Pollution from industrial hotspots can trigger ice formation in supercooled clouds, altering their reflective properties and increasing regional snowfall, according to a new study. The findings shed light on poorly understood impacts of anthropogenic aerosols on climate and could help improve climate modeling and mitigation strategies. The impact of human-generated aerosols (tiny air pollution particles) on climate, particularly in counteracting greenhouse gas-induced warming, remains uncertain. These aerosols, in addition to influencing cloud formation as cloud condensation nuclei (CCN), may also act as ice-nucleating particles (INPs), crucial for ice formation in supercooled liquid-water clouds at temperatures above -36 °degrees Celsius (°C). Anthropogenic INPs have been proposed to explain the plume-shaped snowfall patterns observed downwind of industrial sites, where emissions of heat, water vapor, and particles can influence cloud formation. However, a lack of observational evidence has prevented accurate assessment of the role of anthropogenic INPs in ice formation – or glaciation – of supercooled clouds and its potential impact on cloud cover and radiative fluxes. Using remote sensing data, including near-infrared satellite images from the satellite-based Moderate Resolution Imaging Spectroradiometer (MODIS) instrument, Velle Toll and colleagues observed the glaciation of supercooled clouds downwind of 67 aerosol-emitting industrial sites, such as metal and cement factories, paper mills, and powerplants. Toll et al. found that cloud glaciation from industrial aerosols, logged at various facilities in Canada and Russia, reduces solar radiation reflection by 13.7%, cloud cover by 8.3%, and cloud optical thickness by 18% while enhancing infrared radiance by 4.2% compared to unaffected clouds nearby. Additionally, the authors found that glaciation-induced snowfall greatly impacted local precipitation, with daily accumulations reaching up to 15 millimeters (mm), despite an average snowfall rate of 1.2 mm per hour, highlighting a measurable effect of industrial aerosols on localized snowfall patterns. The findings suggest that glaciation from anthropogenic ice-nucleating particles (INPs) could mirror the effects of pollution tracks in liquid clouds, highlighting the need for further investigation into the precise impact of anthropogenic INPs on cloud properties and climate. Additionally, rare glaciation events near nuclear power plants suggest factors other than INPs may also influence glaciation, such as local lofting of nearby aerosols by warm plumes.
