> it could well be that the cheapest option is to absorb their emissions from the air and inject them into the ground, rather than producing carbon-neutral jet

> it could well be that the cheapest option is to absorb their emissions from the air and inject them into the ground, rather than producing carbon-neutral jet fuel I am not sure if you want to capture carbon or just CO2. If you want just to capture CO2, that's a different consideration but there is AFAIK no scalable technology that can store CO2 reliably. So what you need to do is to actually break the C-O bonds in CO2, which is very energy expensive. In theory you could burn methane (natural gas) or other hydrocarbon in system (airplane) A, producing more energy than needed by system (factory) B, which would recapture carbon from the air and convert it to pure carbon. That way, you would produce net energy by burning hydrogen into water (methane and carbon, respectively, are the most efficient choices for this). Somebody can calculate it precisely based on the enthalpy, I am sure, but it seems to me that the both systems together would have to be at least 40% efficient (that is the product of their energy efficiencies would have to be that) for this to be energy positive. I don't think anybody has demonstrated this level of efficiency yet, and it might well be impossible (if we also consider the dispersal of CO2 in the atmosphere, as somebody else has noted). Assuming this is possible (unlikely), in practice this would also require the operator of the system A to pay (at least) the cost of energy used by the operator of system B for the recaptured carbon. And this can be a practical problem, because people cheat in various ways and they would probably lobby to pay less at the expense of the environment. It seems much more transparent solution is just to forbid drilling for hydrocarbons outright. That's why one should be careful about using dollars for these calculations. All externalities are rarely counted in costs. It is easy to fool yourself or other humans this way, however, the nature cannot be fooled.