Plastic aerosols in the atmosphere could affect the climate

Tiny particles of plastic in the atmosphere can affect Earth’s climate, according to Laura Revell at the University of Canterbury in New Zealand and colleagues. New calculations of the heating and cooling effects of airborne microplastics reveal that the overall influence on climate is strongly dependent on the distribution of microplastics in the atmosphere – which is currently poorly understood.

Today, roughly 5 billion tonnes of plastic waste have accumulated in landfills and natural environments. As the material breaks down over time, it releases vast quantities of microscopic particles – which due to their small size and low density, can be transported across the globe by winds and ocean currents. Although the threats these microplastics pose to natural ecosystems are now being studied extensively, their influence on Earth’s climate is still virtually unknown.

Climate scientists know that aerosols like dust, pollen, and soot will alter temperatures on Earth’s surface as they scatter and absorb sunlight. As a result, the effects of these particles are quantified in climate models that predict future changes in global temperatures. Yet even as airborne microplastics become an ever-larger part of the mix of atmospheric aerosols, their radiative influence is still virtually unknown.

Altitude matters

In their study, Revell’s team present the first detailed calculations of the optical properties and radiative effects of airborne microplastics. Assuming that microplastics are present in atmosphere up to altitudes of 10 km, the team’s models predicted a small positive effective radiative forcing. This means that the particles reflect slightly less solar energy back into space than they absorb, which has a slight warming effect on the surface of the Earth.

However, exactly how microplastics are distributed in the atmosphere is not well known. If instead, the particles are entirely confined to the 2 km layer of the atmosphere lying directly above the Earth’s  surface, Revell and colleagues calculate a larger negative effective radiative forcing – and therefore a small cooling effect. This effect, however, is much smaller than that known to be caused by other types of aerosols in the atmosphere.

Regardless of which prediction is more accurate, the researchers found that the influence of microplastics on Earth’s surface temperature is currently far weaker than other types of atmospheric aerosol.

Amounts of plastic waste accumulated in landfill and natural environments has risen rapidly over the past 70 years. It is expected to double over the next 30 years unless significant, global-scale action is taken. As climatologists learn more about how microplastic pollution is being distributed throughout the lower atmosphere, the team’s results will allow for more accurate predictions of how microplastic aerosols could affect the climate.

The research is described in Nature.

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