Carbon Offsets vs. Fuel Efficiency

A while back I posted a piece with my take on evaluating the cost of driving a highly fuel efficient car versus a normal car.  For my evaluation, I utilized information for a Prius, a Ford Focus, and a Smart fortwo.  I determined that, in my opinion, the Prius would not pay for itself in 3 years under normal driving costs and conditions.  In fact, at $3.95/gallon gasoline and 20,000 miles per year of driving, the Focus proved to be almost $2000 dollars less expensive to own.

 

Today, I pulled up to a stoplight and saw a Prius in the lane next to me.  I started thinking about whether or not the Prius was cost effective to own compared to my used, mid-sized sedan (probably not, since I only paid $13,300 for my car), when a thought hit me.  The impact of owning the Prius is beyond the economic value.  There is also an environmental impact in the reduced carbon-dioxide emissions.  But, what if I decide to try and offset my carbon-dioxide emissions through the purchasing of credits?  Would that make my car more expensive to own than the Prius?

 

First, I pulled up some information on what the emissions levels of cars are.  Thanks to a handy-dandy spreadsheet calculator assembled for the Progressive Auto X-Prize contest (based on EPA GREET numbers), I determined that my car, at 25 miles per gallon, produces greenhouse gas equivalent to 101 pounds of CO2 per 100 miles driven.  So, in a 20,000 mile year, I would produce approximately the equivalent of 20,200 pounds, or about 10.1 tons, of CO2.

 

Next, I went to Carbonfund.org to determine the cost of the necessary offsets to effectively neutralize my emissions.  If you look at the auto calculator on their site, they sell carbon credits for $10 per ton of CO2.  (Interestingly, they calculate emissions differently, so I would only have to offset 7.1 tons according to their calculator.)

 

So assuming my 10.1 tons of CO2 at $10 per ton, I would have to purchase $101 of offsets per year to completely neutralize my CO2 emissions from driving.  A Prius would only reduce a little more than half of those emissions.

 

That makes my used 25 mpg car look like a great value!