Microplastics are turning up everywhere. We've found them in rivers, lakes, and oceans; in soil, snow and ice; in fish, whales, and us.
In recent years, we've even started to measure these tiny particles in the very air we breathe.
We still don't know what, if anything, that's doing to human health, but researchers in New Zealand suspect this pollution could have a real impact on our planet's climate if it grows bad enough.
"We studied how microplastic fragments and fibers – two types of microplastics commonly found in the atmosphere – interact with light, and used this information in a global climate model to calculate the overall impact of airborne microplastics on Earth's climate," explains atmospheric scientist Laura Revell from the University of Canterbury.
"Based on our assumptions, which were drawn from the limited number of airborne microplastics studies to date, the impact of airborne microplastics on climate is currently small, as expected."
But while that may hold true now, if airborne microplastics grow into a bigger problem in the future (which they seem on track to do), scientists are concerned they could possibly absorb, emit or scatter incoming sunlight and radiation to a much greater degree.
This could theoretically influence the climate on a global scale, similar to dust, ozone-destroying aerosols, or greenhouse gases, leading to a warming or cooling effect.
In the current study, researchers found non-pigmented microplastics in the lower atmosphere tend to scatter ultraviolet light and visible radiation, which is thought to have a cooling influence on surface climate.
However, these particles appear capable of absorbing infrared radiation, which is thought to have a warming effect on surface climate. What's more, they're absorbing UV at wavelengths that few other particles in Earth's atmosphere can take up.
"Microplastics may therefore contribute to the greenhouse effect," the authors conclude.
"Overall, microplastics predominantly scatter in the UV and visible regions as indicated by the single scattering albedo, whereas in the infrared they absorb radiation almost as much as they scatter it."
This is a concerning finding, and one that will need to be verified by far more research. Compared to microplastic studies on the ground, surprisingly little research has measured these tiny particles in the sky.
Back in 2019, researchers found microplastics buried in the soil of a remote section of the French Pyrenees. The sheer amount of pollution was what you'd expect to breathe in Paris, not in the dim and distinct peaks of a mountain range, which had the team wondering: How did the particles get there?
At the time, they suspected the pollution was being transported by currents in the atmosphere, which was a novel insight. If the authors were right, it meant microplastics were traveling vast distances via the wind.
Shortly afterwards, researchers at the United States Geological Survey found plastic was also raining down on the Rocky Mountains, adding more weight to the theory.
A few years later, researchers began reporting airborne microparticles in New Zealand, the United States, the United Kingdom, and China. The cities with the most airborne microplastics were London and Beijing, although it's hard to compare results as there isn't currently a standardized way to measure airborne plastics.
Most of the atmospheric pollution seemed to be coming from road dust, sea spray, and agricultural soil.
Once swept up into the air, models of our planet's atmosphere revealed these microplastics are traveling as far as Antarctica, raining down on some of the most remote areas of our planet. Direct sampling in the great southern continent has only affirmed that suspicion.
The discovery that microplastics have been blown up into the atmosphere and distributed around our planet is relatively new information, although given how ubiquitous, small and light these particles are, it's not altogether surprising.
Unfortunately, the increasing presence of plastic on our planet shows no signs of slowing down, which means we need to know how these floating microparticles are possibly impacting our health and our climate sooner rather than later.
After all, what is a minor problem now could very well grow into a much bigger issue later. Especially when you consider that the amount of plastic building up in our landfills and the environment is on track to double over the next three decades.
"Since plastic degrades through age and exposure to UV light to produce secondary microplastics, we expect microplastics to be present in Earth's atmosphere for many years to come," the authors conclude.
"In the absence of serious efforts to address microplastic pollution, mismanaged plastic waste could exert an influence on climate in the future."
The study was published in Nature.