More than 5 trillion plastic particles weighing 268,940 tons are estimated to be floating in Earth’s oceans. The new estimate, published today in PLOS ONE, is based on models of floating plastics data gathered from a series of 680 surface net tows and 891 visual surveys from oceans around the world. Currents and winds push the plastics around the world’s oceans, concentrating many of the pieces in five massive midocean gyres in the northern and southern Atlantic, the northern and southern Pacific, and the Indian Ocean. Despite having fewer inputs—due to smaller coastal populations—the amount of plastic in the gyres in the Southern Hemisphere was of similar magnitude to that in the north. That hints that ocean currents may redistribute material between the gyres more easily than thought—or that the most abundant particles, called microplastics (less than 4.75 millimeters), disappear from the sea surface more quickly in the Northern Hemisphere, the researchers found. Based on how plastics break into smaller fragments, the scientists had expected to see even more microplastics than they counted; those missing microplastics, they suggest, could sink more easily below the surface, become stranded on shorelines, be eaten by animals, or break down more rapidly under ultraviolet light from the sun.