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

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 affect cloud feedback.
Specifically, we show that equilibrium climate sensitivity increases under
high aerosol concentration due to an increase in the short-wave cloud
feedback. The short-wave 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 possible connection between cloud feedback and
aerosol–cloud interactions.
