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 i

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).