arundhati roy's india is home to 17 of the world's 25 most polluted cities; and not coincidentally theld's fastest growing major economy. what is it normally like in delhi? >> roy: well, normally it is dystopian, you know? especially in the winter months. sometimes that smog is not just outside your house, it's inside your house, inside the rooms, you know? so that's how terrible delhi is. and suddenly we're just seeing blue skies. >> wertheim: and it's like this, from shanghai to secaucus. by circumstance and not design, a glimpse of life with fewer fossil fuels, nd already the clean and quiet surroundings have found favor with wildlife. what does that tell you about the earth's ability to rebound and snap back? >> mckibben: well, maybe we still have a window to-- to take a step back. and if we do, maybe the earth will meet us halfway. >> wertheim: and when people say, need to get thisstar we need to jump back on planes. this climate change, that can wait," what do you say? >> mckibben: well, it obviously can't wait. you've got to pay attention to reality or else you end up getting bi