Large‐Scale Industrial Cloud Perturbations Confirm Bidirectional Cloud Water Responses to Anthropogenic Aerosols

Abstract:

It is unknown to what extent the global cooling effect of anthropogenic aerosols offsets the warming effect of anthropogenic greenhouse gases. The strength of the aerosol climate cooling effect exerted through changes in the properties of clouds is especially uncertain. In this research, we extend satellite observations of polluted cloud tracks from Toll et al. (2019, Nature, https://doi.org/10.1038/s41586-019-1423-9) with analysis of larger scale polluted cloud areas detected in MODerate-resolution Imaging Spectroradiometer satellite images. We demonstrate that large-scale anthropogenic aerosol-induced cloud perturbations exist at various major industrial aerosol source regions. The areal extent of the polluted cloud areas detected in MODIS satellite images extended to hundreds by hundreds of kilometres. Polluted clouds detected in satellite images in the global anthropogenic air pollution hot spot of Norilsk, Russia, and in other regions show that aerosol-induced cloud water increases and decreases compensate each other at large spatial scales similarly to ship-track-like perturbations (Trofimov et al 2020, JGR Atmospheres, https://doi.org/10.1029/2020JD032575). On average, there is relatively weak decrease in cloud water in the large areas with strong decreases in cloud droplet radii. In Norilsk cloud perturbations the decrease in LWP offsets 3 % of the radiative forcing through the Twomey effect on average. This is in very good agreement with the previous results based on small-scale polluted cloud tracks and strongly disagrees with unidirectionally increased liquid water path in global climate models. We expect that our results will lead to improved physical parameterizations in general circulation models and more reliable projections of the future climate.