[lukehutch]

Presumably when the ethanol is burned, all the captured carbon is released again... So you have to re-capture each time you use it.

[jsmcgd]

Roughly speaking, if the carbon is captured from the atmosphere and later released into the atmosphere, the technology is carbon neutral.

If the carbon is sequestered (stored permanently) it is carbon negative.

If the carbon is obtained from an unsustainable source and released to the atmosphere it is carbon positive. The current consensus is that only carbon positive systems are considered a problem.

[dna_polymerase]

That's true, and the reason why we need healthy oceans and rain forests. They are carbon dioxide sinks and store carbon for eons.