I recommend that California water down its fuels with - water. I’d say about 10% watered down by 2020 should do the trick. This will definitely produce fuels with 10% less carbon output, probably a whole lot less, actually.
Water is a very beneficial substance (so far at any rate), being natural, renewable, and plentiful.
I’d suggest that the introduction be done very slowly so that the current generation of carbon-burning power plants and engines have a chance to get use to the full 10% amount. By 2020, with a full 10% dilution, Californians will have tremendous reason to rejoice from the low amount of carbon emanating from their engines and power plants.
In short, I could go on and on about the virtues of water as a fuel additive for California, but I think that most right-thinking people will agree with me that this is the fuel additive most suited for California.
Only bottled water, not dirty tap water.