I swear to God, I've read the article twice and I've read the comments replying to your question and I still have no idea.

I think the problem is that, for any given sentence, it is unclear whether the author is talking about the fuel a ship is burning to move its cargo, or fuel that the ship is transporting to a destination.

I do understand that the article is making some kind of distinction between the two, but it is so terribly written that it's just impossible to figure out which one it's talking about at which point. Or at least I certainly don't care to waste my time "solving" the article like it's some kind of linguistic puzzle.

I'm not sure I've ever come across an article that needed an editor to improve its clarity more than this one.

It's saying that 40% of the tons of cargo loaded onto ships is fossil fuels, but this makes up about 50% of ton-miles, because fossil fuels travel further on average than other cargo. Not the easiest headline to correctly parse.

From the fucking article: Fossil fuel cargoes travel long distances in very large flows, so their decline removes more than a proportional share of cargo mass. It removes a larger share of the ocean work and the fuel burned to do that work.

And if I can get on my soapbox. This same problem (carrying fuel to feed the transportation unit) is well studied in medieval England because it was one of the main determinants of where cities and castles were placed (albeit unknowingly at the time). And we see what happened in England when they were able to get out from under feeding oxen.

It means in the long term there might be more efficient ways to ship 'energy'. If you ship containers full of solar PVs, batteries and use it over their lifetime the amount of 'total energy' transported for a given unit of energy to transport the materials might be an order of magnitude or more higher

That is not what I understood from the article. What I understand is:

Fossil fuels are 40% of freight tonnage, but transporting them fuels is responsible for 50% of the total freight fuel consumption.

I assume 99% of freight uses fossil sources as fuel.

It’s trying to say what if we didn’t have to haul energy around from place to place but generate it closer to consumption - we could move more useful stuff instead.

It is so weird that it makes 40% sense of 50% its length.

So 10% is a lot.

The preposition ("butt") is wrong