8 Million Tons of Plastic Lands in the Ocean Every Year

Humans are throwing enough plastic into the world's oceans to cover Manhattan in coffee stirrers and plastic bags, 34 times over.

We've been hearing for a while about the increasingly dire problem of discarded plastic that's going into the world's oceans, where it poses a threat to the environment and aquatic life. But now, the urgency is driven home by a new study published in the journal Science that reveals just how much plastic humans are putting into the world's waters.

Based on coastal population densities, plastic consumption and waste-handling practices, researchers calculate that it comes to 8 million metric tons of plastic trash.

To get your head around your number, think of it this way. At the annual meeting of the American Association for the Advancement of Science in San Jose, Calif., the study's lead author, Jenna Jambeck, an assistant engineering professor at the University of Georgia, held up a plastic trash bag. "Think of five bags filled with plastic for every foot of coastline in the world," she said.

That's enough plastic to cover an area 34 times the size of Manhattan in an ankle-deep layer, according to Roland Geyer, an industrial ecologist from the University of California-Santa Barbara, whose National Center for Ecological Analysis and Synthesis orchestrated the study.

Or maybe this is more surprising: On the low end of the estimate of between 4.8 and 12.7 million metric tons -- the amount of plastic dumped in the ocean would be equivalent to the tonnage of tuna that fishing boats catch each year, worldwide.

"We're taking out tuna and putting in plastic," said co-author Kara Lavender Law, a research professor at the Massachusetts-based Sea Education Association.

Worse yet, with plastic consumption on the rise, by 2025, the cumulative amount of plastic that's been dumped in the ocean -- some of it washing up on shorelines -- since its widespread use began in the 1950s could reach 155 million tons.

Nicholas Mallos, director of the marine debris program at the Ocean Conservancy in Washington, D.C., who was not involved in the study, said it was important because it calculated how much plastic is ending up in the oceans, rather than relying on the portion that can be observed on the surface of the water.

"It's one to three magnitudes greater than we had expected," he said.

The study found that the top five countries in terms in terms of aquatic plastic waste were Asian countries with a combination of dense coastal populations, rapid economic growth and inadequate waste collection and disposal practices. China topped the list, with between 1.32 million and 3.53 million metric tons of plastic annually. Indonesia, the Philippines, Vietnam and Sri Lanka rounded out the list.

The United States ranked 20th, with between 40,000 and 110,000 metric tons of plastic waste.

The world produces about 275 million tons of plastic waste per year, but much of it is buried in landfills. Even in the United States, only 9 percent of the plastic waste is recycled, according to the Environmental Protection Agency. Only a few percent of the total waste is tossed into rivers and other waterways and ends up in the oceans, but that's enough to become a major environmental problem, the study shows.

Exactly what happens to all that plastic once it gets into the ocean remains unclear, the scientists said. Another study, published in PLOS ONE in 2014, concluded that as much as 250,000 tons of plastic -- some 5.25 trillion pieces of various sizes -- is floating on the ocean surface.

Some believe that much of the rest is sinking to the ocean bottom or being broken down by microorganisms. But an even bigger worry is that some of the waste breaks down into tiny -- sometimes even microscopic -- pieces called microplastic, which is being consumed by aquatic animals ranging from worms to whales. The scientists said that some of it eventually will make its way into the human food chain and there is some evidence that it's already happening.

What to do about the plastic is an even more troubling dilemma. Mallos said that the most important priority is to reduce the amount of plastic that's being discarded by improving collection and recycling practices in countries that produce the most waste. Once that input is reduced, he said, it might be possible to gradually collect much of the waste that's already in the water.

One group has proposed the use of floating barriers to trap and remove the plastic on the surface. But as Geyer noted, removing plastic that's already sunk thousands of feet to the ocean floor would be difficult and undoubtedly costly. Removing microplastic from the water without harming plankton and other marine life is another challenging problem.

The National Oceanic and Atmospheric Administration (NOAA) is celebrating "30 Days of the Ocean" in the month of June, and in honor of the organization's hat-tip to life undersea, we take a look, this final June weekend, at some of the organization's captivating marine life snapshots. Here, the eyes of a queen conch (

Strombus gigas

) peek out from under its shell in La Parguera, Puerto Rico.

PHOTOS: 30 Days of the Ocean

Kelp and sardines, just doing what they do, off Anacapa Island, Channel Islands National Marine Sanctuary.

Whales Get Fishing Tips From Peers

This school of permits contains 60-80 individuals, each more than a foot long. The school was observed in the Dry Tortugas, Florida.

PHOTOS: Shipwreck Hunt Turns Up 'Tar Lilies'

A Caribbean spiny lobster strolls on the sea floor. This photo was shot during a 2010 NOAA expedition in the U.S. Virgin Islands to map underwater habitats and the marine life they support.

Deep-Sea Methane Ecosystem Found in Atlantic

DNA testing confirmed that the eggs pictured here were those of a loggerhead turtle, a marine reptile species listed as threatened under the Endangered Species Act. The testing was done by NOAA's Center for Coastal Environmental Health and Biomolecular Research, in Charleston, S.C., the only lab in the country dedicated to forensic analysis of marine species.

PHOTOS: Sea Turtles From Shell to Surf

This manta ray coasts over a reef, in the process inviting much smaller fish to clean parasites and other debris off of it. Manta Rays are the largest type of ray in the ocean.

The World's Biggest Manta Ray Sanctuary Created

Make way for the balloonfish, also known as a porcupine or spiny puffer fish. As its name suggests, it will swell up like a balloon when attacked.

VIDEO: Flushed Fish Invading Oceans

Here we see a close-up of brain coral in the Dry Tortugas, Florida.

Off the California coast, a group of elephant seals sleeps in the sun on a sand dune on Active Point, San Miguel Island, part of the Channel Islands National Marine Sanctuary.

With its distinctive reddish and white stripes, its gracefully flowing fins, and its menacing spine, not many fish can embody the beauty, mystery, and danger of the ocean quite like the lionfish. Although it's native to the Indo-Pacific region, lionfish were introduced to the Atlantic and are now found along the U.S. coast, from North Carolina to Florida, and in the Bahamas and Caribbean. The lionfish spells trouble for the balance of ecosystems and fisheries it invades, as it can out-compete native species for food and space. It lacks predators, has a voracious appetite, reproduces quicly, and is spreading fast.