Everyone knows there’s a lot of plastic in the ocean — there’s the famous garbage patch, and the photos of albatross bodies full of plastic. But as it turns out, there’s way more plastic than we thought. About 5 to 13 million metric tons of plastic flowed into the ocean in 2010, according to a study from a group of oceanographers, engineers, ecologists, and other researchers published in Science today. That’s 20 to 20,000 times as much as we knew was floating on top of the ocean, Sea Education Association investigator Kara Lavender Law said during a press conference announcing the findings.

A lot of the plastic sinks to the ocean floor or floats in the water column. There’s plastic in Arctic Sea ice and plastic on beaches around the world. Much of it breaks down into tiny, even microscopic pieces, which get eaten by organisms that we sometimes consume ourselves; the consequences of that are still being studied.

The source of the problem isn't mysterious: there’s a lot of plastic in the ocean because humans use a lot of plastic. The amount is staggering. Plastic has only been in wide use for about 65 years, yet it’s outstripped production of almost every metal, University of California Santa Barbara professor Roland Geyer pointed out during the conference. The 192 coastal countries included in the study produced 275 million metric tons of plastic waste in 2010. A significant amount of that ended up in the ocean.

To illustrate what eight tons — the middle range — looks like, University of Georgia professor Jenna Jambeck held up a large shopping bag filled with plastic at the conference. "That’s the same as five bags like this filled with plastic for every foot of coastline in the world," she said. By 2025, she said there would be the equivalent of 10 bags per foot of coastline entering the ocean each year.

The study also ranks the main offenders. They were mostly countries with rapidly growing economies that haven’t developed good waste management programs yet. China lead by a long shot, then came Indonesia, the Philippines, Vietnam, and Sri Lanka. But then there was the United States, whose large coastal population and high use of plastic placed it at number 20, despite having by far the best waste management system on the list.

Getting the plastic out of the ocean isn’t feasible, the researchers concluded, so we need to keep any more from getting in. They suggest two tactics. The first is to get rapidly expanding countries like China to institute better waste management programs. The second involves getting wealthy countries like the United States to stop generating so much plastic waste.

Either of these approaches could do a lot of good. A 50 percent increase in effective waste disposal by the top 20 countries would result in a 41 percent drop in mismanaged plastic waste by 2025, whereas a decrease in per-capita plastic generation to something closer to the 2010 average for the top 91 countries would result in a 26 percent decrease. For that reason, Jambeck said she was optimistic, though the way she expressed her optimism seemed cautious at best.