The subject of climate change is a scientific one, but it can be more than that. Environmental writer Bill McKibben, for example, is dismayed not just about the possibility of hotter temperatures, droughts, and sea level rise, but about their meaning for humankind. "We have substantially altered the earth's atmosphere," he says in his book The End of Nature (the emphasis is his). "This is not like local pollution, not like smog over Los Angeles. This is the earth's entire atmosphere. . . . The air around us, even where it is clean, and smells like spring, and is filled with birds, is different, significantly changed." 70 Other writers see global warming as simply a scientific question, one that needs conclusive evidence before action is taken. "The more I write about global warming, the more doubts I have about it,"writes Matt Ridley, a...