text: Those hypotheses may be summarized as follows. First, man s increased use of fossil energy is warming the earth significantly. Second, the impact of such warming will be catastrophic and rapid. Third, the scheme to coordinate global energy use reductions worldwide is feasible and effective. Fourth, if we do it smart, it won t cost much. Finally, energy rationing will provide greater safety than concerted efforts to make societies freer, wealthier, and, thus, better able to ride out the shocks and surprises of an unknown future. Note that the mere fact that the Earth might be warming, or that mankind might be causing such warming, does not in itself clinch the case for an international climate treaty.