The key insight of Gaia Theory is that the entire Earth functions as a single living super-organism. But according to James Lovelock, the theory's originator, that organism is now sick. It is running a fever born of increased atmospheric greenhouse gases. Earth will adjust to these stresses, but the human race faces a severe test. It is already too late, Lovelock says, to prevent the global climate from “flipping€ into an entirely new equilibrium that will threaten civilization as we know it. But we can do much to save humanity. In the tradition of Silent Spring, this is a call to address a major threat to our collective future.