Originally Posted by JohnBrooking
I think it's actually much worse. If you burn those 6 pounds of hydrocarbons, the added oxygen from the air that's fueling the fire is now being paired up with the carbon to actually producte 20 pounds of CO2. So for every gallon of gasoline you burn, you emit 20 pounds of CO2. If your car gets 20 MPG, this works out very nicely to 1 pound per mile.
If you read my earlier post again, you'll see I said the air used in the combustion process is a wash, since it came from the atmosphere to begin with.
For conversation, I'll accept the 20 lbs of CO2. And I'll explain that the C came from the 6 lbs of gasoline, and the 14 lbs of O2 came from the atmosphere. Thus, the net increase in atmospheric carbon is <drum roll please> six pounds. In other words, 14 of your 20 pounds was already in the atmosphere to begin with.
Don't take this the wrong way, I'd rather have that O2 floating around by itself, not bonded with a C.