On a snowy winter morning five years ago, after four days of cocooning in the hospital, I walked home carrying my newborn daughter. I knew I was crossing the threshold into life as a mother, caregiver, and working parent. What I didn't know was that I was about to become a different kind of environmentalist. It took just a few blocks to transform my environmentalism from one based on vehement philosophical and political beliefs to one grounded in the humility of everyday experience. And it took just a little while longer for me, armed with a newfound sense of constituency, …