Factories trigger local snowfall by freezing clouds - study

Industrial pollution can cause liquid clouds to turn into ice clouds in cold conditions, causing enough snowfall to cover an area larger than London in eight hours.  

A new study led by the University of Tartu and featuring contributions from partners including the University of Reading, suggests that man-made dust particles influence clouds by converting cloud droplets to ice crystals at temperatures between -10°C to -24°C, known as cloud glaciation. 
 
Published today (Friday, 15 November) in Science, the research highlights how a single glaciation event could produce up to 15 millimetres of snow to fall across an area spanning 2,200 km² - 600km² larger than the size of London. 
 
Professor Nicolas Bellouin, who co-authored the study from the University of Reading, said: “This finding matters a lot for people living near factories and industrial sites. We already knew about the health impacts of air pollution, but we now know that factory smoke can turn rain clouds into snow clouds when it's cold enough. This can cause unexpected snowfall that other areas don't get. A single event can dump over half an inch of snow across an area bigger than a city. This means communities downwind of factories might need to be better prepared for sudden snow, especially in winter." 
 
Powerplant snow 
 
Satellite observations revealed distinctive ice cloud formations and decreased cloud coverage in regions downwind of industrial centres across North America, Europe, and Asia. Researchers noticed special ice clouds forming and fewer liquid clouds in areas downwind of these sites.  
 
The research suggests that particles released from places like metal factories, cement plants, and oil refineries can cause liquid clouds to freeze and turn into snow. When snow fell during one particular glaciation event, it lasted for eight hours and covered an average area of 2,161 km² (about 834 square miles). 
 
The impact of factory pollution turning water clouds to ice clouds may also be significant for Earth’s climate. When glaciation happens, the clouds reflect 14% less sunlight back to space, which could lead to more warming. These changed clouds also release 4% more heat from Earth into space. The process also reduces cloud cover by 8% in affected areas.  
Reduced cloud cover is a local impact, however, and it remains unclear if man-made aerosols induce ice formation in clouds at larger scales. Further research is needed to understand the ability of various types of man-made aerosols to initiate the formation of ice. 

Toll et al 2024 Science “Glaciation of liquid clouds, snowfall, and reduced cloud cover at industrial aerosol hot spots". doi/10.1126/science.adl0303.

Images:

Top - stock image of snowfall in a residential area via Pixabay

Middle - The satellite image shows a plume of snow on the ground downwind of the Fokino cement plant in Russia. Via University of Tartu.

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