This quick CO2 calculator is kind of interesting.
However, it turned out not to be terribly useful for us. The average American CO2 output is 9.44 tons per year. I came in over 22! But 15 of it was due to air travel, and only 7 for the rest of our lives, which is below average. Basically, I entered that each of us flew a single time a year, but since we are in Hawaii, those flights are 7+ hours and killed my footprint.
At the end, it gives some ideas on reducing carbon emissions, but there's nothing you can do for a single flight once a year from Hawaii often at the mandate of your employment. I'm not going to take the train instead!