[filleokus]

Container ships are tremendously energy efficient, around 30 gram per tonne-km.

Some back of the envelope math:

- Distance China to US East Coast ≈ 10 000 km

- Weight of 1 toothbrush = 10 gram = 0.0001 tonne

30 g * 10 000 km * 0.0001 tonne = 30 gram of Co2

30 gram of Co2 is the amount of Co2 emissions from ≈ 100 meter of travel with an average car.

Of course there is secondary land transport from the port etc. But even though the sea shipping industry is one of the biggest Co2 emitters (not to speak of other nasty stuff [0]), it's still incredibly energy efficient.

[0]: You saying the ships are "diesel-spewing" is actually doing the ships a favour, it's usually heavy fuel oil.