NJ 08540-6649
  • 10National Centre for Atmospheric Research, Boulder, CO, USA
  • 11Centre National de Recherches Météorologiques, Meteo-France, Toulouse Cedex, France
  • 12School of Earth and Environment, University of Leeds, Leeds, LS2 9JT
  • 13Research Institute for Applied Mechanics, Kyushu University, Fukuoka, Japan

Abstract. Feedbacks play a fundamental role in determining the magnitude of the response of the climate system to external forcing, such as from anthropogenic emissions. The latest generation of Earth system models include aerosol and chemistry components that interact with each other and with the biosphere. These interactions introduce a complex web of feedbacks which it is important to understand and quantify.

This paper addresses the multiple pathways for aerosol and chemical feedbacks in Earth system models. This is achieved by extending previous formalisms which include CO2 concentrations as a state variable to a formalism which in principle includes the concentrations of all climate-active atmospheric constituents. This framework is demonstrated by applying it to the Earth system models participating in CMIP6 with a focus on the non-CO2 reactive gases and aerosols (methane, ozone, sulphate aerosol, organic aerosol and dust).

We find that the overall climate feedback through chemistry and aerosols is negative in the CMIP6 Earth system models due to increased negative forcing from aerosols with warmer temperatures. Through diagnosing changes in methane emissions and lifetime we find that if Earth system models were to allow methane to vary interactively, methane positive feedbacks (principally wetland methane emissions and biogenic VOC emissions) would offset much of the aerosol feedbacks.

Gillian Thornhill et al.

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Latest update: 18 Feb 2020
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Short summary
We find that increased temperatures affect aerosols and reactive gases, by changing natural emissions and their rates of removal from the atmosphere. Changing the composition of these species in the atmosphere affects the radiative budget of the climate system and therefore amplifies or dampens the climate response of climate models of the Earth System. This study find the largest effect is a dampening of climate change as warmer temperatures increase the emissions of cooling aerosols.
We find that increased temperatures affect aerosols and reactive gases, by changing natural...
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