We've been hearing for years now about the negative effects of plastics. Some types of plastic leach endocrine-disrupting chemicals into food, while others choke or fill the bellies of marine animals until they die a torturous death. There are the now-infamous gyres of collected plastics swirling around our oceans, and microplastics have worked their way into shellfish, sea salt and even bottled water. Yes, we're all definitely eating plastic.

Now, a postdoc, Dr. Sarah-Jeanne Royer at the University of Hawai'i at Mānoa School of Ocean and Earth Science and Technology (SOEST), has discovered that plastics are also releasing methane and ethylene — greenhouse gases directly linked to global warming. Shockingly, our plastic dependence — in many cases for convenience products — is not only cluttering up beaches with ugly pollution and asphyxiating sea turtles, it's contributing to a warming world.

Royer stumbled across the phenomenon when she was testing to see how much methane came from the normal biological activity in sea water. She realized during testing that the plastic bottles that she put the water samples in were generating more methane than the organisms in the water. It was an unexpected discovery, but scientists follow where the evidence takes them, so Royer pursued the idea.

"The science team tested polycarbonate, acrylic, polypropylene, polyethylene terephthalate, polystyrene, high-density polyethylene and low-density polyethylene (LDPE) — materials used to make food storage, textiles, construction materials, and various plastic goods," detailed a release from SOEST.

"Polyethylene, used in shopping bags, is the most produced and discarded synthetic polymer globally and was found to be the most prolific emitter of both gases," according to the release. Yes, the most common type of plastic in the world, which is already subject to bag bans the world over for clogging city waterways and littering urban and rural spaces alike, is also the most detrimental. LDPE (the focus of the video below)is also used to make water bottles, six-pack rings, ketchup and shampoo bottles, and plastic "lumber." To say it's everywhere would not be an overstatement, which means this stuff is off-gassing methane and ethylene everywhere, too.

The tip of the (plastic) iceberg

And yes, there's more bad news. "This source is not yet budgeted for when assessing global methane and ethylene cycles, and may be significant," said David Karl, senior author on the study and SOEST professor in the release. That means that because this is a new finding, these gases haven't been considered when calculating and modeling future climate-change scenarios — meaning we've been missing a possibly major source of greenhouse gases.

To top it off, the greenhouse gases released by plastics are likely to continue increasing: "Plastic represents a source of climate-relevant trace gases that is expected to increase as more plastic is produced and accumulated in the environment," said Karl. As reported in the original paper in PLOS One, ".. .the [plastics] production rate is expected to double over the next two decades."

Do the companies that make plastic know of this particular environmental effect? It's impossible to know. But they certainly didn't want to talk to Royer about her findings: "I told them I was a scientist and I was trying to understand the chemistry of the plastic," Royer told the BBC. "I was trying to order some plastics of different densities and I was asking questions about the process and they all said, 'We don't want to have contact with you anymore.'"

"I think the plastic industry absolutely knows, and they don't want this to be shared with the world."

(And in case you were wondering where good-old CO2 was in this story, Royer told The Inverse that carbon dioxide is also being produced by the plastics, and she'll detail that in another paper.)

There's plenty we can do: First and foremost, we can keep pressuring food and beverage companies to come up with plastic-alternative materials that don't pollute the environment, and simultaneously hold them accountable for the waste they produce that's already out there in the world. This should not be all left up to the end user (that's us) to deal with. These companies have long known the toll their products take and they have diligently kept pumping out "convenience" plastics, fought recycling laws and initiatives whenever they could, and generally behaved as if their own profit is the only thing that matters.

We can also refuse plastic as much as humanly possible in our day-to-day lives. Keep bringing those bags to the grocery store, refusing those straws, opting for a reusable to-go coffee cup, and doing the dishes after a party instead of opting for plastic cups that will be used for 30 minutes and tossed. Keep picking trash up on the beach, and in town too (a lot of plastic gets to the ocean via storm drains). Affect change where you can — your office, your school, your neighborhood. And keep this in mind when it seems daunting. People lived much as they do today in the '40s and '50s before cheap plastics proliferated: They had graduation parties, beach vacations, picnics and drank coffee. They stored food and made complicated recipes and sipped soda.

They lived their lives without plastic, and so can we.

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.

Plastic bags emit methane, too
Dr. Sarah-Jeanne Royer at the University of Hawai'i discovered that plastic bags are contributing to global warming by giving off methane.