Understanding and Modeling the Interactions Between Sulfate Geoengineering and Clouds

[Andrew Lockley]

https://ams.confex.com/ams/101ANNUAL/meetingapp.cgi/Paper/379262

Understanding and Modeling the Interactions Between Sulfate Geoengineering and Clouds (Invited Presentation)

Friday, January 15, 2021

3:30 PM - 3:35 PM

Abstract

The artificial injection of SO2 into the stratosphere (sulfate geoengineering, SG) has been proposed as a way to partially reduce surface temperatures. Numerous side effects of such an intervention have been explored in climate models simulations, both in the stratosphere (i.e. changes in stratospheric dynamics, stratospheric ozone loss) and at the surface (i.e. changes in the hydrological cycle, shifts in seasonal temperature cycles).

Changes in cloud cover would be an important factor in an overall assessment of SG for multiple reasons: mainly, their importance in our planet's radiation balance indicates that SG-cloud interactions would determine how efficient a given injection might be in lowering surface temperatures. Changes in cloud coverage might also reduce or increase diffuse radiation reaching the surface, thus affecting different ecosystems in different ways.

The overall response of clouds to SG could be driven by multiple factors, for instance changes in the vertical temperature gradient, sulfate particles settling down from the stratosphere interacting with cloud nucleation processes, shifts in the Intertropical Convergence Zone or in the Walker Circulation or changes in inter-hemispheric and equator-to-pole temperature gradient, and might affect different types of clouds.

Furthermore, since cloud dynamics are very dependant on small-scale processes, in the global climate models used to study SG scenarios the processes that lead to clouds formation are parametrized as a function of the large-scale conditions. While the response of these parametrizations can be validated against observations in normal conditions, this can't happen in the presence of a large, sustained SG perturbation for which even past volcanic eruptions might not be a good analogue. Therefore, the possibility exists that not all cloud changes observed in climate models as a response to SG are realistic.

Using both previous findings available in the scientific literature and novel simulations, an overview of our knowledge so far of how and why clouds would change under SG conditions is presented, together with an assessment of the importance of these changes. Finally, some suggestions for areas of future research related to aerosol-cloud interactions in the context of sulfate geoengineering are given.

author

Daniele Visioni

Cornell University

Ithaca, NY