Stratocumulus Adjustments to Aerosols Disentangled with a Causal Approach (Invited)

Aerosols can cause stratocumulus cloud brightening, thereby cooling the climate. Observations and models disagree on the magnitude of this cooling, partly because of the aerosol-induced liquid water path (LWP) adjustment, with climate models predicting an increase in LWP and satellites observing a weak decrease. With higher-resolution global climate models, which allow the simulation of mesoscale circulations in which stratocumulus clouds are embedded, there is hope to start bridging this gap. We present boreal summer-time simulations conducted with the ICOsahedral Non-hydrostatic (ICON) global storm-resolving model (GSRM). Compared to geostationary satellite data, this ICON set-up produces realistic cloud cover in the stratocumulus regions, but the mesoscale organization looks more cumuliform and the sign of LWP adjustments disagrees with observations. We investigate this disagreement with a causal approach, which combines time series with knowledge of cloud processes, allowing us to diagnose the sources of observation-model discrepancies. This also reveals the existence of confounding and selection biases that need to be considered for the analysis of coupled aerosol-cloud-meteorological systems, be they in stratocumulus cloud regions or in shallow and deep convective environments.