Plastic waste in the sea causes greenhouse gases

For some time now, reports and debates have been piling up about the extent to which plastic poses a health risk to humans and the long-term damage associated with plastic waste that ends up in the environment. While it is well known that plastic particles accumulate in the stomachs of fish, marine mammals and birds. The islands of plastic trash floating around in the oceans are also, unfortunately, nothing new. But now a group of researchers at the University of Hawaii has discovered, rather by accident, that plastic releases greenhouse gases during its decomposition process.

Originally, the researchers had wanted to find out how much methane escapes from seawater. However, they found much higher levels than they had suspected. In their opinion, these high levels of methane could not have come from marine animals alone. The answer lay in the plastic bottles in which the water samples were stored. This incidental discovery showed the researchers that plastic also emits methane.

The smaller, the higher the emissions

Her colleagues' findings piqued Sarah-Jeanne Royer's interest and she began her own research into the new discovery. The Canadian oceanographer and her research team studied the seven most common types of plastic. To do this, they placed plastic samples in quartz tubes and placed them in the tropical sun. Again, the plastic was found to produce the greenhouse gases methane and ethylene. And what's more, polyethylene emits the largest amount of gases of all types. This is the material that is mainly used for many disposable products and plastic bags.

Royer explains that polyethylene is a flexible material consisting of simple hydrocarbon molecule chains. Due to its weak chemical structure, it therefore emits a lot of greenhouse gas as soon as it decomposes in the sun.
In further investigations, Royer and her colleagues found that methane emission increases the smaller the plastic particles are. Very fine powder therefore produces almost 500 times more methane than the same amount of plastic in the form of larger particles. This discovery is particularly worrying because plastic is breaking down into smaller and smaller components due to solar radiation all over the world and is therefore also likely to emit more and more methane.

When asked about the strength of the impact of these greenhouse gases emitted by plastic on global warming, Royer points out that more research needs to be done. More information needs to be gathered in order to make clear statements.

Emission quantity comparatively low

Compared to the amounts of methane emitted by other sources, the emission from plastic appears to be rather small. Royer and her colleagues note in their research paper that it is likely to be a thousand times smaller than the amount of greenhouse gases emitted into the environment by coal and gas production, factory farming and landfills. However, the situation is different for ethylene and other gases. These could have a greater impact on global warming.

Plastic is therefore not only a danger to the oceans and their inhabitants, but also shows previously unexpected chemical reactions. Climate researcher Gunnar Luderer is taking this as an opportunity to look into the topic more closely than before. He and his colleagues at the Potsdam Institute for Climate Impact Research are studying the global carbon cycle. Since around 5 billion tons of plastic have been released into the environment by humans to date and this material is involved in the creation of greenhouse gases, plastic is also becoming increasingly relevant in Luderer's field of research. After all, it doesn't stop at this amount, as hundreds of millions of tons of plastic are estimated to be added each year. According to Luderer, it is particularly important to advance research in the field. Laboratory experiments do provide useful insights. But field research can better understand what exactly happens to the plastic that ends up in the environment, he said. The effects and consequences on nature are made directly observable in the real world with the help of this research method.

Plastic is everywhere

Since plastic is now found in an infinite number of products and accumulates not only in the sea but everywhere in the environment, Sarah-Jeanne Royer is now also directing her research to the mainland. Because the methane does not only flow out of the plastic that is in the water. Using her plastic samples, Royer was able to determine that polyethylene releases even more of this greenhouse gas in the air. In fact, twice as much as in the water. The oceanographer reports with unease that all the plastics that surround us in everyday life are continuously emitting methane. She is referring not only to the plastic waste that ends up in landfills, but also to greenhouses, cell phones and cars.

At present, there is not enough data on this topic to draw a global picture of the impact of greenhouse gases from plastic. Nevertheless, the emission of methane, ethylene and other gases during plastic decomposition processes is a field of research that is gaining importance for good reason.