Microplastics are abundant in the world’s waterways and even in the air. In fact, researchers estimate there are hundreds to thousands of microplastic particles in each cubic meter of air in urban environments.
University of Canterbury environmental physicist Laura Revell wondered how atmospheric microplastics might impact the climate. After all, she says, “other types of particulates in the atmosphere, such as dust, soot, and sulfate aerosols, influence the climate by absorbing and scattering sunlight.”
To determine whether atmospheric microplastics are warming or cooling the planet, Revell’s group analyzed their optical properties, finding that the types of particles assumed to be abundant scatter ultraviolet and visible light but absorb infrared radiation. The researchers plugged those data, along with estimates of these particles’ abundance, into a global climate simulation (Nature 2021, DOI: 10.1038/s41586-021-03864-x).
The climate impact of microplastics depends on what altitudes they reach—something researchers don’t yet know, Revell says. If microplastics stay close to the planet’s surface, her team estimates that they have a small cooling effect of about 0.75 mW/m2. If they travel as far as about 10 km from Earth’s surface, microplastics are likely contributing to global warming, adding 0.045 mW/m2 or more. These numbers are small compared with those of greenhouse gases but are significant, Revell says. She adds that more research is needed to determine the climate impacts of atmospheric microplastics, especially since plastic pollution is projected to grow in coming decades.