Are microplastics cooling and warming Earth’s climate?

This story was originally published by Cabling and appears here as part of the Climate Table collaboration.

Like ash thrown from a supervolcano, microplastics have infested the atmosphere and encircled the globe. These are pieces of plastic less than five millimeters long and come in two main varieties. The fragments are generated from bags and bottles that disintegrate (babies drink millions of tiny particles a day). in its formula), and microfibers are shed from synthetic clothing in washing and throw into the sea. The winds then sweep across the land and ocean, transporting microplastics into the atmosphere. The air is so lousy with things, that every year, the equivalent of more than 120 million plastic bottles they fall in 11 protected areas in the US, accounting for only six percent of the country’s total area.

In a new study published in the magazine NatureScientists have taken the first step in modeling how atmospheric particles might be influencing the weather, and it’s a strange mix of good news and bad news. The good news is that microplastics may be reflecting a small part of the sun’s energy back into space, which would actually cool the climate slightly. The bad news is that humanity is loading the environment with so much microplastic (ocean sediment samples show that concentrations have doubled every 15 years since the 1940s), and the particulates themselves are so varied, it’s hard to know how the pollutant will ultimately influence the climate. At some point they may 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, the model found. “They are very good at scattering sunlight back into space, so we see the cooling influence coming,” says atmospheric chemist Laura Revell, lead author of the new paper. “But they are also quite good at absorbing radiation emitted by the Earth, which means that they can contribute to the greenhouse effect in a very small way.”

Representation of the major sources of microplastics to the atmosphere and their relative contributions to deposition to the terrestrial environment over the western United States. Photo by PNAS

Like snowflakes, no two microplastics are the same – they are made from many different polymers, and they come in a rainbow of colors. The fragments break off as they fall through the environment, while the fibers break over and over again. And each particle grows a “plastisphere”From bacteria, viruses and algae.

So when Revell and his colleagues set out to build a model of how they affect climate, they knew it would be impossible to represent that much diversity. Instead, they determined the general optical properties of fibers and fragments as two main groups, for example, how well they would reflect or absorb the sun’s energy. 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 connected all of this to an existing climate model, which told them the estimated effect atmospheric microplastics would have on the climate.

The current net effect is basically a wash, they found. The slight cooling caused by the reflection would practically cancel out the slight heating caused by the absorption of the sun’s radiation. (They did not translate this into a possible temperature change for the overall climate.)

In reality, the Earth can get colder dust in the atmosphere. If you have heard of solar geoengineering, it is the same principle: airplanes spray aerosols, which bounce the sun’s energy back to space. Interestingly, cargo ships do too, albeit inadvertently: the pollution clouds they spew contribute to global warming and act as clouds reflecting light.

“However, I want to emphasize that this is not a good thing,” Revell says of the slight cooling effect. First, microplastic is its own danger to ecosystems, and our own bodies. And second, color is one of the limitations of such an early model. While the researchers based their model on unpigmented particles, microplastics come in a wide range of shades, particularly microfibers in clothing. 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 may discover that they are likely to lead to heating. At present, there is simply no way of knowing how many particles of what color are swirling in the atmosphere. In addition, microbes that grow on the particles can also change their reflectivity.

The weather station on the Waite campus of the University of Adelaide with equipment for measuring air pollution. Photo by denisbin / Flickr (CC BY-ND 2.0)

This new model is the beginning of the marriage of climate science and microplastics science. “This is an interesting first study on direct radiative forcing of atmospheric microplastics,” says Natalie Mahowald, an 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 and color of microplastics.”

As Mahowold points out, the distribution is another complicating factor for this initial model. Scientists can take air samples and characterize the microplastics that latch on, but these represent just a flash in a massive atmosphere; furthermore, the population of microplastics 100 feet above the ground could be very different than 1,000 feet. Smaller plastics, for example, could soar higher. Revell and his colleagues also used a set concentration, 100 particles per cubic meter of air, while the scientists get very different counts as they sample across the world. Above the ocean, the concentration of plastic may be less than one particle per cubic meter, but above Beijing they are 5,600and above london they are 2500.

Tiny bits of plastic swirl in the sky, and a new model suggests they could be subtly affecting the weather. #microplastics #Climate Change

And then there are the elder brotherPlastics, which are smaller than a millionth of a meter, break down larger bits until they finally reach the nano realm. Very few scientists have the equipment and expertise to sample nanoplastics, but one team working in the remote alps found that a minimum of 200 billion the particles fell in a single square meter of a mountain each week. The atmosphere is full of plastic particles, but scientists cannot detect all of them.

But there is an indication in the new model that the presence of so many pollutants is affecting the climate, and one area of ​​speculation is whether they are influencing cloud formation. A cloud forms when water slides over particles like dust. What if atmospheric microplastics actually act as additional nuclei?

In the laboratory, at least, scientists have observed the particles collect ice in special chambers that replicate atmospheric conditions. “This would be a really fascinating avenue if microplastics behaved in this way and contributed to clouds, just because clouds have such huge effects on the energy balance and the climate system,” says Revell. Larger, brighter clouds throw more radiation from the sun back into space, so this is one way that pollutants could divert energy.

Revell will be sampling more atmospheric microplastics to feed more data into its modeling. And it is very likely that over time there will just be more plastic to sample.

“Unless we really make big changes to the way we deal with microplastic pollution, and our plastic production rates and our waste management practices, then we just expect plastics to continue to fragment in the environment,” he says . Revell. “They will be producing plus microplastics. And those microplastics can be picked up by the winds and transported and have a great influence on the climate. “

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