You are one of seven billion people on Earth. Whatever you or I do personally—eat tofu in a Hummer or hamburgers in a Prius—the planet doesn't notice. In our confrontation with climate change, species preservation, and a planet going off the cliff, it is what several billion people do that makes a difference. The solution? It isn't science, politics, or activism. It's smarter economics. The hope of mankind, and indeed of every living thing on the planet, is now in the hands of the dismal science. Fortunately, we've been there before. Economists helped crack the acid rain problem in the 1990's (admittedly with a strong assist from a phalanx of lawyers and activists). Economists have helped get lead out of our gas, and they can explain why lobsters haven't disappeared off the coast of New England but tuna is on the verge of extinction. More disquietingly, they can take the lessons of the financial crisis and model with greater accuracy than anyone else the likelihood of environmental catastrophe, and they can help save us from global warming, if only we let them.