It's usually talked about in broader contexts. There are some fuel modes (air travel being the really obvious one) that aren't ever going to be non-combustion.

It's usually talked about in broader contexts. There are some fuel modes (air travel being the really obvious one) that aren't ever going to be non-combustion. You have to put carbon into the upper atmosphere to move people in jetliners, period. So solutions would involve either synthesizing carbon-neutral fuel, or burning petroleum and offsetting it by putting the same amount of carbon back into the ground somewhere else. There's a reasonably strong argument that the latter is more energy-efficient. But it's all infant tech and no one really knows.