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The U.S. environmental movement has devoted immense effort and political capital to blocking Keystone XL, the pipeline that would bring bitumen from Canadian oil sands to Gulf Coast refineries. James Hansen, the most visible climate scientist to turn anti-carbon campaigner, declared it "game over" for climate change if the pipeline is approved. Yet Keystone is a far from obvious focus for the limited campaign resources available to protect our climate. Oil-sands fuels emit about 10 to 20 percent more carbon than conventional oil over their life cycle. Suppose Keystone is blocked, or suppose that technical fixes (see "Alberta's Oil Sands Heat Up" ) eliminated that extra carbon. Neither outcome would make a big dent in emissions. The root of the climate threat posed by fuels is the carbon emitted when they are burned for transportation. Emissions from vehicles account for more than three-quarters of the life-cycle emissions of petroleum fuels. To solve the problem, we must decouple transportation from petroleum.