My earlier post on calculating carbon impact definitely spawned a lot of comments and follow-up conversations. These talks made me realize a few things.

First, I've decided that the online calculators that I linked to earlier are not really the best way to calculate carbon load. For example, they focus on the individual, whereas I now believe that one's entire family or household should be considered. For example, the heating and electric bill for my condo is really divided among two people. Further, my girlfriend doesn't own a car, so if we need to drive somewhere, it's in my car. These details are lost unless we consider the household and not the individual.

Second, it's so ridiculously easy to get the actual usage numbers for utilities that everyone should just calculate their actual carbon load rather than using the online estimators.

So, with these two things in mind, I used the following conversion factors to calculate our carbon impact (all information from carboncounter.org):

• 19.36 pounds CO^2 per one gallon gasoline burned
• 0.968 pounds CO^2 per one mile flown
• 1.3925 pounds CO^2 per one kWh electricity used
• 12.0593 pounds CO^2 per one therm natural gas used

I then gathered my actual usage numbers as follows (all figures are for the trailing twelve months ended February 2007):

• Car: Looked at my car emissions certificate from 2 years ago, which lists my mileage at the time, and compared it with my most recent car emissions certificate. [10,000 miles total over 2 years, or 5,000 miles per year]
• Electric: Obtained monthly kWh usage from portlandgeneral.com [11,074 kWh]
• Natural gas: Obtained monthly therm usage from nwnatural.com [139.7 therms]
• Air travel: Obtained actual mileage flown (for personal trips only!) from my frequent flier statements. [12,354 miles each for me and Aimee]

Using the above information, a formula for computing annual household carbon load using actual usage numbers is:

19.36(Car miles driven)/(Car MPG) + 1.3925(kWh electricity used) + 12.0593(therms natural gas used) + 0.968(Air miles flown)

Which, for us, translates to:

19.365000/27.5 + 1.392511074 + 12.0593139.7 + 0.96812354*2

For a grand total of 44,543 pounds of carbon dioxide for both me and Aimee (22,304 pounds each).

This concludes the assessment phase. Next up: Atonement phase :)