[IndubitableCoil]

Because we can convert all produced carbon dioxide from a Starship back into methane using the Sabatier process [1].

[1]: https://en.wikipedia.org/wiki/Sabatier_reaction

[lukealization]

Why isn't SpaceX doing that then? Why isn't any airline doing that then? Oh look, it's cheaper to use refined natural gas from a well. That's why. In the absence of either properly priced externalities, the market will always choose the cheapest option—Sabatier-generated Methane is not remotely comparable in price to fossil nat gas.

Mentioning theoretical solutions doesn't help if they will never be used practically.

[rstupek]

I don’t think airliners use Methane?

[lukealization]

Aircraft use hydrocarbons which require similarly intensive chemical processes to create the fuels from the same constituent ingredients as the Sabatier reaction.