I was going to say that the administration of this might be difficult, so I completely accept your points above. The reason I chose flights and home heating sp

I was going to say that the administration of this might be difficult, so I completely accept your points above. The reason I chose flights and home heating specifically was that they are some of the easiest to administer, since governments already track which unique individuals are buying which flights, and home heating is naturally tied to an address (although I suppose someone might own a second home, with the gas bill paid in their spouse's name). For something like car travel, we may (unfortunately) reach a point where everyone's journeys are tracked, or at least where odometer readings have to be regularly submitted to the government. It wouldn't be too hard for the government to aggregate those numbers by registered owner, but it does assume that there is a fixed conversion between miles travelled and CO2 emitted, which breaks down if synthetic fuel becomes an option.