These ships are mostly out in the middle of nowhere...
I don't see half a million people hanging on the side of the boat sucking down exhaust.
I really don't understand why a lot of the attacks on emissions in the last 6 months or so, have been on diesel engines, which are usually the "greenest" form of ICE... extremely low greenhouse gas emissions for the energy produced (if you're the type that cares about that), and we can use so many fuel sources other than dinosaurs.
Let's try this...
Two identical cars, one diesel, one gasoline; both in a sealed garage for an hour.
I'll take the diesel.
I'll walk out with a bad cough for a week or so, and die at 89.5 instead of 90.
You won't walk out.
So again, other than some bureaucrat screaming, and counting on the "commoners" not having any sense of scale (let's face it, thousands, millions, billions... how is that different from "one, two, many"?) this is someone with a product to sell trying to guilt us into buying it.