22 Aug 2022
22 Aug 2022
Status: this preprint is open for discussion.

Equilibrium climate sensitivity increases with aerosol concentration due to changes in rain efficiency

Guy Dagan Guy Dagan
  • Fredy and Nadine Herrmann Institute of Earth Sciences, Hebrew University, Jerusalem, Israel

Abstract. How Earth's climate reacts to anthropogenic forcing is one of the most burning questions faced by today’s scientific community. A leading source of uncertainty in estimating this sensitivity is related to the response of clouds. Under the canonical climate-change perspective of forcings and feedbacks, the effect of anthropogenic aerosols on clouds is categorized under the forcing component, while the modifications of the radiative properties of clouds due to climate change are considered in the feedback component. Each of these components contributes the largest portion of uncertainty to its relevant category and is largely studied separately from the other. In this paper, using idealized cloud resolving, radiative-convective-equilibrium simulations, with a slab ocean model, we show that aerosol-cloud interactions could significantly affect cloud feedback. Specifically, we show that equilibrium climate sensitivity increases under high aerosol concentration due to an increase in the shortwave cloud feedback. The shortwave cloud feedback is enhanced under high aerosol conditions due to a stronger increase in the precipitation efficiency with warming, which can be explained by higher sensitivity of the droplet size and the cloud water content to the CO2 concentration rise. These results indicate a strong connection between cloud feedback and aerosol-cloud interactions.

Guy Dagan

Status: open (until 25 Oct 2022)

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Guy Dagan

Guy Dagan


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Short summary
Using idealized simulations we demonstrate that the ECS, i.e., the increase in surface temperature under equilibrium conditions due to doubling of the CO2 concentration, increases with the aerosol concentration. The ECS increase is explained by a faster increase in precipitation efficiency with warming under high aerosol concentrations, which more efficiently depletes the water from the cloud and thus is manifested as an increase in the cloud feedback parameter.