But I don't want to focus on airplanes here, but shipping, as the thread title might indicate. Not only ships burn low grade cheap fuel full of cancer and asthma causing pollutants, such as sulphur oxides, but they do so on a very, very inefficient fashion. And they aren't even fast as airplanes to compensate. Indeed, the ~15 largest cargo vessels, alone, emit more of those polutants over a year than the combined car fleet of the entire world (close to 800 million vehicles nowadays).
That's actually a pretty old number. We're at around 1.3 billion right now.