Four years ago, climate change was hot. Politicians from both parties, pressed by an anxious public, seemed poised to act. But that was then. Today, public opinion about the climate issue has cooled and politicians either ignore the issue or loudly proclaim their skepticism of scientific evidence that human activity is imperiling the planet. What's behind this reversal? FRONTLINE correspondent John Hockenberry, of PRI's The Takeaway, goes inside the organizations that fought the scientific establishment, environmental groups, and lawmakers to shift the direction of debate on climate issues and redefine the politics of global warming.