As the Copenhagen climate conference approaches, our 'heads talk about how to confront global warming. David W. Orr, author of the new book "Down to the Wire," debates Jim Manzi about the appropriate response to the uncertainties of future climate change. David argues that passing the cap-and-trade bill is crucial—but still not enough. Lester Brown, author of the new book "Plan B 4.0," and David Roberts of Grist wonder if America can mobilize against climate change as we did against a more immediate threat during WWII. Lester rejects the "all of the above" approach, making the case that nuclear energy and clean coal are the wrong path to pursue.