Microbes make microplastics more likely to form ice in clouds, research reveals

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Tiny pieces of plastic, called microplastics, are showing up everywhere, even in the water in clouds, rain, and snow—and they may be affecting our weather and temperatures. A study published in Environmental Science & Technology and led by Hosein Foroutan, associate professor of civil and environmental engineering, found that microbes living on microplastics dramatically boost their ability to trigger ice formation in clouds.

In laboratory experiments, the microbial coating increased the temperature at which ice formed by about 6.5 degrees Celsius—a major shift in cloud physics.

"Microplastics are often thought of as a passive pollution," said Carrie Carpenter, a doctoral student in plant and environmental sciences and lead author on the paper. "But our research shows they can actually change how natural processes in the atmosphere work."

To understand this effect, the researchers recreated what happens in nature. They placed microscopic plastic particles in controlled laboratory conditions and allowed naturally occurring bacteria to attach and grow on their surfaces. Over several days, the microbes formed a thin layer called a biofilm—a sticky coating that helps microbes anchor themselves and survive.

Team members then tested how easily these particles could trigger freezing using a specialized setup that slowly cooled tiny droplets of water containing microplastics. By monitoring when each droplet froze, they could measure how effective the particles were at initiating ice formation.

The results revealed something especially surprising. Microbes attached to microplastics were even more effective at forming ice than the same microbes floating freely in water. In other words, the plastic surface enhanced the microbes' ice-making ability.

This suggests that microplastics don't just carry microbes through the atmosphere—they help amplify their environmental effects, highlighting a surprising link between human pollution and natural systems.

Plastic pollution's effect on precipitation

Why does this matter? Ice formation is a crucial step in how clouds develop and produce rain or snow. Anything that changes how ice forms can influence weather, precipitation patterns, and the ways clouds interact with sunlight and heat in the climate system.

"This means that plastic pollution could indirectly influence when and where rain or snow forms," said Carpenter. "And because clouds also regulate how much sunlight Earth reflects back to space and how much heat the atmosphere retains, changes in ice formation can also affect climate."

The researchers tested different types of microplastics, including polystyrene and polyethylene, in various sizes and under different conditions. Sunlight, heat, and aging alone did not significantly change how well the microplastics could form ice. But once microbes started growing on them, the particles became much better at making ice.

The size of the particles didn't affect their ice-making ability overall, but smaller microplastics had more "active sites" where ice could begin forming, according to the study. This means that the tiny living communities on microplastics—their "plastisphere"—play a key role in determining how these particles behave in the atmosphere, the study found.

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In some cases, this particle behavior could make clouds release rain or snow sooner. "Because clouds control both precipitation and how much sunlight the Earth's atmosphere absorbs or reflects, even small changes in cloud ice formation could influence regional weather patterns," said Foroutan.

That does not necessarily mean it will snow more everywhere, but rather that particles could alter cloud processes as more microplastics enter the atmosphere. By including this increase in microplastics in cloud formation and climate models, scientists will better understand its potential impact in the future.

"This study shows that microplastics are not just passive debris in the atmosphere," said Foroutan. "They serve as tiny platforms for microbial life, and together they can influence how clouds form and when precipitation occurs. This reveals a new and unexpected pathway by which human-generated pollution can interact with Earth's climate system."

Publication details

Lingzhi Chu et al, Finer Particulate Matter Exposure Disparities Exist but Vary across Pollution Concentrations, Environmental Science & Technology (2026). DOI: 10.1021/acs.est.5c06203

Journal information: Environmental Science & Technology

Key concepts

microplastic contaminationprecipitation (atmospheric)Climatic ProcessesWeather

Provided by Virginia Tech