"The study was conducted last summer and its findings released in February. Lead researcher Daniel Lack of Noaa's Earth System Research Laboratory at the University of Colorado determined that the 51,000-odd commercial vessels now plying the world's oceans spew almost as much air pollution as half the total number of automobiles on the planet.
"'It was definitely a surprise for me when we pulled those numbers out,' Lack said in an interview. 'These ships are emitting as much [pollution] as 300m cars. It's a hidden giant.'"
So the average is one shiip = 6000 cars. Obviously, some ships will be much worse. But for the article that started this to be right, all of the maritime pollution is down to 6 ships. Seems really unlikely.
Another megabytes the dust.