[Myrddin]

The firm tells drivers that for $49.99 they can make up for the 12,000 tons of carbon a typical sedan or station wagon produces in a year.

12,000 tons = 24,000,000 pounds...that's 24 million pounds! Gasoline weighs 6 lbs/gallon, so that is 4 million gallons of gas...assuming all of it converted to carbon dioxide. At 20 miles per gallon, you'll have to drive 80 million miles a year. The person who wrote this story must have been the valedictorian at a California high school.

[Myrddin]

The outrageous claim is concocted by noting that gasoline is 87% carbon/13% hydrogen. One gallon of gas weighs 6.25 lbs. 6.25 * 87% = 5.5 lbs of carbon. Now the trick. The carbon is tied to two atoms of oxygen to make CO2. Adding the weight of the oxygen turns the 5.5 lbs of carbon to 20 lbs of CO2.

Let's re-do the calculation. 24 million pounds of CO2 divided by 20 lbs / gallon = 1.2 million gallons of gasoline per year. At 20 miles / gallon, that is a mere 24 million miles per year.

I still say the article was written by the valedictorian of a California high school.