If you're pulling carbon from the atmosphere, the process would theoretically be carbon neutral. I think this is one of the goals for SpaceX's Starship vehicle

If you're pulling carbon from the atmosphere, the process would theoretically be carbon neutral. I think this is one of the goals for SpaceX's Starship vehicle. In practice, I'd have reservations about widespread manufacture of methane. Existing methane infrastructure is often leaky and methane itself is a far more powerful greenhouse gas than carbon dioxide. That isn't to say that manufacturing methane shouldn't be considered, but it's extremely shortsighted to say that methane manufacture is the only storage technology that should be considered.