Ocean currents have been carrying floating debris into all five of the world's major oceanic gyres for decades and scientists have revealed that 8 million tons of plastic clutters oceans each year.
The rotating currents of these so-called "garbage patches" create vortexes of trash, much of it plastic. However, exactly how much plastic is making its way into the world's oceans and from where it originates has been a mystery, until now.
The study found that more than 4.8 million metric tons of plastic waste enters the oceans from land each year, and that figure may be as high as 12.7 million metric tons. That's one to three orders of magnitude greater than the reported mass of plastic floating in the oceans. A metric ton would be equivalent to 1,000 kilograms or 2,205 pounds.
Roland Geyer, an associate professor at UCSB's Bren School of Environmental Science and Management said that using the average density of uncompacted plastic waste, 8 million metric tons, the midpoint of our estimate, would cover an area 34 times the size of Manhattan ankle-deep in plastic waste.
According to the study, countries with coastal borders, 192 in all, discharge plastic into the world's oceans with the largest quantities estimated to come from a relatively small number of middle-income, rapidly developing countries.
In fact, the investigators found that the top 20 countries accounted for 83 percent of the mismanaged plastic waste available to enter the ocean. They went on to say that reducing the amount of this waste by 50 percent would result in a nearly 40 percent decline in inputs of plastic to the ocean.
Knowing how much plastic was going into the ocean was just one part of the puzzle. Millions of metric tons reach the oceans, yet researchers are finding between 6,350 and 245,000 metric tons floating on the surface, a mere fraction of the total. This discrepancy is the subject of ongoing research.
The NCEAS working group forecasts that the cumulative impact to the oceans could be as high as 155 million metric tons by 2025. However, the planet will not reach global "peak waste" before 2100, according to World Bank calculations.
The researchers suggest achievable solutions that could reverse the alarming trend in plastics being dumped into our oceans. Among them, according to the study, are waste reduction and "downstream" waste management strategies such as expanded recovery systems and extended producer responsibility. According to the researchers, while infrastructure was being built in developing nations, "industrialized countries can take immediate action by reducing waste and curbing the growth of single-use plastic."
The study is published in the journal Science.