The government of Quebec this week instituted a carbon tax on gasoline, diesel, natural gas and heating oil. What I found interesting is that the tax on diesel fuel is slightly higher (9/10 of cent per liter) than on gasoline(8/10 of a cent).

I though that the more energy dense diesel fuels (along with more efficient diesel engines) would emit less CO2 per gallon consumed, but that's not the case, according to the U.S. EPA:

CO2 emissions from a gallon of gasoline = 2,421 grams x 0.99 x (44/12) = 8,788 grams = 8.8 kg/gallon = 19.4 pounds/gallon

CO2 emissions from a gallon of diesel = 2,778 grams x 0.99 x (44/12) = 10,084 grams = 10.1 kg/gallon = 22.2 pounds/gallon

So while the amount of CO2 emissions per mile driven is likely less with diesel fuel/engines, the tax is appropriate per fuel consumed.

What this calculation doesn't consider, however, is the amount of CO2 emissions generated in refining the different fuel types. It historically has required less energy to refine diesel than CO2, although perhaps extracting the sulfur for the cleaner fuel evens that out a bit.

At the other end of the spectrum we have Michigan Congressman John Dingell proposing a 50 cent per gallon tax on gasoline while nothing on diesel. Obvious that unfairly gives diesel car/truck operators a free ride. A slight difference in the fuel tax relative to diesel's approximately 15 percent better fuel efficiency is more appropriate.