barbara g. fleischman. and by our sole corporate sponsor, mutual of america, designing customized individual and group retirement products. that's why we're your retirement company. >> welcome. in our last broadcast i promised you more of david simon, and i'll keep that promise down the road, but right now, because of the news, my guest is a journalist turned activist who is often asked, how can you remain so optimistic and so energized when you've taken on nothing less than the threat of global catastrophe? it's a question he's even heard from me, and more than once, because i've known him for years now as both colleague and friend. after all this time, bill mckibben's stamina and soulfulness continue to amaze me. we met over a decade ago on a canoe trip together for the making of my series "america's first river," about the history of the hudson and the struggle to save it from industrial pollution. >> in the fall, and the winter, and the spring, it's pretty lonely, beautiful place. >> i had read his clas