There's a lot of plastic in the ocean, but understanding exactly how much isn't easy. There's a lot of ocean out there and much of the waste is hidden from view. Despite what you may have heard, it doesn't come in the form of big garbage "patches" you can see from a boat or plane.
Scientists may be getting closer to the truth, however. A new study reports on the most comprehensive effort yet to tally the problem, and the results are shocking. There are 5.25 trillion pieces of plastic in the oceans, weighing 268,940 metric tons in all.
The research was led by Marcus Eriksen at the 5 Gyres Institute, a nonprofit in Los Angeles, along with several university colleagues. They took data from 24 marine expeditions covering 1,571 locations worldwide, then fed it into a model to estimate the total.
The Northern Hemisphere's ocean region contains slightly more than the Southern oceans (55.6% of particles), with the North Pacific being the single most plastic-polluted area. In the Southern Hemisphere, the Indian Ocean has the greatest volume, according to the study, which is published in the journal PLOS One. The greatest number of fragments were sized between 1 millimeter and 4.75 millimeters.
The estimate for floating debris is higher than previous work, including a study by Andrés Cózar, a researcher from the University of Cadiz (see here). But it's still likely to be a fraction of the actual total. The paper notes that Plastics Europe, a trade organization, estimates that 288 million tons of plastic were produced globally in 2012. That means the study's estimate is just 0.1% of production for one year. Empirically, we know that more plastic enters waterways than that.
"We stress that our estimates are highly conservative, and may be considered minimum estimates," says the study. "They also do not account for the potentially massive amount of plastic present on shorelines, on the seabed, suspended in the water column, and within organisms."
The big question is what happens to the plastic when it leaves the surface. Scientists have given various explanations, including that the micro-fragments are ingested by fish, or that it becomes dirty and sinks to the seabed.
Although there are efforts underway to gather up ocean plastic (including programs to pay fishermen to collect garbage), it's unlikely they'll make a huge dent in the problem. It may be possible to scoop up big pieces, but micro-plastics are a harder nut to crack. Activists and industry groups generally advocate more recycling and coastal clean-up to stop plastic entering waterways in the first place. If we can't clean up the water, we can at least stop adding to the burden.