When climate scientists first tried to estimate how airborne microplastics contributed to global warming, they modeled it as colorless, essentially transparent beads floating in the wind.
This is the simplest assumption and, for many years, the only one with sufficient data behind it.
Real plastic in the air is rarely transparent. It is stained, printed and weathered. And a new study found that these colored particles absorb about 75 times more sunlight than transparent particles.
That gap is large enough to draw plastics into a conversation that scientists are only just beginning to have.
How do microplastics become airborne?
Plastic doesn’t just end up in rivers or scattered on beaches. The pieces get airborne, travel thousands of miles on the wind, and settle somewhere on Earth.
Researchers have plucked it from the skies over remote mountains, glacial snow, and the open ocean. Previous research has shown that there are no more untouched places on Earth.
For many years, that fact was treated primarily as a pollution issue. The new study, led by Hongbo Hu, a professor of environmental science at Fudan University in Shanghai, treats this as a climate issue.
Floating plastic catches sunlight
Fu’s team started in the lab by measuring how real plastic particles absorb light. These measurements are input into atmospheric models that track where particles move around the world. They focused on microplastics, which are pieces smaller than a few millimeters, and nanoplastics, which are much smaller.
Clear plastic pieces fresh from the factory have little effect on sunlight. However, the dyed and colored parts that make up most real plastic absorb light about 75 times more strongly than the clear ones. This changes the image.
amazing heater
By absorbing light, the particles warm the surrounding air. Black carbon, the soot from the combustion of fuels and biomass, has long been on the climate register for this very reason.
Until this study, no one had quantified whether airborne plastics could play the same role on a global scale. According to Fu’s model, it could do so at a level equivalent to about 16 percent of the amount produced by black carbon.
That’s an absolutely modest amount. But the results are surprising for a substance that most people still imagine as a coastal pollutant, rather than as something that upsets the Earth’s energy balance from miles overhead.
Beyond the garbage field
Global averages underestimate local stories. At least according to models, the North Pacific’s subtropical gyre is a rotating eddy that traps garbage patches, and airborne plastic particles generate about 4.7 times more warming than black carbon in the same area.
Two things seem to be causing this gap. Marine debris releases plastic into the atmosphere through wave action and sea spray. And because the gyre is under relatively clear skies, there isn’t much soot around to interfere with the signal.
A previous paper published in 2021 estimated the warming impact of airborne plastic using assumptions about clean, colorless material.
New analysis suggests these numbers are too low because the world’s real plastic is dyed, printed, and weathered.
Aging of airborne microplastics
One might expect that the interaction between plastic and light would change depending on the sun and weather. They are possible, but in the opposite direction. White particles slowly turn yellow and absorb more light. The red ones are bleached and absorb less.
In the overall aerial mix, the two effects nearly cancel each other out. Modeling shows that plastic debris appears to continue to have a warming effect as long as it remains suspended in the air, regardless of age.
big unknown
How much plastic is actually there? This is up to an open question. Direct measurements exist in a few cities and a few remote locations, and the team’s model fills in estimates for the rest of the globe.
Greg Carmichael, Karl Kammermeyer Professor of Chemical and Biochemical Engineering at the University of Iowa and co-author of this paper, helped build much of the basic research on black carbon decades ago.
“They are important enough that we need to take them seriously and further quantify their role,” Carmichael said of airborne plastic debris. He added that observations globally are still too sparse to identify global concentrations with complete confidence.
Airborne microplastics and climate models
For the first time, microplastic pollution in the atmosphere has been given a number on the climate register. It’s not a small thing.
Its contribution to global warming is large enough to rank alongside soot and other recognized warming particles as a factor that scientists now need to consider.
Two results follow. Climate models can start treating plastic in the atmosphere as a warming factor, rather than ignoring it.
The push to reduce plastic production is usually discussed on health and ecological grounds, but now climate change is also being discussed.
Reducing the amount of plastic in circulation, especially dyed or colored plastic, also reduces the amount of plastic blown away by the wind. And this will help reduce global warming from causes that the world has only just begun to count.
This study nature climate change.
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