Plastic pollution in the ocean is a big problem, but we don't know exactly where it all comes from or how it disappears over time. Researchers used computer simulations and real data to figure out that there is much more plastic in the ocean than we thought - about 3 billion kilograms, not just 250,000 tonnes. They also found that a lot of plastic ends up on coastlines and sinks down, or breaks into smaller pieces. By studying the Dutch North Sea and the Mediterranean Sea, they were able to estimate the total amount of plastic pollution in the global ocean.