Kyoto-type accords and carbon markets are designed—almost as analogues to Keynesian “pump-priming”—to bridge the shortfall between spontaneous decarbonization and the emissions targets required by each scenario. Although the IPCC never spells it out, its mitigation targets necessarily presume that windfall profits from higher fossil-fuel prices over the next generation will be efficiently recycled into renewable energy technology and not wasted on mile-high skyscrapers, asset bubbles, and mega-payouts to shareholders. Overall, the International Energy Agency estimates that it will cost about $45 trillion to halve greenhouse gas output by 2050.9 But without the large quotient of “automatic” progress in energy efficiency, the bridge will never be built, and IPCC goals will be unachievable; in the worst case—the straightforward extrapolation of current energy use—carbon emissions could easily triple by midcentury