Friday, November 15, 2024

Industrial snow: Factories trigger local snowfall by freezing clouds

Estonian Research Council

video:
Weather radar images show a plume of snow downwind of the Rouyn-Noranda copper smelter in Canada. The weather radar is located near Landrienne, Canada.
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Credit: V. Toll, et al

Anthropogenic aerosols, tiny solid and liquid air pollution particles, have masked a fraction of global warming caused by anthropogenic greenhouse gases. Climate researchers have known for decades that anthropogenic aerosols perturb liquid clouds by enabling the formation of a larger number of cloud droplets, making clouds brighter. A new landmark study led by the University of Tartu suggests that anthropogenic aerosols may also influence clouds by converting cloud droplets to ice at temperatures below zero degrees Celsius.

Powerplant Snow

Using satellite observations, climate researchers discovered unique plumes of ice clouds and reduced cloud cover downwind of industrial hot spots in North America, Europe and Asia. Moreover, ground-based precipitation radar data revealed plumes of snowfall in the same areas where reduced cloud cover was observed in satellite images. Combining satellite and ground-based radar observations, researchers traced the physical processes from the formation of ice to snowfall to reduced cloud cover downwind of industrial hot spots. The lead author of the study, Assoc Prof V. Toll from the University of Tartu, highlighted that collaboration among researchers with diverse expertise was essential for developing the physical understanding of the identified anthropogenic snowfall events.

Supercooled Water

Water freezes at zero degrees Celsius, right? In fact, cloud droplets can stay liquid down to temperatures as low as about -40 degrees Celsius, known as the supercooling of water. This is because suitable aerosol particles are needed to convert cloud droplets to ice at temperatures between zero and -40 degrees Celsius. The study suggests that industries such as metallurgical and cement factories, coal-fired power plants, and oil refineries emit aerosol particles that cause freezing of supercooled liquid clouds, leading to snowfall. However, it is important to note that heat and water vapour emitted by industries may also play a role in the freezing of supercooled liquid clouds.

The discovered plumes of reduced cloud cover are local phenomena, and it remains unclear if anthropogenic aerosols induce ice formation in clouds at larger spatial scales. Further research is needed to understand the ability of various types of anthropogenic aerosols to initiate the formation of ice.

Journal

Science

DOI

10.1126/science.adl0303

Method of Research

Imaging analysis

Subject of Research

Not applicable

Article Title

Glaciation of Liquid Clouds, Snowfall, and Reduced Cloud Cover at Industrial Aerosol Hot Spots

Article Publication Date

15-Nov-2024

The weather radar image shows a plume of snow downwind of the Rouyn-Noranda copper smelter in Canada. The weather radar is located near Landrienne, Canada.

The satellite image shows a plume of reduced cloud cover downwind of the Rouyn-Noranda copper smelter in Canada.

Observations of reduced cloud cover and snowfall downwind of industrial air pollution hotspot

The satellite image shows a plume of snow on the ground downwind of the Fokino cement plant in Russia.

Industrial air pollution triggers ice formation in clouds, reducing cloud cover and boosting snowfall

Summary author: Walter Beckwith

American Association for the Advancement of Science (AAAS)

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.