Extreme sports run the gamut when you consider environmental impact. Some, like motocross, snowmobiling and Red Bull air racing come with a heavy environmental footprint while others, such as skateboarding and BMX, are more benign. Some are even more green, often requiring nothing more than the shoes on your feet, the calluses on your hands, or the wife on your back. If you're going to risk life and limb in pursuit of a good adrenaline rush, here's how to do it without wrecking the environment. (Text: Shea Gunther)