In a previous post, I calculate ground vehicle CO2 emissions using the following formula: number of miles driven per week * weeks in a year) / average vehicle fuel efficiency * pounds of CO2 emitted per gallon, which is about 20 pounds (go to for explanation of formula). So, for instance: assuming we drive 20,000 miles a year and our vehicle gets an average of 35 miles a gallon, our annual emissions would be roughly: 20,000 miles/35 = 571 x 20 = 11,420 pounds of CO2 a year. How does ground vehicle travel compare with air travel? It depends on how long the flight is (given that cruising emits less CO2 than take off and landing). Here’s one formula:

Short flight of 500 miles x .64 lbs/mile = 320 pounds of CO2 (640 pounds roundtrip) Medium flight of 1600 miles x .44 lbs/mile = 704 pounds of CO2 (1408 pounds roundtrip) Long flight of 3000 miles x .39 lbs/mile =1170 pounds of CO2 (2340 pounds roundtrip)

So one roundtrip flight across the US would be about 2000 pounds of CO2, or a bit over 1/5 of driving 20,000 a year at 35 mpg. Overseas travel puts us in a whole ‘nother league, emission-wise: 15,000+ miles round trip from San Francisco to Calcutta – or about 6 months of vehicle travel at the pretty good 35 mpg.

For perspective, when planning your travels.... and remember: the more stops, the more emissions.