Container boats are ridiculously carbon efficient because they move unimaginable amounts of weight (amortizing any fixed costs like keeping the engine running) slowly (low drag) over a perfectly level surface (no loss from going up hill).

Almost any carbon reduction scheme that involves doing anything other than using them doesn’t work.

For instance, the embodied carbon of an apple that goes from China to the US, then is driven to a Walmart in a diesel train / semi is probably lower than the carbon footprint of one from the local farmers market (unless the farmer drives the apples to market in an EV and the local power grid is low carbon).