To get a sense of how fuel consumption affects the environment, consider this: Every gallon of gas used on the roads produces 20 pounds of CO2. That’s because when gas burns, its carbon and hydrogen elements separate, and each carbon atom (molecular weight of 12) combines with two atoms of airborne oxygen (16) to form CO2 (44). Thus, the carbon portion of a gallon of gasoline, which weighs about 5.5 pounds, yields roughly 3.7 times that weight in CO2, or 20 pounds. (This number is a bit low, because some CO2 is produced during the extraction, refining and transport of the gas before it reaches your tank.)
Daniel Becker, a Washington-based environmental consultant, said that if Congress had pushed through its 1990 plan to increase average fuel economy standards to 40 miles per gallon by 2001, the United States could save 3 million barrels of oil each day. Crunching the numbers (assuming the standard 42 gallons of gas per barrel of oil), that translates into roughly 919,800,000,000 fewer pounds (or 418 million fewer metric tons) of carbon that would have been released into the air this year had the standards been adopted.
As Brendan Bell, Washington representative of the Union of Concerned Scientists, noted, "It would have been a remarkably different world on a variety of fronts."