Microplastics can cool and warm the Earth’s climate


Enlarge / Did you think climate change was already complicated? Now scientists must take into account the influence of tiny pieces of atmospheric plastic.

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Like ash spat out from a supervolcano, microplastics infested the atmosphere and circled the globe. They are pieces of plastic less than 5 millimeters long, and there are two main varieties. Fragments appear from disintegrating bags and bottles (babies drink millions of tiny particles a day in their formula), and microfibers come off synthetic clothing in the wash and evacuate to the sea. The winds then scour land and oceans, carrying microplastics high into the atmosphere. The air is so ugly with the stuff that every year the equivalent of more than 120 million plastic bottles fall on 11 protected areas in the United States, which represent only 6 percent of the total land area of ​​the country.

In a to study published today in the journal Nature, scientists set out to model how atmospheric particles might influence climate, and it’s a strange mix of good and bad news. The good news is that microplastics could reflect a tiny fraction of the Sun’s energy back into space, which would cool the climate slightly. The bad news is that humanity burdens the environment with so many microplastics (ocean sediment samples show that concentrations have doubled every 15 years since the 1940s), and the particles themselves are so varied, it is difficult to know how the pollutant will ultimately influence the climate. At some point they can end heating the planet.

The Earth absorbs some of the Sun’s energy while reflecting some of it, an exchange known as radiative forcing. Like other aerosols in the atmosphere, such as dust and ash, microplastics interact with this energy, according to the modeling. “They’re very good at bouncing sunlight back into space, so we’re seeing that cooling influence show up,” says atmospheric chemist Laura Revell, lead author of the new article. “But they’re also good enough at absorbing radiation emitted by Earth, which means they can contribute to the greenhouse effect in very small ways.”

Like snowflakes, no two microplastics are the same – they are made of many different polymers and come in a rainbow of colors. The fragments crumble as they fall into the environment, while the fibers separate again and again. And each particle develops a “plastisphere”Bacteria, viruses and algae.

So when Revell and his colleagues set out to build a model of how they affect the climate, they knew it would be impossible to represent so much diversity. Instead, they determined the general optical properties of fibers and fragments into two main groups, for example, how well they would reflect or absorb energy from the sun. They based their model on pure polymers without pigments and assumed an atmospheric composition of 100 particles per cubic meter of air. The researchers then plugged all of this into an existing climate model, which told them the estimated effect atmospheric microplastics would have on the climate.

Microplastic particles settled on a stainless steel membrane after filtration in the laboratory of the Institute for Environmental and Process Engineering at RheinMain University in Hessen, Rüsselsheim, Germany.
Enlarge / Microplastic particles settled on a stainless steel membrane after filtration in the laboratory of the Institute for Environmental and Process Engineering at RheinMain University in Hessen, Rüsselsheim, Germany.

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The current net effect is essentially a wash, they found. The slight cooling caused by the reflection would roughly cancel out the slight warming caused by the absorption of solar radiation. (They didn’t translate this into a potential temperature change for the global climate.)

The Earth could actually cool further because of dust in the air. If you’ve heard of solar geoengineering, it’s the same principle: planes spray aerosols, which bounce the energy of the Sun back in space. Oddly enough, freighters do it too, albeit inadvertently: the pollution clouds they spew both contribute to global warming and act as clouds reflecting light.

“I want to stress that this is not a good thing, however,” Revell says of the slight cooling effect. First of all, microplastics are its own danger to ecosystems – and our own bodies. And secondly, color is one of the limitations of such an old model. While the researchers based their model on unpigmented particles, microplastics come in a wide range of hues, especially wearable microfibers. Color will have a significant influence on potential radiative forcing: darker shades absorb more energy, while lighter colors reflect more. Once the colors of the particles are taken into account in future models, scientists can discover that they are in fact likely to lead to warming up. At present, there is simply no way of knowing how many particles of what color are swirling in the atmosphere. In addition, the microbes that grow on the particles can also change their reflectivity.

This new modeling marks the beginning of the marriage of climate science and microplastics science. “This is an interesting first study on the direct radiative forcing of atmospheric microplastics,” says Natalie Mahowald, atmospheric scientist at Cornell University, who has microplastics modeled in the atmosphere. “The results are likely to be very sensitive to assumptions about the size, distribution as well as color of microplastics.”

As Mahowold points out, the distribution is another complicating factor for this first model. Scientists can take air samples and characterize the microplastics they catch, but those are just one point in a massive atmosphere. Also, the population of microplastics at 100 feet above the ground could be very different from that at 1000 feet. Smaller plastics, for example, could swell higher. Revell and his colleagues also used a set concentration – 100 particles per cubic meter of air – as scientists get very different counts when they sample around the world. Over ocean, plastic concentration could be less than one particle per cubic meter, but above Beijing it’s 5 600, and above London it’s 2500.

And then there are the nanoplastics, which are smaller than a millionth of a meter, the product of larger pieces degrading until they finally reach the nano realm. Very few scientists have the equipment and expertise to sample nanoplastics, but a team working in the remote Alps found that at least 200 billion particles fell on a single square meter of mountain each week. The atmosphere is positively teeming with plastic particles, but scientists cannot detect them all.

But there is an indication in the new model that the presence of so many pollutants does something for the climate, and an area of ​​speculation is whether they influence cloud formation. A cloud forms when water settles on particles such as dust. What if atmospheric microplastics actually acted as additional nuclei?

In the lab, at least, scientists observed the particles collect ice in special chambers which reproduce atmospheric conditions. “It would be a really fascinating path then, if microplastics behave in this way and contribute to clouds, simply because clouds themselves have huge effects on the energy balance and on the climate system,” Revell explains. Bigger, brighter clouds send more of the solar radiation back into space, so it’s a way for pollutants to divert energy.

Revell will do more atmospheric microplastic sampling to feed more data into its modeling. And it is very likely that over time there will only be more plastic to sample. “Unless we really make huge changes to the way we deal with microplastic pollution, and our plastic production rates and waste management practices, we just expect plastics to continue. to fragment in the environment, ”Revell said. “They will produce Following microplastics. And these microplastics will be able to be picked up by winds and transported and have a great influence on the climate. “

This story originally appeared on wired.com.

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