This is the way it is in several Europen cities (if not all). The cruise ships burn very pollutingly fuels while in "international waters" but when they enter a port they are required to use cleaner fuel. Those regulations are there.

But nothing regulates what they do in international waters.

"All ships shall keep a record of which fuels they have burned. Each time a ship docks in a European port, the log shall be submitted to the customs enforcement unit at that port. The enforcement unit shall tally the amount of dirty fuel burned since the ship last docked in Europe.

"A ship that has burned X dirty fuel shall be charged $Y Euros per liter burned. If a ship is found to have created fraudulent logs, it shall be charged $Y*10, or seized. There is a reward for reporting such fraud leading to seizure equal to 10% of the forfeiture."

Or something like that. As long as the penalty is financially meaningful compared to the income of the ship's engineer, you would quickly start to have trouble getting away with using such fuel.

Couldn't they be required to turn over logs of fuel (type? uncertain how it works) use along with some form of inspections?

By definition the port of arrival has no jurisdiction on what the ship does in international waters.

No, but they're also under no obligation to allow the ship to dock. Any ability to enforce standards ultimately derives from this option.

Could ports regulate what fuel the ship is carrying, even if it's not burning that fuel while in port? For instance, if a cruise ship is burning clean fuel because it's near port, but is carrying a great deal of dirty fuel for use when it gets back into international waters, could the port fine the operators of that ship for merely possessing the dirty fuel?

You could ban them from having any dirty fuel in their tanks at all.

The ban would be applied by the country where they are registered - the flag of convenience. These are already usually poorer countries that offer lax regulations in exchange for the registration fees.

The problem would be that if one country enacted a ban, all the ships registered there would just switch to some other country without the ban (or that usually skipped that inspection), and the original country would lose out on a bunch of much-needed cash.

It might be more effective to tax the dirty fuel at the source, so that it becomes uneconomical to the ship operators to use the dirty fuel in the first place.

Of course, such a regulation should at least be Europe-wide and apply when the ship is in your harbour (or territorial waters). Taking a detour to refuel elsewhere takes time. I am unsure how you would check for it, though. Conversely, I have no idea how taxing fuel at the source could ever work, since that source can easily be in countries you have no control over.

Now all we have to do is convince acid rain to stop at national borders.

Yes, you can do that, and countries do. Ships will burn cleaner fuels when they are in territorial waters for this reason. The problem is they're still doing environmental damage out in international waters.

What you need to do is put the foot down and prevent flags of convenience (or more specifically, those that fail to meet environmental standards) from docking at your ports at all. Which I'm not sure is permissible under maritime laws.

(or maybe there is some dodge like preventing the ship from "carrying hazmat" which you define as bunker fuel, or ban ships from having soot in their stacks that has sulfur deposits, or so on...)

Yes, but Barcelona (where I live) would not do anything that could hinder tourist money. As an example, almost no stores are allowed to be open on Sundays by law. But they made an exception close to the port because enough tourists get off the boats for a day or 2 during the weekend and want to shop.

Its a hard battle to "force" any of these cruise lines or shipping for that matter, to change. It would have to be a EU law, etc etc, but thats 5+ (probably 10+) years to get passed.

It doesn't matter at all where they are flagged. They still have to comply with local regulations everywhere they operate. The US just fined Carnival $20M for dumping pollution in the Bahamas, and threatened to ban them from all US ports. It's a slap on the wrist, but it's one small example of how they can be punished regardless of where they're flagged.

"Does it matter how the ship is flagged?" - Probably not for large fleets, see [0] for examples of how this might be applied to the 2020 change.

Your ship may be registered to a tiny little island that won't enforce any regulation, but there's a limited number of markets to underwrite the insurance you need, and you'll want to dock at major sea ports.

[0] https://uk.reuters.com/article/us-shipping-fuel-sulphur/new-...

The newest cargo ships and tankers that operate in Western Europe aren't really the problem.

Cruiseships have been ignored for a long time because tourism=money.

This could be done through the Paris MOU yes. The term is "Port State Control" and the way it works is that when you get to a Port, the Port State, not your Flag State has a say in whether you can enter and leave.

As originally conceived the Paris MOU was about labour standards. European ports didn't like the fact that "Flags of Convenience" (legally, "Open Register" countries, where you can register a ship without any relationship to that country) were allowing ships in their register to have crew that weren't meeting European labour standards. Long working hours, poor pay, no healthcare and so on.

But by coincidence, as the meeting to sign the MOU was starting a terrible accident happened. Suddenly the headlines were about this nasty shipping accident, and you've got a bunch of people in Paris negotiating a new international agreement, so... today the Paris MOU is very interested in safety, with worker rights being a subsidiary consideration (after all if you're at the end of your fourth 16 hour shift this week you're probably not terribly safe if you're even still awake) but it also created this idea of Port State Control now seen in similar institutions around the world.

The US already de facto exercises Port State Control, and has laws which effectively bar foreign ships from doing a lot of stuff in US territory anyway - it could make a pollution regulation today if it cared, which obviously at least the Trump administration does not. But PSC wasn't really a thing anywhere else before the Paris MOU.

That would just incentivize ships to not dock in EU countries. For freight this might be an issue but for leisure cruises not so much.