The more we learn about plastic, the more we find it everywhere. Research has shown that tiny microplastic particles litter the world’s oceans and rivers, from the Arctic and Antarctic. Microplastics are in the soils where fruits and vegetables grow. They’re found in the internal organs of wildlife. Scientists have even detected plastic in human blood, brains and placentas.

A growing body of research has also shown that microplastics — particles less than 5 millimeters, or about 0.2 inches, in size — are being blown up into the atmosphere by wind and sea spray, then falling from the sky in rain. So it would only make sense that plastic is also present in clouds.

Which is exactly what a new study in Environmental Chemistry Letters has found. Researchers collected cloud water samples from high-altitude mountains in Japan — including the summit of Mount Fuji — and discovered small airborne particles from nine different types of plastics. This finding led the scientists to suggest that high-altitude microplastics could influence cloud formation and therefore, alter the climate. However, they did not investigate these possibilities in the current study.

The scientists collected the cloud water samples using fine wire devices and then used imaging techniques to analyze the samples. They detected microplastics in the cloud water ranging in diameter from 7.1 to 94.6 micrometers — sizes hardly or even impossibly perceptible to the naked eye. Nine different types of plastic were detected, including, among others, polyethylene, polypropylene and polyethylene terephthalate — common forms of plastic used to make drink bottles, shopping bags, toys and synthetic clothing.

Each liter of cloud water examined contained between 6.7 and 13.9 microplastics. However, the team argues that these numbers are likely underestimated since some plastic particles could have been trapped in the wire and tubing of the collection devices.

The researchers think that some clouds would contain more microplastics than others — specifically, clouds that formed over the ocean.

“It is possible that ocean microplastics are dispersed into the atmosphere and transported to the top of Mount Fuji,” lead author Hiroshi Okochi, a professor at Waseda University, told Mongabay in an email. He added that his team’s observations also showed that the clouds examined held higher concentrations of polypropylene when typhoons approached.

So, how might microplastics contribute to — and alter — the natural formation of clouds?

Plastics are known to be hydrophobic, meaning they repel water. But they can become hydrophilic — attracting water — when sunlight degrades them, or when organic matter adheres to their surfaces. Once microplastics become hydrophilic, the researchers say they may act as “cloud condensation nuclei,” with droplets of moisture forming around the tiny plastic particles, which then aggregate to make a cloud. Or they may be part of “ice nucleus particles,” molecules that form ice crystals in the atmosphere.

These cloud-forming microplastics could even influence Earth’s climate, according to the researchers — though precisely what effect they might have is unknown.

“If AMPs [airborne microplastics] form more clouds, they reflect more sunlight,” Okochi said. “This is called the indirect radiation effect, and it has the effect of cooling the earth.”

“On the other hand, the strong ultraviolet rays in the upper atmosphere … accelerate the degradation of AMPs, and it has been pointed out that AMPs may release greenhouse gases such as methane and carbon dioxide,” he added. “This has the effect of warming the earth.”

Denise Mitrano, an environmental analytical chemist at ETH Zürich, who was not involved in this research, said the study presents a “unique data set” that fills in some knowledge gaps about the distribution of microplastics. However, she said the authors’ suggestion about microplastics forming clouds may not be entirely right. That’s because the presence of microplastics in a cloud could simply mean the particles are “being transported with the air mass and not necessarily influencing the cloud” formation process itself, Mitrano told Mongabay in an emailed statement.

In a recent perspective piece published in Nature Geoscience, Mitrano and co-authors suggested that only the smallest microplastics and nanoplastics — plastic pieces less than 100 nanometers — had the potential to influence cloud formation directly. Additionally, they said cloud formation depends on several factors, such as how weathered the plastic is and whether large amounts of plastics are present compared with other particles or aerosols.

“In our perspective [piece], we did not suggest that atmospheric microplastics would have an overall impact on climate — especially in relation to the clear impacts of other anthropogenic stressors and greenhouse gas emissions — but rather, in some cases, nano- and microplastics may impact cloud formation where there are comparatively fewer aerosols in the atmosphere, which may subsequently influence reflected radiation,” Mitrano said.

“The next steps in this line of research would be to also conduct laboratory tests to understand if/how different nano- and microplastics can influence cloud formation processes,” she added, “and what this is dependent on.”

Considering the huge unknowns, the need to do this research carries considerable urgency with it: Between the 1950s and 2015, humanity generated 6.3 billion metric tons of plastic waste; based on current trends, that total is expected to soar to 26 billion metric tons by 2050. How all that plastic will impact Earth’s operating systems, wildlife and humanity is still an open question.

Elizabeth Claire Alberts is a senior staff writer for Mongabay. Follow her on Twitter @ECAlberts.

Banner image: Clouds over mountains in Japan. Image by Raita Futo via Flickr (CC BY 2.0).

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Citations:

Wang, Y., Okochi, H., Tani, Y., Hayami, H., Minami, Y., Katsumi, N., … Niida, Y. (2023). Airborne hydrophilic microplastics in cloud water at high altitudes and their role in cloud formation. Environmental Chemistry Letters, 21(6), 3055-3062. doi:10.1007/s10311-023-01626-x

Aeschlimann, M., Li, G., Kanji, Z. A., & Mitrano, D. M. (2022). Potential impacts of atmospheric microplastics and nanoplastics on cloud formation processes. Nature Geoscience, 15(12), 967-975. doi:10.1038/s41561-022-01051-9