Tiny pieces of plastic in the air may have a minor cooling effect on our climate by reflecting sunlight.
In recent years, microplastics floating in the atmosphere have been detected around the world, with the highest concentrations found in the air above London and Beijing. With a size of between 15 and 250 micrometres, similar to the thickness of a strand of hair, airborne microplastics are bigger than most other aerosols in the atmosphere, such as black carbon and sulphates. However, due to their low density, microplastics particulates are easily carried over large distances.
These extremely small pieces of plastic typically come from synthetic textiles, such as polyester, synthetic rubber tyres, paint and even bits of larger plastic that have been broken down by the environment.
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at the University of Canterbury in New Zealand and her colleagues investigated the effect these airborne microplastics have on our climate. After calculating the optical properties of microplastic pieces, the team used a global climate model to evaluate their overall effect. The modelling assumed a microplastic concentration of 100 microplastic particles per cubic metre of air, in line with the average concentrations reported in previous studies.
Microplastic particles both reflect sunlight back out to space and absorb heat emanating from Earth鈥檚 surface, which means they contribute to climate cooling and warming respectively. However, the researchers discovered that microplastics have an overall cooling effect on the climate, as they reflect more heat than they absorb.
But the team also found that this cooling effect is negligible compared with the cooling and warming influences of greenhouse gases and other atmospheric aerosols. The atmospheric concentration of microplastic particles is several orders of magnitude smaller than other types of atmospheric aerosols, which is why their climate effect is so small, says Revell.
鈥淗owever, given that microplastic pollution is increasing, we do expect microplastic abundance to grow in the future,鈥� she says. 鈥淎nd their impacts may increase to the point where microplastics have a climate effect that is similar to other types of atmospheric aerosols.鈥�
Despite their minor contribution to global cooling, microplastics shouldn鈥檛 be viewed positively, says Revell. 鈥淲e know that microplastics are harmful when inhaled, so we actually don鈥檛 want [them] floating in our air; they鈥檙e also damaging to wildlife and ecosystems.鈥�
鈥淭his is a good cautionary tale that even if the world were to successfully tackle the greenhouse problem, we still need to think carefully about how everything else we do could be changing the climate,鈥� says at the University of Leeds in the UK.
Nature
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