I've given some thought to how my hobby affects the environment. I prefer to use natural fibers, which I think is helpful. Every time a new natural option is offered (bamboo, maize) I make sure I try it. I'm learning to spin and want very much to use my own yarns to make things. It seems to me that moving closer to the beginning of the yarn-making process is easier on the environment.
Anything that keeps us from having to use excessive energy seems good. I never go out to buy yarn unless I've got other errands to run in the same area as one of my LYS. Knitting itself doesn't use much, except for lights for knitting at night.
I need to learn more. Very few activities are completely harmless. How can I continue to knit and reduce the environmental impact? What kind of effect does the dye have when I use it to dye yarn? Are animals harmed in any way when their hair is harvested for our yarns? What other things am I doing that I could do differently?