A lot of Chinese ships burn spent USA motor oil (illegal to burn in the USA) on the way home, ergo, free trip home! And the entire smoke plume lands in the USA . .

Do you have a source for that, I can't seem to find a reliable one

Sulfur dioxide emissions at sea are not that damaging compared to in land. They did make some zero emission cargo ships but it was pretty expensive due to crew complement for the reactor.

Interesting. There is only one operational cargo ship powered by a nuclear reactor - https://en.wikipedia.org/wiki/Sevmorput

Next year it will enter into force the IMO regulation on a global sulphur cap, vessels can only burn a low sulphur bunker (the fuel for a commercial ship). http://www.imo.org/en/MediaCentre/PressBriefings/Pages/13-su...

You are wrong. Even in terms of emissions ships are the most efficient way to transport goods, in terms of km-tonnes.

I appreciate that you cited a paper, but I think you are overstating. The paper discusses CO2 emissions, which indeed are lower for transport by ship than by trains. But the parent was talking about "environmental damage" from ships that burn the "nastiest, most sulphrous and damaging forms of crude oil", and thus was referring to pollutants other than just CO2.

This report, for instance (I have not read it completely) says "Rail is generally the cleanest mode of transport for most pollutants" and "Maritime shipping is one of the cleanest mode of freight transport, except for PM and specific sulphur oxide (SOx) emissions". While there is lots of emphasis currently on CO2 emissions, other pollutants are also worth considering.

https://www.eea.europa.eu/data-and-maps/indicators/specific-...

Granted the US and EU could agree to regulate emissions from container shipping.

UN is doing something already. By January 2020, the limit for Sulphur in fuel oil used on board ships operating outside designated emission control areas will be reduced to 0.50% m/m (mass by mass).

http://www.imo.org/en/mediacentre/hottopics/pages/sulphur-20...