Heavy oil ships are already being banned from numerous ports. That will only accelerate. Shipbuilders are gearing up to build anhydrous ammonia fueled replacements.

Anhydrous ammonia will be produced at massive scale in tropical synthesis facilities for delivery worldwide. This is why long-term storage is not considered important.

Not ships are banned, but usage of heavy fuel. That means the last few hundred miles ship goes using diesel. But in international waters any kind of fuel could be used.

And that is about to change as well.