Scientists have long been concerned about microplastics contaminating the food we eat, the water we drink and the air we breathe. Now, new research has uncovered a previously unknown threat: tiny pieces of airborne plastic are actively contributing to global warming.
An international research team, reporting in Nature Climate Change, has found that coloured microplastics in the atmosphere trap heat by absorbing light, thereby warming the air around them. Plastic debris becomes airborne when larger items break down into minuscule bits that are then swept up by wind and sea spray.
The study was led by Professor Drew Shindell, Nicholas Distinguished Professor of Earth Science at Duke University’s Nicholas School of the Environment, in collaboration with researchers at Fudan University in China. The team used computer simulations and laboratory experiments to analyse how light and heat interact with tiny particles of plastic.
They discovered that these particles come in a variety of colours that intensify as the plastic ages, and those hues give the debris significant warming power. Pigmented microplastics absorb roughly 16% as much heat as black carbon, one of the planet’s most potent warming agents.
To put this in perspective, Shindell said that microplastics in the atmosphere have approximately the same warming effect as running 200 coal-fired power plants annually.
The research expands the known family of aerosols to include microplastics. Previously, old climate models had assumed airborne microplastics to be colourless, meaning they were considered negligible contributors to warming. In fact, colourless atmospheric aerosols, such as water droplets in clouds, actually cool the planet by reflecting sunlight away from Earth. Shindell’s research tells a very different story.
The researchers also used their data to predict where these airborne microplastics exist globally. Unlike black carbon, which concentrates largely over land, airborne microplastics congregate over the North Pacific Subtropical Gyre, the massive system of ocean currents spanning nearly eight million square miles that collects vast amounts of plastic debris. When waves break over this detritus, sea spray launches microplastics into the air, making the gyre a significant source of atmospheric microplastics.
Currently, microplastics do not appear to be a major climate threat, according to Shindell. However, he hopes his study – which focused on airborne microplastics closest to the Earth’s surface – will inspire other teams to measure microplastics throughout the lower atmosphere for a more complete picture of their effects on warming.
The urgency of the issue is clear. Plastic pollution is projected to surge over the next decade. Without significant action to reduce plastic use and waste and improve recycling, plastic leakage into the environment could increase by 50 per cent from 2020 levels, reaching 30 million tons by 2040, according to the Organisation for Economic Co-operation and Development.
Shindell said: ‘Targeting microplastics is not going to solve our climate problem by any means, but removing the equivalent of 200 coal-fired power plants would be a nice contribution to getting our [carbon dioxide] down.
‘We have so much work to do to get down to something like a Paris Agreement. We really need every single thing at our disposal.’
The full research can be read here
Photo: Rui Stenio