Let's not pretend like it's only China's problem, or only their contribution ...
This is a global issue. This represent the world fleet, not just one nation. I'm sure we benefit from the shipping of good in terms of both imports AND exports. For example, we are soon to be (if not already) the leading producer and exporter of CNG, and it get's where it's going by ocean vessel as well ...
And because these huge ships burn the lowest grades of fuel (essentially tar-like fuel that must be heated before consumed), we have to ask ourselves a few things:
1) isn't this fuel source a byproduct of the hydrocarbon fuel industry?
2) isn't a good idea, generally, to fully utilize byproducts rather than waste them?
3) if ships don't burn these fuels, what else would we do with them?
4) Would they be consumed in some other manner, or just become true waste?
5) if they be true waste products, which countries are going to be responsible to dispose of them (Oh - I think we know the answer to this one ... )
Gee - maybe the EPA can mandate a massive CAT/SCR/DFP exhaust treatment system for any of the world's fleet that would enter US waters ....
This is also why I say we focus often on the wrong things, and/or worry about trivial things. I'm NOT saying this ship-fuel topic is one to ignore, but it does put OTHER things into perspective. For example, vehicle emissions in North America. They have become so darn clean running that any progress in this field is practically moot! We've got emissions so low in North America that further efforts in reducing them do NOT provide a reasonable ROI to the consumer, or even the environment. The entire world fleet of vehicle emissions is dwarfed by the world's ocean fleet (1:260). And the world vehicle fleet is far dirtier than the North American fleet, which means the N/A vehicle fleet is a TINY FRACTION of pollution overall. Therefore, any EPA driven changes to N/A fleet emissions is pointless; it won't shift pollution issues one little iota in terms of real measurable success. What they can show in the lab as a success, won't manifest into reality on the streets because our N/A vehicle emissions is already nearly-zilch in contrast to other world industries and developing countries that we have zero control over. This is like concern over hearing-loss from the TV volume in your home when the neighbors are having a raucous block party on one side of your home, and the folks on the other side are putting in a 1/4 midget race track.