This led us to think of a plastic cycle: microplastics do not stay in soils, rivers, the ocean or the air, but move between different parts of the earth system.
Initially, we expected airborne microplastics to diffuse sunlight like most aerosols, which act like tiny disco balls and reflect sunlight back into space. This has a cooling effect on the Earth’s climate.
Most types of aerosols in the Earth’s atmosphere scatter light – therefore, in general, aerosols have partially offset the warming of greenhouse gases in recent decades. An exception is soot (or carbon black), which absorbs sunlight well and has a warming effect.
We have found that, overall, airborne microplastics are effective in diffusing sunlight, which implies a cooling effect on the climate. However, they can also absorb radiation emitted by the Earth, which means that they contribute very little to the greenhouse effect.
Impacts of microplastics on the climate
The highest reported concentrations of airborne microplastics (thousands of fragments per cubic meter of air) were measured at urban sampling sites in London and Beijing.
We don’t yet know how far the microplastics reached the atmosphere, but an aircraft study found them at elevations of up to 3.5 kilometers.
This poses additional questions as to whether microplastics could alter atmospheric chemistry by providing surfaces on which chemical reactions occur and how they interact with clouds.
The magnitude of the influence of microplastics on climate varies in our climate model simulations, depending on the assumptions we made about how plastic fragments are distributed in Earth’s atmosphere.
Because airborne microplastics research is so new, we have had a limited number of studies to inform our research.
Our study shows that the influence of microplastics on the global climate is currently very weak, and that a cooling effect dominates. However, we expect it to increase in the future, to the point that airborne microplastics exert a climatic influence comparable to other types of aerosols.
It is estimated that 5 billion tonnes of plastic waste has already accumulated in landfills or in the environment to date. This figure is expected to double over the next three decades. Without serious efforts to tackle microplastic pollution, poorly managed plastic waste will continue to increase the abundance of airborne microplastics and their influence on climate in the future.
This article is republished from The Conversation under a Creative Commons license. Read the original article here.