Microplastics, which are like supervolcano ash, have invaded the atmosphere and covered the planet. They are tiny pieces of plastic that measure less than 5 mm in length and come in two main types. Microfibers are able to break down synthetic clothing and flush it out into the sea. The microplastics are carried high by the winds that sweep land and sea. The atmosphere is so polluted that every year the equivalent of 120 million plastic bottles falls on 11 US protected areas, which only 6 percent of the country's total area.
Scientists have published a paper in Nature today that attempts to model how atmospheric particles might be influencing climate. It's a mixed bag of good and bad news. Good news is that microplastics could reflect a small amount of the sun's energy back into space, which could cool the climate slightly. Unfortunately, the bad news is that humans are putting so much microplastic into the environment (ocean sediment samples have shown that concentrations have been increasing by a factor of ten every 15 years since 1940s), and that the particles themselves can be so diverse that it is difficult to predict how this pollutant will affect the climate. They may eventually heat the planet.
Radiative forcing is a process whereby the Earth absorbs some sun's energy and also reflects some. The modeling showed that microplastics interact with the sun's energy in the same way as other aerosols like dust and ash. Laura Revell, an atmospheric chemist, is the lead author of this paper. They are also very good at absorbing radiation from the Earth. This means they can contribute to the greenhouse phenomenon in a small amount.
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Microplastics can be compared to snowflakes. They are made from many different polymers and come in a variety of colors. As they move around in the environment, fragments break down and fibers are broken up. Each particle is unique and each one grows its own plastisphere of bacteria viruses and algae.
Revell and her coworkers set out to create a model that would show how climate change affects them. However, it was impossible to capture so many variations. Instead they decided to determine the optical properties of fibers, and fragments, which were the main groups. This was how they would absorb or reflect the sun's energy. The researchers used pure polymers, without any pigments, to build their model. They assumed that 100 particles were present in each cubic meter. They then used this information to plug it into an existing climate model. This gave them an estimate of the impact that atmospheric microplastics could have on climate.
They found that the current net effect is basically an insignificant wash. The reflection effect would almost cancel out the warming from the sun's radiation. They didn't convert this into a possible temperature change for the entire climate.
Earth could actually receive more cooling from the dust in its atmosphere. Solar geoengineering is a similar concept to solar geoengineering. Planes emit aerosols that bounce the sun's energy into space. It is also possible for cargo ships to do this, though inadvertently. The clouds of pollution that they emit both contribute to global warming as well as act like light-reflecting clouds.
Revell says that the cooling effect is not good. Microplastic poses a danger to our bodies and ecosystems. Second, the early model is limited in color. Although the model was based on non-pigmented particles, microplastics can come in many colors, including clothing microfibers. Potential radiative forcing will be affected by color. Darker colors absorb more energy while lighter colors reflect more. Scientists may be able to determine if they will cause warming by incorporating the colors of these particles into future models. There is no way to know how many particles are swirling around in the atmosphere. The microbes that live on particles could also alter their reflectivity.
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This modeling represents the beginning of the marriage between climate science and microplastics science. Natalie Mahowald, Cornell University atmospheric scientist, has done research on direct radiative forcing of microplastics in the atmosphere. This is an intriguing first study. These results will likely be sensitive to assumptions about the distribution and size of microplastics as well as their color.
Distribution is another problem for this early model, Mahowold points. Scientists can collect air samples to characterize microplastics, but that is only one way of understanding the vast atmosphere. Plus, microplastics may be much more abundant at 100 feet than at 1,000 feet. Smaller plastics, for instance, might loft higher. Revell and her coworkers also used a concentration of 100 particles per cubic meter. However, scientists are finding wildly different counts from their sampling efforts around the globe. Plastic concentration may be lower than 1 particle per cubic meter over the ocean. However, it is higher in Beijing (5,600) and London (2,500).
Then there are nanoplastics. These are made up of smaller bits that are degrading into nanomaterials. Although few scientists have the expertise and equipment to sample for nanoplastics in their environment, one team from the remote Alps discovered that at least 200 billion particles were found on a square meter of a mountain every week. Although the atmosphere is positively overflowing with plastic particles, scientists are unable to detect them all.
The new model does show that there is evidence of climate change from the presence of pollutants. One area of speculation is whether these pollutants are influencing cloud formation. When water comes in contact with particulate matter such as dust, a cloud is formed. What if microplastics in the atmosphere are acting as additional nuclei instead?
Scientists have observed the particles collect ice in chambers that simulate atmospheric conditions. Revell says that this would be an interesting pathway if microplastics behaved in this way and contributed to clouds. This is because clouds have such huge impacts on the energy balance as well as the climate system. This is one way in which the pollutants could divert energy.
Revell will continue to sample more atmospheric microplastics in order to provide more data for her modeling. It's likely that there will be more plastic to sample over time. Revell says that unless we make significant changes in how we deal with microplastic pollution and our rates at plastic production, as well as our waste management practices and policies, we can expect plastics to continue to break down in the environment. They will be making more microplastics. These microplastics can be carried by the wind and influenced the climate.
This story first appeared on wired.com
