Plastic dispersed in the environment releases greenhouse gases during the decomposition process. According to new research, plastic pollution thus contributes to climate change.
Plastic waste dispersed in the environment and in water contributes to the greenhouse effect and therefore to global warming. The discovery comes from a group of researchers who conducted numerous tests near the Hawaiian islands. The results, published in the scientific journal PlosOne, are alarming: as this material degrades, it emits in particular two greenhouse gases, ethylene and methane. The latter is particularly potent: although it persists less in the atmosphere than carbon dioxide, during the period in which it is active it is capable of producing warming 25 times greater than that generated by CO2.
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Plastic has not yet been recognised as a source of greenhouse gases contributing to climate change. Yet the presence of these gases will increase as plastic accumulates in the environment, because the decomposition process of the material, caused by environmental factors such as light, heat, moisture, chemical oxidation and biological activity, leads to physical and chemical changes in its structure.
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Plastic does not degrade only when it is thrown into water. In fact, the situation is worse when solar irradiation occurs in a dry environment: ethylene production is 76 times greater than in an aquatic environment. Researchers Sarah-Jeanne Royer, Sara Ferrón and Samuel T. Wilson of the University of Hawaii observed the degradation of the most common plastics (polycarbonates, acrylics, polypropylene, polyethylene) over a period of approximately seven months, concluding that the most prolific polymer in terms of greenhouse gas production — in particular those mentioned above — is polyethylene, already known for releasing additives into the environment, again as a result of the decomposition process.
This is the most widely used synthetic polymer of all: it accounts for 36 per cent of all plastic produced in the world. From packaging to containers, from the inner lining of packages to toys, from pipes to caps, polyethylene is used in a myriad of mass-market products and is consequently also the most widespread plastic waste in the environment.
Furthermore, the degradation of plastic in the environment leads to the formation of smaller units, microplastics, thereby multiplying the surface area of the material exposed to the elements that contribute to its decomposition, and thus accelerating the production of greenhouse gases. Given the rate at which plastic is produced and used, the fact that only 15 per cent of it is recycled globally and that more than 12 million tonnes end up in the sea every year, methane and ethylene emissions risk continuing to rise, posing serious problems in terms of climate.
Since the effects are caused not only by plastic in the seas but also by that on land, "the calculation must also include all the waste dispersed on land, in cities, in landfills, in construction materials and even from clothing," the research states. "Due to the longevity of this material and the large amount of plastic that persists in the environment, questions regarding its contribution to global methane and ethylene levels should be prioritised and taken into consideration by the scientific community," the study's conclusions read. For Royer, co-author of the research, there is only one solution, namely to stop the production of plastic, especially single-use plastic, at the source.