Woods Hole, MA - Millions of tiny bits of plastic swirl around the ocean, carried far offshore by ocean currents and with few clues about their origin. It has long been suspected that much of this plastic started out as trash on land, but exactly how much un-captured plastic waste is making its way from land to ocean has been a decades-long guessing game. Now, a team of researchers working at the National Center for Ecological Analysis and Synthesis (NCEAS) at University of California, Santa Barbara, has put a number on the global problem.
The study, co-authored by Kara Lavender Law of Sea Education Association (SEA) and principal investigator of the NCEAS marine debris working group, reported in the Feb. 13 edition of the journal Science, found between 4.8 and 12.7 million metric tons of plastic entered the ocean in 2010 from people living within 50 kilometers of the coastline. That year, a total of 275 million metric tons of plastic waste was generated in those 192 coastal countries.
Jenna Jambeck, an assistant professor of environmental engineering at University of Georgia and the study's lead author, explains the amount of plastic moving from land to ocean each year using 8 million metric tons as the midpoint: "Eight million metric tons is the equivalent to finding five grocery bags full of plastic on every foot of coastline in the 192 countries we examined."
Law, a research professor at SEA, which is home to the SEA Semester undergraduate study abroad program, explains that, "Until now, we have been estimating the amount of plastic pollution in the ocean by taking a ship far offshore, towing a plankton net, and counting each individual piece of plastic collected. This is a very tedious and expensive task." Now, researchers have taken a different approach and instead estimated the amount of plastic waste entering the ocean.
To determine the amount of plastic going into the ocean, Jambeck "started it off beautifully with a very grand model of all sources of marine debris," said study co-author Roland Geyer, an associate professor with the University of California, Santa Barbara's Bren School of Environmental Science and Management, who teamed with Jambeck and others to develop the estimates.
They began by looking at all debris entering the ocean from land, sea and other pathways. Their goal was to develop models for each of these sources. After gathering rough estimates, "it fairly quickly emerged that the mismanaged waste and solid waste dispersed was the biggest contributor of all of them," he said. From there, they focused on plastic.
Plastic pollution in the ocean was first reported in the scientific literature in the early 1970s. In the 40 years since, there have been an increasing number of reports of plastic debris found everywhere from beaches to deep-sea sediments and in Arctic sea ice. But until this study, there were no rigorous estimates of the amount and origin of plastic debris making its way into the marine environment from land.
But knowing how much plastic is going into the ocean is just one part of the puzzle. With between 4.8 and 12.7 million metric tons going in, researchers like Law are only finding between 6,350 and 245,000 metric tons floating on the ocean's surface.
"This work gives us a sense of just how much we're missing," Law said, "how much we need to find in the ocean to add up to the total. There is a lot of plastic sitting on the bottom of the ocean and on beaches worldwide. Right now, we're mainly measuring plastic that floats, and only in relatively few locations."
SEA scientists and undergraduate students in the SEA Semester program continue to add to long-term data sets of floating plastic debris in both the Atlantic and Pacific Oceans. "The several thousand SEA Semester students who have collected and counted plastic debris since the 1980s have been essential contributors to our understanding of the scale and scope of this pollution problem," said SEA president Peg Brandon. "Not only are students sailing to regions never before sampled for plastic debris on our newly expanded trans-Atlantic and South Pacific cruise tracks, but they are gaining a first-hand understanding of the human impact on the oceans."
Jambeck forecasts that the cumulative input of plastic waste to the oceans will equal 155 million metric tons by 2025. The planet is not predicted to reach global "peak waste" before 2100, according to World Bank calculations.
"We're being overwhelmed by our waste," she said. "But our framework allows us to also examine mitigation strategies like improving global solid waste management and reducing plastic in the waste stream. Potential solutions will need to coordinate local and global efforts."
About Sea Education Association/SEA Semester®
Sea Education Association (SEA) is an internationally recognized leader in undergraduate ocean education. For nearly 45 years and over one million nautical miles sailed, SEA has educated students about the world's oceans through its Boston University accredited study abroad program, SEA Semester®. SEA/SEA Semester is based on Cape Cod in the oceanographic research community of Woods Hole, Massachusetts and has two research vessels: the SSV Corwith Cramer, operating in the Atlantic Ocean, and the SSV Robert C. Seamans, operating in the Pacific.