The presence of microplastics, tiny plastic fragments less than 5 millimeters in size, is now a constant even in the most remote and pristine corners of the Earth. From the ocean floors of Mariana Trench at snow-capped peaks of Everest, these particles are everywhere.
However, a study conducted by researchers at Pennsylvania State University, and published in ACSPublications, adds a disturbing piece to the picture: microplastics can alter cloud formation and, consequently, influence the global climate.
According to the study published on Environmental Science and Technology: Airmicroplastics they act as ice nucleating particlesi.e. microscopic nuclei that facilitate the formation of ice crystals in clouds. This process, known to atmospheric scientists, plays a crucial role in determining the behavior of clouds, which in turn influence meteorological phenomena such as rainfall and temperatures.
How microplastics change clouds
To understand the effect of microplastics, the Penn State team studied the ability to four types of plastic commonly found in the environment: low density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). The microplastics were suspended in small drops of water and cooled to observe how their presence affected the formation of ice.
The results are surprising: the average temperature at which the droplets froze it was 5-10 degrees higher than that of drops without microplastics. Under normal atmospheric conditions, a drop of water freezes at approximately -38°C.
However, the presence of impurities such as dust, bacteria or microplastics can lower this threshold, favoring the formation of ice at higher temperatures. “In the case of microplastics, 50% of the droplets were frozen at -22°C,” he explains Heidi Bussedoctoral student and lead author of the study.
Implications for climate and precipitation
The discovery has direct implications for weather and climate models. Miriam Freedmanprofessor of chemistry at Penn State and senior author of the study, clarifies that the presence of microplastics in the atmosphere it could already influence how clouds form and how they behave. “As air rises into the atmosphere and cools, microplastics can act as centers around which ice forms,” says Freedman.
This phenomenon could alter the distribution and frequency of precipitation. In a more polluted environment, microplastic particles distribute water among multiple cores, creating smaller droplets that delay rain. This means that clouds can store more water before releasing precipitationleading to more intense and sudden weather events.
Clouds themselves play a crucial role in the Earth’s heat balance. Depending on the altitude and composition, they can have a cooling effect, reflecting solar radiation, or a heating effect, retaining the heat emitted by the earth’s surface. The amount of liquid water and ice in a cloud greatly influences its ability to reflect or retain heat. If microplastics are altering this dynamic, it is likely that they are already contributing to climate change, although quantifying the impact is still a challenge.
The effect of environmental aging
The researchers also analyzed how the natural aging of microplastics – photochemical processes due to exposure to light, ozone and acids – can change their ability to nucleate ice. Generally, aging reduced the effectiveness of LDPE, PP and PET, while it increased the ability of PVC due to slight surface alterations.
These observations indicate that the complexity of the behavior of microplastics is influenced by environmental and chemical factorsadding an additional layer of uncertainty to climate models. According to Busse, “the life cycle of the plastics we use every day could alter the physical and optical properties of clouds, affecting the climate in ways we are only beginning to understand.”
Next steps
The implications of this finding require further study. The scientists also plan to examine the impact of chemical additives in plastics to determine whether their properties further modify the interaction with clouds.
As governments and global organizations search for solutions to reduce plastic in the environment, the scientific community continues to discover how profoundly these tiny particles are altering the world around us, even in the skies.
