Airborne microplastics affect climate change

Microplastics in the atmosphere are likely to directly affect climate change in the decades ahead, according to a new study.

The modelling work by University of Canterbury and Te Herenga Waka—Victoria University of Wellington researchers is the first to investigate the effects of airborne microplastics on climate.

The research—led by Canterbury’s Dr Laura Revell and her colleagues Dr Peter Kuma and Professor Sally Gaw, and MacDiarmid Institute for Advanced Materials and Nanotechnology researchers Professor Eric Le Ru and Dr Walter Somerville at Te Herenga Waka—has been published in the scientific journal Nature today.

Microplastics are tiny fragments or fibres resulting from the breakdown of larger plastics. They are blown across the Earth and are measurable above some of the world’s largest cities.

Because they can absorb, emit and scatter radiation, like dust and greenhouse gases, they can affect the climate by cooling or warming the atmosphere.

Professor Le Ru, from Te Wānanga Matū—School of Chemical and Physical Sciences, says the impact of these microplastics on climate, “at the median concentration measured to date”, is still negligible.

“We’d need 100-times greater concentrations to see a significant effect. But the main result was that we understood at what concentrations we should start to take this into account with respect to the climate.”

A median concentration about 100 times that of today’s is already found close to megacities, he says.

“Lots of these microplastics end up in the oceans and waterways, and wildlife unknowingly eat them, but some are also found in the atmosphere.

“The smaller they are, the further they can be blown up in the atmosphere by winds. The size varies a great deal, from 10s to 100s of nanometres in size to more than 1mm. The shapes are also diverse, from spheres to very long fibres.

“One thing that hadn’t been looked at was how these might affect climate. Any particle suspended in the atmosphere will have an effect on the climate—either by absorbing energy emitted from the Earth, causing warming, or by reflecting light from the Sun, leading to cooling,” Professor Le Ru says.

He and MacDiarmid-funded Postdoctoral Fellow Dr Somerville calculated the optical properties of these particles, from ultraviolet to infrared wavelengths.

“It was tricky work because of such a wide range of sizes and shapes. We had to develop tools to approximate them, and our colleagues at Canterbury used our results as parameters in global climate models to see if there was any effect on temperature and climate.

“More work needs to be done to improve our models and see how microplastics’ reflectivity and absorption of sunlight may cancel each other out, or not,” he says.

For the study, Prof Le Ru and Dr Somerville modified and combined techniques already used to investigate the optical properties of metallic nanoparticles.

“Even supercomputers struggle to calculate the contribution to climate change, given particles’ different  shapes, different orientations and different sizes.

“It was a mixture of computer work—and implementing theories on computer—along with good old-fashioned pen and paper calculations and mathematical physics to speed up the calculations.

“The climate model calculations were carried out on the national supercomputer at Canterbury and the optical properties were computed on the University’s high-performance computing cluster Rāpoi.”

Dr Revell says it is important to know if airborne microplastics may become a bigger issue in future.

About five billion tonnes of plastic waste is now in landfills or the environment, an amount expected to double in the next 30 year if current trends continue.

“Since plastic degrades through age and exposure to light to produce microplastics, we expect microplastics to be present in Earth’s atmosphere for many years to come,” Dr Revell says.

“Indeed, if the global average concentration increases to values already seen in some megacities, then the effect of airborne microplastics on climate will be significant and potentially similar in size to other atmospheric aerosols routinely included in climate models.”

The joint research was supported by a three-year-long $300,000 Marsden Fund Fast-Start grant.