Volcanic aerosols lend causality to the indicated substantial susceptibility of clouds to aerosol over global oceans

Abstract

The large indicated associations between aerosols and cloud radiative effects imply large negative radiative forcing, i.e., cooling incurred by the aerosols’ effects on clouds, if their relationships are causal. The alternative explanation is aerosol-meteorology co-variability. Here, we examine whether aerosols are the primary driver of aerosol-cloud co-variability, i.e., constituting susceptibility of the cloud properties to aerosols. It is done by domains affected by volcanic aerosols, where the aerosol-meteorology co-variability is expected to be minimized. We hypothesize that volcanic aerosols would reduce aerosol-meteorology co-variability under similar meteorology, thus diminishing aerosol-cloud co-variability. However, our findings in both volcanic and non-volcanic regions across the global oceans indicate a consistent pattern of aerosol-cloud co-variability. This does not prove definitively a causal link between aerosols and cloud properties, but mininimizes the probability that meteorological co-variability is a major cause.