The point is the local transportation accounts for the significant majority of carbon emissions from freight transportation. Moving goods 3000 miles by ship and another 100 miles by road is not much more emissions than moving goods only 100 miles by road.

A more effective change would be to make transportation emit less greenhouse gases. Get hydrogen powered container ships and electric vehicles. This would reduce greenhouse gases significantly more, and wouldn't involve destroying the global economy.

I like this comment. I do believe the global logistics industry will adapt to a low carbon future, rather than dismantle itself (and the world economy). In short, it is a death sentence for their business. And no business wants to go bankrupt, so they will adapt -- at least: try to.

Do you think ammonia or hydrogen is more likely to be used for ships? At this time, I am leaning towards ammonia because storage and infrastructure is simpler.

Funny side note: While writing this post, I was doing a bunch of Google searches about ammonia, hydrogen, and blue vs green. Every single search returned a single ad from Saudi Aramco touting their blue ammonia and hydrogen capabilities. Incredibly depressing. The non-petro states need to hurry up and cover the center 80% of Australia with solar panels (Chilean Andes and North Africa too) to produce whatever green industrial inputs we need from "thin air". Maybe we can run a bunch of carbon sequestration machines too. In parallel, we can drive up carbon taxes.

My perspective is that Ammonia is a storage mechanism for hydrogen. The question is more like cryogenic vs compressed air vs chemical (such as ammonia, or hydrogen peroxide). A bigger question is production: solar, hydro, and wind are probably cheapest for electrolysis. Thermochemical production may make sense for nuclear or geothermal based power. Maybe Iceland becomes a big gas station for transatlantic shipping, based on geothermal energy?

I like your idea about Iceland. They are already a major aluminium smelting hub due to extremely cheap thermal energy.

Forget container ships: if you want to reduce greenhouse gases, you need to target trucks, trains, and cars first, then probably aviation after that. Container ships are ridiculously low-emission in terms of CO2/tonne.

No, they don't. Container ships produce less CO2 per tonne than trains, by a large margin.