Does hydrogen have anything to offer over synthetic petroleum as a vehicle fuel?
Synthetic petroleum is produced from coal, oil and natural gas, carbon energy sources that don't help reduce environmental footprint.
Last I looked, a hydrogen fuel cycle was slightly more efficient than a gasoline fuel cycle. But it's a lot easier to handle gasoline than hydrogen. We already have the equipment to move and store gasoline all over the country, no cryogenics needed.
(I say "gasoline" but things like methanol are also suitable.)
Sure - exactly as much carbon dioxide, in fact, as was removed from the atmosphere when the fuel was produced.