How plastic waste accelerates climate change
Sarah-Jeanne Royer is an oceanographer and post-doctoral researcher at Scripps Institution of Oceanography. She specializes in plastic and microfibre degradation in the environment. When working with researchers at the University of Hawaii in 2015 they discovered that plastic debris in the ocean is a considerable source of methane and other greenhouse gas emissions. In her research she works towards a better understanding of this process but also towards convincing leaders and policy makers to develop better laws to reduce the production and consumption of plastic.
Joel: We’ve all seen horrible images of plastic pollution in oceans and on shores. Especially in South Asia, where the capacity for waste management is limited, we face a growing plastic problem in the coming years. Now, on top of that, your team discovered that plastic waste also emits greenhouse gases. Can you tell me more about that?
Sarah-Jeanne: Yes, this was actually an unexpected discovery. My colleagues set out to measure methane gas production from biological activity in the ocean. While they were collecting and incubating sea water, they measured methane concentrations which were much higher than expected. They realized that the methane emissions were coming from the plastic bottles in which they were incubating sea water. The bottles were a much bigger source of the gas than the biology itself. I found this very interesting and decided to concentrate my research in this area.
Joel: Wow, that’s insane. What causes the plastic to emit these gases?
Sarah-Jeanne: So, the plastic emits methane and other types of greenhouse gases such as ethylene, ethane and propylene as it photodegrades. These hydrocarbons get synthetized during the reorganization of the chemical molecules mostly due to the effect of oxidation. These gases are only a small fraction of what get emitted from plastics. However, we could not measure all the variety of gases produced due to instrumental limitations. We also measured carbon dioxide and carbon monoxide. Most of the gases we measured have a negative effect on the environment and an effect on climate change. We tested this for the seven most commonly used types of plastics and found that LDPE, which stands for low density polyethylene, emits most gases. Unfortunately, this is also the most commonly produced and discarded type of plastic into the environment.
Joel: You’re talking about plastic bags, candy wrappers — the so called multi-layer packaging — and other types of single-use plastics.
Sarah-Jeanne: Exactly. I decided to focus on LDPE only and then made another alarming discovery: When plastic degrades the surface area increases and more and more gases are being released. Once exposed to UV light the off-gassing never stops. We compared LDPE-powder to LDPE-pellets and found that the powder produced 488 times more methane than the pellets. This means that as the plastic degrades and fragments in the environment the production of greenhouse gases can only increase. This is bad news.
Joel: Does this only happen when sunlight and water are involved? What about the plastic waste on land and in landfills?
Sarah-Jeanne: As an oceanographer, obviously I’m interested in looking at plastics submerged in water. But we decided to lead an experiment where we compared our initial research to plastic exposed in air and on land. We discovered that plastic in air produces three times more methane and 76 times more ethylene and other greenhouse gases than when submerged in the water.
Joel: So, what does this mean?
Sarah-Jeanne: When we talk about plastic pollution as a global issue, we often refer to the ocean. But in terms of greenhouse gas emissions, it is actually also a huge problem for terrestrial environments. Think about all the types of plastic you find in the street, in your backyard, in the swimming pool, as well as in landfills: All of them continuously emit greenhouse gases once they have been hit by UV light. And they continue to emit gases, even if you would take that plastic into your house or store it in the dark.
Joel: That’s shocking. I am wondering: You only really hear about methane emissions when it comes to biological waste in landfills. How bad are emissions from a piece of plastic compared to, for example, a rotting apple?
Sarah-Jeanne: Good question. We tried to find estimates for all the plastic floating at the surface of the ocean and compare its greenhouse gas production to that of biological waste on land. We found that their emissions were quite similar. But then, we don’t have accurate numbers about the quantity of plastic currently exposed to air as we mostly look at the ocean.
Joel: Let’s talk solutions. As we know, only 9 per cent of plastic worldwide actually gets recycled. The rest is either incinerated or ends up in landfills or in the ocean and now, thanks to your research, we know that these become hotspots for greenhouse emissions. How do we solve this dilemma?
Sarah-Jeanne: Well, of course, we all know, the best solution would be to stop using plastic altogether but of course, for now, this is unrealistic. I feel strongly about reusing plastic, but we have to be smart about it. For instance, the textile industry is turning PET plastic bottles into polyester but when we wash these clothes synthetic microfibers will go back into the environment. Then there are projects in the field of construction which “hide” big chunks of plastic in housing structures and in road construction. These solutions are not perfect yet and still at a small scale but they are better.
Joel: These projects sound interesting but if you look at the global plastic production volume and the amounts of plastic waste already out there, I doubt that they will solve the problem.
Sarah-Jeanne: Of course, there is the option of burning plastic but then we wouldn’t repurpose it, we would end its lifetime.
Joel: I think we all agree that incineration can only be a bridge technology to handle the plastic which cannot be recycled. Yet burning it will at least reduce the greenhouse gas emissions of plastic because if we burn something, the mentioned gasses won’t be released. So, this is actually what we do. We incinerate plastic waste as a replacement to coal and gas in cement production. We really see no better option at the moment. What do you think?
Sarah-Jeanne: I think it’s going to be more expensive, but it is better than landfilling it openly. We have to pay the price otherwise the planet will suffer. I think there are many different ideas and projects and yours is one of them. I would love to hear back from how it is going.
Joel: And I cross my fingers for future findings in your studies, too. Thank you for this interesting conversation.
About Cleanhub: Cleanhub is a company dedicated to free the planet from plastic pollution, while offering solutions for brands to have verifiable environmental impact. Cleanhub works in global partnerships to recover plastic waste from the natural environment, while its traceability technology keeps account of the person, quantity, quality and location of all activities.
