Anthropogenic aerosols turn liquid cloud droplets into ice crystals, produce snow and eat holes in the clouds

Living downwind of a cement-producing or a metallurgical plant could mean you get more snow, fewer clouds and more sunshine compared to nearby areas. We use satellite observations to reveal the glaciation of supercooled stratiform liquid-phase clouds by anthropogenic aerosols acting as ice-nucleating particles. There are strong indications that glaciation is caused by aerosols emitted from oil refineries, coal-fired power plants, cement, metal smelting and processing, chemical plants, and other anthropogenic air pollution sources in Europe, Asia, North America and Australia. Heavily polluted areas derived by simulating aerosol dispersion from strong anthropogenic aerosol point sources overlap with the areas of glaciation, snowfall, and decreased cloud cover strikingly well. Moreover, the polluted areas with decreased cloud cover are plume-shaped, with a distinctive head pointing towards the pollution source, similar to aerosol-polluted cloud tracks in liquid-water clouds (Toll et al 2019 Nature https://doi.org/10.1038/s41586-019-1423-9).

Glaciation-induced snowfall downwind of aerosol sources is observed using ground-based precipitation radars, and tracks of snow are also seen on the ground in satellite imagery. Aerosol-induced glaciation and snowfall lead to reduced cloud cover. At multiple aerosol sources, glaciation events are more frequent than polluted tracks in liquid-phase clouds. Thus, at least locally at some aerosol sources in the middle and high latitudes, the warming effect induced by aerosols acting as ice-nucleating particles likely exceeds the cooling effect induced by aerosols acting as cloud condensation nuclei. Further research is needed to quantify the global radiative forcing by anthropogenic ice nucleating particles.