Like ashes ejected by a supervolcano, microplastics have invaded the atmosphere and surrounded the globe. These are pieces of plastic with a length of less than 5 millimeters and are available in two main varieties. Fragments multiply from crumbling bags and bottles (babies drink millions of small particles a day in their formula), and microfiber is detached from synthetic clothing when washed and poured into the sea. The winds then travel around the land and ocean, carrying microplastics high into the atmosphere. The air is so bad that every year the equivalent of more than 120 million plastic bottles falls on 11 protected areas in the United States, which make up only 6 percent of the country’s total area.
In a study published today in the journal Nature, scientists have made the first move in modeling how atmospheric particles can affect the climate, and this is a strange combination of good and bad news. The good news is that microplastics can reflect a small amount of solar energy back into space, which would actually cool the climate so slightly. The bad news is that humanity is charging the environment with so much microplastic (ocean sediment samples show that concentrations are doubling every 15 years since the 1940s), and the particles themselves are so diverse that it’s hard to understand how the pollutant will eventually affect the climate. At some point, they may end heating the planet.
The earth absorbs part of the sun’s energy while reflecting part of it, an exchange known as radiation coercion. 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 that the cooling effect comes through them,” said atmospheric chemist Laura Revel, lead author of the new report. “But they are also quite good at absorbing radiation emitted by the Earth, which means they can contribute to the greenhouse effect in a very small way.”
Like snowflakes, no two microplastics are the same – they are made of many different polymers and come in rainbow colors. The fragments are crushed as they move around the environment, while the fibers are separated again and again. And each particle grows a unique “plastisphere” of bacteria, viruses and algae.
So when Revel and her colleagues set out to create a model of how they affect the climate, they knew it would be impossible to present so much diversity. Instead, they determined common optical properties of fibers and fragments as two main groups – for example, how well they would reflect or absorb solar energy. They base their model on pure pigment-free polymers and adopt an atmospheric composition of 100 particles per cubic meter of air. The researchers then incorporated all of this into an existing climate model, which told them the approximate effect that atmospheric microplastics would have on the climate.