Well even if these ships need to switch fuel to a much cleaner variant, when nearing shore (or a harbor) they non the less pollute the city they are harboring in massively when machines are running on low power to "just" provide the necessary energy for the ship. Most harbors currently do not have supporting energy lines for these big ships. So at least some people in these cities get impacted by these ship emissions directly.

I once worked shortly for a company running tourist ships and have to say I was shocked to learn how dirty this kind of travel is. I never thought about that until I learned that the ship they built while I was there was considered clean, because it was the first to have a particulate filter prototype (that had some hick ups in the beginning due to changing salt levels in the surrounding water).

Interestingly sulfur dioxide has a net cooling effect on the atmosphere: https://earthscience.stackexchange.com/questions/9805/would-...

However this effect does not outweigh the health consequences of emitting this pollution, or the contribution it makes to acid rain and other serious problems.

CO2 isn't a particulate but I would say it is slightly misleading for a different reason - car particulate requirements are pretty damn strict to the point diesels are the dominant source despite being a road minority. The numbers for cruise ships would ironically look way better in the 70s when us automakers were still trying to claim it was unreasonable to require the exhaust not smell of unburnt gasoline. And that was before catalytic converters were essentially mandatory.

A more apples to apples comparison would be in trucks or buses - granted all should be improving as well.

Also, it's only NOx and SOx pollution where the ships beat the cars. In terms of carbon dioxide pollution, the pollution from all ships in the world is utterly dwarfed by the pollution from cars.