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Thanks for your comment, which is provocative and ideological but respectful. I will answer in the same spirit. Sagan deliberately did not follow the criterion which is now often quoted, "Extraordinary claims, require extraordinary evidence." But I wouldn't go so far as to call Nuclear Winter a fraud. It was a worst case but plausible scenario that made people rethink their advocacy of the Mutually Assured Destruction theory of the arms race. It was an important factor, though hardly the only one, in the movement toward arms reduction treaties. Hansen and others speaking of the tipping point in climate change are careful to state that their worst case scenarios are not definite predictions but rather plausible outcomes with consequences too dire to be ignored. Some people on the left-wing side of this argument might agree with your statement that "Sagan sold out," but they might view the sellout as giving credit to religion, as Billions and Billions does. You might also be interested in my comparative review of two Sagan biographies. Both of those discuss his reasons for promoting the Nuclear Winter hypothesis. He was the least important of the scientific contributors of the paper usually denoted as TTAPS for its five authors, but certainly the most active in promoting its conclusions. It has always puzzled me why religious conservatives have not spoken up about their concern for the planet. Could it be that they decided not to push the issue because it went against the interests of their big-business political allies on other social issues (abortion, gay marriage, etc.)? I'm glad they are finally speaking out on this. Preserving a viable planet is not a liberal or conservative issue. It is based on a scientific consensus that is no longer disputed except by those with vested interests in the status quo. (Though everyone denies vested interests.) Thanks again for opening this thread of discussion. I hope others will join in. Fred Bortz -- Science and technology books for young readers (www.fredbortz.com) and Science book reviews (www.scienceshelf.com)