Airborne microplastic particles could start having a significant effect on the world's climate in the future, a new paper reports.
New research at the University of Canterbury, New Zealand, found that airborne microplastics reflect part of the sunlight incoming to the Earth's surface, thus cooling down the climate. For now, this effect is extremely slight. However, as the quantity of microplastics in the air is bound to increase in the coming decades, this effect will grow in magnitude.
"Yes, we focussed on airborne microplastics," Dr. Laura Revell, Senior Lecturer of Environmental Physics at the University of Canterbury and the paper's corresponding author told ZME Science in an email. "These were first reported in Paris in 2015 and have since been reported in a range of urban and remote regions."
"However, we believe that microplastics may be co-emitted from the ocean with sea spray, leading to the concept of the ‘plastic cycle’ i.e., microplastics might be carried with the winds over some distance, be deposited to land, get washed into a river, be transported into the ocean, and then re-enter the atmosphere."
Microplastics are a growing environmental concern. They're already present in soils, water, air, and their levels are steadily increasing. Some microplastics are produced directly, for items such as cosmetics, while others are the result of plastic items breaking down in landfills.
Due to their small size and weight, such particles can easily be picked up by winds and carried over immense distances. Large cities such as London or Beijing show huge concentrations of such particles, likely due to how much plastic is used within their boundaries.
That being said, we're just beginning to understand their full impact as airborne contaminants. The present study helps further our understanding in this regard, by uncovering the interaction between these particles and the planet's climate. According to the authors, this is the first time the direct effects of airborne microplastics on climate has been calculated.
Other airborne solutions ('aerosols') are known to have an effect on the Earth's climate either by scattering or reflecting incoming sunlight back into space, cooling everything down, or by absorbing radiation on certain frequencies, which warms the planet up.
Against that backdrop, the authors set out to determine what effect airborne microplastics have in this regard. They used climate modeling software to determine the radiative effect (i.e., reflective of absorbing) of common airborne microplastic particles. They focused primarily on the lower layers of the atmosphere, where much of the microplastic contamination is located. Overall, they report, these particles scatter solar radiation, which amounts to them having a minor cooling effect on the climate at surface level.
Exactly how much cooling they produce, however, the team can't say for sure. We simply don't have enough measurements of the quantity and distribution of microplastics in the atmosphere, nor do we have solid data on their chemical composition and physical properties.
Further muddying the issue is that microplastic particles can also have a warming effect, which may partially or completely counteract the cooling they cause through the scattering of light.
"After we calculated the optical properties of microplastics to understand how they absorb and scatter light, we realised that we would see them absorbing infrared radiation and contributing to the greenhouse effect. That moment was a surprise, as up until then we had been thinking about microplastics as efficient scatterers of solar radiation," Dr. Revell adds for ZME Science.
This absorption takes place on a frequency interval of infrared light where greenhouse gasses such as CO2 don't really capture much energy. In other words, these microplastics tap into energy that's not readily captured by the current drivers of climate warming.
"Microplastics may therefore contribute to greenhouse warming, although in a very small way (since they have such a small abundance in the atmosphere at present)," Dr. Revell adds. "The dominant effect we see in our calculations with respect to interaction with light, [however] is that microplastics scatter solar radiation (leading to a minor cooling influence)."
In closing, she told me that more recent studies on the topic of airborne microplastics are reporting "quite high" concentrations of these particles in certain areas of the world, such as Beijing. Dr. Revell explains that this is likely due to improvements in technology allowing researchers to pick up on particles of much smaller diameters than before -- which passed by undetected before. All of this uncertainty in the data obviously does not bode well for our conclusions.
"Our initial estimates of the climate effects of airborne microplastics are just that -- estimates -- and will no doubt be revised in future as new studies are performed and gaps in our knowledge are filled," Dr. Revell concluded for ZME Science.
However, one thing we do know for sure is that with plastic pollution on the rise, the effects of microplastics on the climate are only going to become worse. It's very likely that it already shapes atmospheric heating or cooling on the local level, the authors explain. If steps are not taken to limit the mismanagement of plastic waste, this effect will grow in magnitude and keep influencing the climate for a long period in the future.
The paper "Direct radiative effects of airborne microplastics" has been published in the journal Nature.