Well, I don’t know. But, if you are a barefooter, I do know what’s not in your carbon footprint: shoes (or at least, no where near as many shoes as the non-barefooter).
According to this article, Running’s Impact on the Earth, from the November 2008 issue of Runner’s World, a pair of running shoes and socks has a carbon impact of around 170 pounds of CO2. Leather shoes fall in about the same range.
170 pounds is about the equivalent of driving 150 miles.
A lot, however, does depend on what type of shoe is being discussed. According to this Wall Street Journal article, Six Products, Six Carbon Footprints, shoes can run from 22 pounds up to 220 pounds, depending on how they are made. If you just have to wear something, flip-flops are pretty much the lowest, with some as low as 22 pounds of CO2 per pair.
Go barefoot. Go green.