Microplastics are absorbing heat in the atmosphere and contributing to global warming, a new study reveals.

Microplastics are infamous for being everywhere, contaminating ecosystems and accumulating inside our bodies. Scientists have known for a while that plastics are also blown high into the atmosphere, where they are now pervasive, but it was unclear what impact they might be having up there.

Study co-author Drew Shindell, a distinguished professor of Earth science at Duke University, told Live Science that the climate change impact of plastic particles is fairly small ‪—‬ comparable to the emissions of a small country. In numbers, this is the equivalent of around a couple of percent of the contribution from carbon dioxide (CO₂) — the main driver of climate change — or a couple hundredths of a degree of warming. However, the researchers' modeling was based on a limited understanding of the amount of plastic in the atmosphere, so the extent of the warming effect is uncertain.

"The key finding is really that the warming strongly outweighs the cooling," Shindell said. "I think we have a lot of confidence in that because we did all of these measurements in the laboratory of how [microplastics and nanoplastics] interact with sunlight. What we don't have so much confidence in and what's still a big uncertainty is exactly how many of these are in the atmosphere."

Microplastics come from larger plastic debris that breaks up and from plastic products that are designed to be microscopic in the first place, such as the tiny beads used in some facial scrubs and shower gels. A plastic is classified as a microplastic when it has a width of 1 micrometer to 5 millimeters (0.00004 to 0.2 inches). Anything less than 1 micrometer is classified as a nanoplastic.

To better understand how different colors of microplastic and nanoplastic particles behave, Shindell's colleagues in Shanghai collected plastic debris and studied its reaction to sunlight and radiation. They also checked whether very light colors would darken in the atmosphere over time ‪—‬ and found that they did.

"Sometimes if you get a parking pass or something that you put on your windshield, the plastic yellows with time because it's out in the sunlight," Shindell said. "We thought maybe particles of plastic do that, too."

Once the team understood how the plastic particles behaved, Shindell and his colleagues in the U.S. used that data alongside data on plastic emissions to model their impact. This modeling was hampered by uncertainty surrounding the quantity and distribution of plastics in the atmosphere.

"People have mostly taken measurements near the ground because they were thinking of these as a health hazard, which they are, but the climate is influenced by not just the amount at the surface but throughout the atmospheric column," Shindell said.

The analysis revealed that the warming effect from the microplastics and nanoplastics is about five times larger than their scattered cooling effect, establishing them as a previously unrecognized driver of global warming. And while the impact of microplastics on warming is tiny compared with the effect of burning fossil fuels, getting rid of plastic waste is another thing humanity could do to slow climate change, Shindell noted.

"It just adds another compelling reason why we should pay more attention to keeping plastic waste out of the environment," he said.