David Gessner on "My Green Manifesto"

David Gessner wants to change the way people write about nature.  Instead of the traditional stories about wild animals in pristine landscapes, he calls for a style of nature writing that's messy, even raucous, and includes an often-overlooked animal:  people.  He talks with Anne Strainchamps about his book "My Green Manifesto," the story of a kayak trip down Boston's charles River with his friend Dan Driscoll.