It seems to me this is the de facto situation of most environmentally conscious people. A good first step is to acknowledge that baby steps are OK as long as they are on a good trajectory, and you show people around you that you can admit the facts to yourself without immediately falling into a funk of bad conscience and apathy.
Sure, I bike, I recycle, and I take public transit instead of driving. But I know that this doesn't change the world. It just reduces my contribution to the problem, and that is sufficient for me.