A new study published in Nature Climate Change concluded that atmospheric microplastics may significantly contribute to global warming. The study showed that microplastics’ warming effect equates to about 16.2% of that of black carbon, or soot.
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In hotspots such as the North Pacific Subtropical Gyre, the warming effect of microplastics can exceed that of local black carbon by a factor of 4.7. The study indicates that the color and size of the particles determine their ability to absorb or reflect sunlight. Colored microplastics in black, yellow, blue and red exhibit light absorption coefficients 74.8 times higher than those of pristine or non-pigmented particles.
While white particles can have a slight cooling effect by reflecting sunlight, the warming effect of darker and colored particles significantly outweighs these potential cooling effects on a global scale.
The study also distinguished microplastics by size. Particles smaller than one micrometer, called nanoplastics, were found to be more potent warming agents. The researchers also found that the concentration of microplastics declines sharply with altitude, while nanoplastics maintain measurable concentrations even at 10 km, indicating longer atmospheric residence times and greater transport potential.
“This reveals a previously unrecognized climate pathway for plastic pollution. Plastic is not just a marine or health problem; it is also an atmospheric problem,” researcher Hongbo Fu said in an email to R&D World.
Previous studies only considered white particles
The researchers noticed that previous studies assumed microplastics were weak absorbers as they used only white or non-pigmented plastic parameters, Fu said in an email to R&D World.
Additionally, nanoplastics had been largely overlooked in climate contexts. It was this gap in the research that inspired the scientists to look into the optical properties of colored microplastics and nanoplastics and combine them with global transport modeling to estimate the true effect of microplastics on the environment.
Measuring optical properties
The researchers used a three-step framework. First, they measured the complex refractive index of individual colored particles using aberration-corrected TEM-EELS. Then, they calculated their mass absorption and extinction cross-sections using Mie Theory.
The second step was to simulate the global 3D distribution of microplastics and nanoplastics with an atmospheric transport model, FLEXPART. Finally, they fed the optical properties and concentrations into a radiative transfer model, SBDART, to compute direct radiative forcing.
Microplastics transform over time
Three-dimensional atmospheric transport simulations revealed a highly heterogeneous distribution of plastics across the globe. The research found that warming effects were most concentrated over specific pollution hubs and oceanic regions, including Mediterranean coastal regions, East Asia and eastern North America.
The study found that as the plastic particles drift through the atmosphere, they undergo photochemical ageing, which further complicates their climate impact. Exposure to UV and visible light causes white microplastics to yellow over time, increasing their absorption capabilities, transforming them from cooling to warming agents.
Conversely, some colored particles may bleach. However, the cooling effect of bleaching particles is offset by the yellowing of white particles.
The research found that even after ageing, microplastics maintain high radiative efficiency over their lifetimes. Long-term environmental exposure may promote the fragmentation of larger microplastics into nanoplastics, potentially increasing their overall warming effect.
Next steps: climate modeling, microplastic removal
Current climate assessments, such as those by the IPCC, do not account for the warming effect of microplastic particles. While the effect of microplastics is not an immediate emergency for global mean climate projections, it is a significant factor for regional assessments, Fu said in an email. Specifically for the atmosphere above the North Pacific Garbage Patch, the Mediterranean, East Asia and eastern North America, the omission of microplastic warming effects could be significant.
There are currently no viable technologies to remove microplastics from the open atmosphere. Reduction of plastic waste and reliance on fossil-fuel-derived plastic production is currently the only viable reduction strategy.
Plastic production itself contributes to approximately 3.8% of global CO2-equivalent emissions. Removing plastic from human systems could simultaneously reduce carbon emissions and atmospheric heating agents.
