Sometime before the end of this century, if nothing changes, the carbon dioxide concentration in the atmosphere will double from its pre-industrial level. If doubling carbon dioxide levels leads to a 2.7°F average temperature increase—the lower bound of the climate-sensitivity estimate—then the world has many decades to cut fossil-fuel use sharply. Societies can take their time and move carefully. But if doubling carbon dioxide levels causes a rise of 8.1°F, the transition must be much faster—a disruptive slam-down of the brakes. The two courses are completely different. What should societies
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Sometime before the end of this century, if nothing changes, the carbon dioxide concentration in the atmosphere will double from its pre-industrial level. If doubling carbon dioxide levels leads to a 2.7 ° F average temperature increase—the lower bound of the climate-sensitivity estimate—then the world has many decades to cut fossil-fuel use sharply. Societies can take their time and move carefully. But if doubling carbon dioxide levels causes a rise of 8.1 ° F, the transition must be much faster—a disruptive slam-down of the brakes. The two courses are completely different. What should societies do?
