Plastic Releases Greenhouse Gases When Exposed to Sunlight, Study Finds

Plastic is doing more than just polluting Earth’s soil and water—it’s polluting the air as well.

Researchers from the University of Hawaii at Manoa studied how plastic is affecting the environment beyond what scientists have already learned. According to research published in PLOS One on August 1, the scientists found that plastic can release methane and ethylene when exposed to sunlight.

Methane and ethylene are greenhouse gases, which can negatively affect the environment. Methane, for example, according to the Environmental Defense Fund, absorbs heat and warms the environment. It is released from natural sources as well as manmade sources, such as the oil and gas industries. The new research showed that it’s also coming from something else that’s abundant in the world.

It’s known that plastic releases many chemicals as it degrades, which can harm ecosystems and organisms. In this study, scientists tested what happens to common plastics when they were exposed to sunlight. They included polycarbonate, acrylic, polypropylene and high- and low-density polyethylene. Those plastics are used in many ways, including in textiles, construction materials and food storage. The scientists found the worst perpetrator of releasing those greenhouses gases to be polyethylene.

Polyethylene is used to create shopping bags and is the most produced and discarded synthetic polymer in the world. According to the Center for Biological Diversity, Americans use 100 billion plastic bags each year, and only 1 percent of those bags are returned for recycling. Every year, 100,000 marine animals are killed by plastic bags.

Scientists now realize they’re affecting much more than that. They learned that the emission rate of gases from the plastic only increased over time, including emissions from plastic in the ocean. The plastic emits the gases when exposed to sunlight, and continues to release the gases even when it’s dark outside.

"We attribute the increased emission of greenhouse gases with time from the virgin pellets to photodegradation of the plastic, as well as the formation of a surface layer marked with fractures, micro-cracks and pits," Sarah-Jeanne Royer, a postdoctoral scholar at University of Hawaii at Manoa and lead author of the study, said in a press release.

Plastic on Beach A beach in Málaga, Spain. Scientists found that polyethylene, which is used to create plastic bags, was the worst perpetrator of releasing greenhouses gases. JON NAZCA/REUTERS

Now the scientists plan to study the amount of plastic in the world that is exposed to the environment, specifically in oceanic and terrestrial regions. That will help them calculate the greenhouse gas emissions from plastics overall.

"Considering the amounts of plastic washing ashore on our coastlines, and the amount of plastic exposed to ambient conditions, our finding provides further evidence that we need to stop plastic production at the source, especially single-use plastic," Royer said.