According to the book SuperFreakonomics, which was released this past week and I highly recommend, suggests the ultimate form of going green is eating kangaroo, rather than beef.
Why is this?
Cows, sheep and other livestock emit through their exhalation, farting, belching and manure, a methane gas that is about 25-times more potent as a greenhouse gas than the carbon dioxide released by cars (and humans). These animals are responsible for about 50% more greenhouse gas than the entire transportation sector.
However, kangaroo farts don't contain methane, so you want to help your environment in one of the best ways possible? Instead of that Big Mac, try a little Kangaroo on for size. From what I've heard, the Aussies hate them anyways.