Ten years ago I wrote a book called The End of Nature, which was the first book for a general audience about the question of global warming. At the time, climate change was a hypothesis. By burning fossil fuels and thereby emitting great quantities of carbon dioxide, human beings would trap heat near the planet's surface, changing its weather. A strong hypothesis, but a hypothesis nonetheless. The appropriate response to that hypothesis was more study, general concern, and the beginning of modest action in the event that the hypothesis was correct. I was, on the one hand, extremely scared by the research I'd done; on the other hand, I was confident that, at the very least, a serious discussion was under way.