Tony Haymet, former director of the Scripps Institution of Oceanography, has heard hundreds of ocean cleanup plans. Late at night, over many beers, he's come up with a few dozen of his own. None of them, he says, has seemed likely to work.

That includes this spring's offerings. A Dutch engineering student, Boyan Slat, envisions a contraption with massive booms that would sweep debris into a huge funnel. Songwriter and music producer Pharrell Williams wants to fund the monumental cost of any cleanup by turning recycled ocean plastic into yarn and then clothes.

The challenge is huge. For one thing, the garbage is spread over millions of square miles. For another, it's made up mostly of degraded plastic, broken down by sunlight and waves into tiny bits the size of grains of rice.

Climate 101: Oceans

"That's what makes it so horrifying," Haymet says. "The micro-plastic is the same size as the stuff living in the water column. How would we ever go out and collect it? So far no one's come up with a plan to separate all the micro-plastic from the living life that's the same size."

In the face of growing criticism, Slat had to back off his optimistic boast that he could clean up the oceans in five years. He posted a notice on his website asking the media and the critics to wait until he finishes his research.

Meanwhile, the garbage keeps growing.

Consider this alarming statistic from CSIRO, Australia's national science agency, which is wrapping up a three-year study of marine debris: Every decade global production of plastics doubles. Even if someone came up with a workable collecting mechanism, how much impact could it have?

"If we are doubling what we are putting into the ocean on a ten-year basis, there's no way to keep up," says Chris Wilcox, an ecologist at CSIRO. "It would be as if you were vacuuming your living room, and I'm standing at the doorway with a bag of dust and a fan. You can constantly keep vacuuming, but you could never catch up."

View Images Trash litters a beach in Aruba. Photograph by Paul Souders, Corbis

The Garbage Patches

Most of the garbage accumulates in five little-explored "patches" found in the doldrums of the Atlantic, Pacific, and Indian Oceans.

The largest is the Great Pacific Garbage Patch, which starts a few hundred miles off the coast of North America and stretches to a few hundred miles off the coast of Japan; a more concentrated area lies between California and Hawaii.

One commonly accepted estimate is that the high-density area inside the Great Pacific Garbage Patch contains 480,000 pieces of plastic per square kilometer (nearly four-tenths of a square mile). But scientists say that's only a guess.

View Images Altogether the globe's garbage patches contain 200 million tons of floating debris. Photograph by Scripps Institution of Oceanography, UC San Diego

Charles Moore, who "discovered" the Great Pacific Garbage Patch in the late 1990s and plans a research trip there in July, estimates that altogether the globe's garbage patches contain 200 million tons of floating debris. He came up with the figure based on calculations that 2.5 percent of the world's plastic ends up in the sea.

Marcus Eriksen, a marine scientist and co-founder of the California-based 5 Gyres, which studies the five main garbage patches, estimates the total floating debris is just 500,000 tons.

In either case, the harm to fish and other sea creatures is increasing. A 2009 research trip to the Great Pacific Garbage Patch by Scripps found 9 percent of the fish had ingested plastic. Eriksen, with help from seven other scientists, recently analysed material in all of the garbage patches. Of 671 fish collected, 35 percent had ingested plastic particles.

"Either number scares me," Haymet says. "Those are only the sick fish—not the ones who died because they ate plastic that was too big. And they are the only two studies. There should be hundreds of studies of this stuff. Our life, our economies are totally dependent on the oceans. Fifty percent of the oxygen we breathe is made in the ocean every night."

View Images A scuba diver investigates a pile of discarded toilets on the seafloor. Photograph by Floris Leeuwenberg, The Cover Story/Corbis

Addressing the Problem

Haymet and like-minded ocean scientists haven't given up. They favor a low-tech, more practical approach to protecting the oceans from trash: Persuade the world's people to stop littering.

Only about 20 percent of ocean plastic comes from marine sources, such as discarded fishing equipment or cargo ship mishaps. About 80 percent of it washes out to sea from beach litter or was carried downstream in rivers, according to the CSIRO study, which is considered the most comprehensive.

About half of that litter is plastic bottles. Most of the rest is packaging.

"All of that stuff was in a human's hand at one point or another," Wilcox says. "The essence of the solution is to provide incentives for people not to throw this stuff away. It is the cheapest, simplest, and far most efficient solution to the problem."

Creating incentives to help reduce littering can be a political challenge. Only one of Australia's eight main states and territories has a beverage-container deposit law, says Britta Denise Hardesty, who conducted the CSIRO study.

In the U.S. only ten states—including California, Maine, Massachusetts, and Connecticut-have enacted container deposit laws. Opinion polls show support for such laws, but beverage manufacturers have opposed legislation. They argue that bottle deposits are more expensive than other forms of recycling and that requiring deposits constitutes a tax, which increases the cost of beverages.