Preprints
https://doi.org/10.5194/acp-2020-965
https://doi.org/10.5194/acp-2020-965

  09 Nov 2020

09 Nov 2020

Review status: a revised version of this preprint was accepted for the journal ACP.

Robust winter warming over Eurasia under stratospheric sulfate geoengineering – the role of stratospheric dynamics

Antara Banerjee1,2, Amy H. Butler2, Lorenzo M. Polvani3, Alan Robock4, Isla R. Simpson5, and Lantao Sun6 Antara Banerjee et al.
  • 1Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA
  • 2National Oceanic and Atmospheric Administration, Chemical Sciences Laboratory, Boulder, CO, USA
  • 3Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA
  • 4Department of Environmental Sciences, Rutgers University, NJ, USA
  • 5Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 6Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA

Abstract. It has been suggested that increased stratospheric sulfate aerosol loadings following large, low latitude volcanic eruptions can lead to wintertime warming over Eurasia through dynamical stratosphere-troposphere coupling. We here investigate the proposed connection in the context of hypothetical future stratospheric sulfate geoengineering in the Geoengineering Large Ensemble simulations. In those geoengineering simulations, we find that stratospheric circulation anomalies that resemble the positive phase of the Northern Annular Mode in winter is a distinguishing climate response which is absent when increasing greenhouse gases alone are prescribed. This stratospheric dynamical response projects onto the positive phase of the North Atlantic Oscillation, leading to associated side-effects of this climate intervention strategy, such as continental Eurasian warming and precipitation changes. Seasonality is a key signature of the dynamically-driven surface response. We find an opposite response of the North Atlantic Oscillation in summer, when no dynamical role of the stratosphere is expected. The robustness of the wintertime forced response stands in contrast to previously proposed volcanic responses.

Antara Banerjee et al.

 
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Antara Banerjee et al.

Antara Banerjee et al.

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Short summary
We here find that simulated stratospheric sulfate geoengineering could lead to warmer Eurasian winters, alongside a drier Mediterranean and wetting to the north. These effects occur due to strengthening of the Northern Hemisphere stratospheric polar vortex, which shifts the North Atlantic Oscillation to a more positive phase. We find the effects in our simulations to be much more significant than the wintertime effects of large tropical volcanic eruptions, which inject much less sulfate aerosol.
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