For today you have container ships, which offer cabins for paying cutomers. However I am not sure that that is better then flying, given how bad cruise ships are for the enviroment.

I did a quick check on costs about ½ year ago. Room and board on a cargo ship is the cheapest non-DiY option AFAIK, which is around $100/day. Crossing the Atlantic in one is ~2—3 weeks. So I think we’re talking $1400 min. for the Atlantic, whereas the cheapest one-way economy flights are ~$500 if you shop it out. So then the question is, couldn’t the difference if $900 be spent in a way that more than offsets the emissions difference between a cargo ship and a flight?

I realize the OP asked about crossing the Pacific, which I guess means the price gap would be even bigger.

Oh, I forgot to mention I read about a bus that goes from London to New York. IIRC it takes a month because it goes the long way around (ferry to continental Europe, east into Russia and to Alaska). Not sure if the ocean between Russia and Alaska freezes well enough or if that’s by ferry. Not sure what the price is either, but a guess the bus would have the lowest emissions.

EDIT: just noticed the OP nixes travel via dictatorships, so that would nix the bus.