Significantly more than 20 times I'd bet. The airframe will have to be significantly reinforced to support a design where the maximum takeoff weight is equal to the maximum landing weight. At that point, aerodynamics start to look a lot more like a rocket equation where you can't dump stages.
I think medium to long term, nuclear or renewable powered synthetic fuel is far more likely, especially since we already have a lot of generic infrastructure applicable to fossil fuels and carbon taxes could be the thing that pushes synthetic fuel into the market.
This doesn't require alien technology, it just requires carbon to be priced so that it isn't artificially cheaper than existing alternatives.
The state of biofuel today leaves a lot to be desired as far as the ability to scale without causing other environmental disasters, and many of them aren't even carbon neutral.
As for nuclear cargo ships -- I'd love to see them, but the liability and political hurdles are insane. You'd probably need a really big carbon tax before we'd see them.
Even without nuclear, container ships don't have major weight restrictions (they already weigh a hundred thousand tons), so you can fuel them with anything that will catch on fire. Make carbon expensive and they'll just buy whatever is the next cheapest -- sawmill residue, seaweed, whatever. A lot of the difficulty with "biofuels" is the process of making them into oils that can directly replace petroleum in road vehicles, but large ships don't need that. A large furnace like that can burn unprocessed solid biomass.
Although, burning biomass in ocean-going vessels is not necessarily a net positive. If, for example, they start burning sawmill scraps which were previously being pressed into Ikea furniture, you're just replacing one carbon emission with another. Biofuels are complicated; you have to be careful not to offset sequestration, as well as being cognizant to other emissions generated both in the process of generation and in burning them. Because of the tangential effects, some biofuels emit more carbon than oil!
We have some of the problems solved. While batteries are energy dense enough to support passenger cars, there's still a lot of progress to be made before the tech can meet the demands of shipping/bulk-cargo/intercontinental transport. For example, batteries still need to be 20 times more dense before we can build a cargo/passenger aircraft with one.