In December 1997, world attention turned to Kyoto, Japan, where parties to the Framework Convention on Climate Change (FCCC) negotiated a protocol to reduce the greenhouse-gas emissions of the industrialized countries by 5 percent below 1990 levels over the next ten to fifteen years. The agreement has been attacked from both sides. Environmental groups assert that much deeper reductions are urgently needed. Opponents claim that the proposed reductions are either unnecessary or premature, would curtail economic growth, or would be unfair or ineffective without similar commitments by developing countries. Both groups overstate the importance of near-term reductions in emissions. The modest reductions called for by the Kyoto agreement are a sensible first step, but only if they are part of a larger and longer-term strategy. Indeed, near-term reductions can be counterproductive if they are not implemented in a manner that is consistent with a long-term strategy to stabilize greenhouse gas concentrations. The centerpiece of any long-term strategy to limit climate change is a transformation in world energy supply, in which traditional fossil fuels are replaced by energy sources that do not emit carbon dioxide. This transformation must begin in earnest in the next 10 to 20 years, and must be largely complete by 2050. Today, however, all carbon-free energy sources have serious economic, technological, or environmental drawbacks. If economically competitive and environmentally attractive substitutes are not widely available in the first half of the next century, it will be impossible to stabilize greenhouse gas concentrations at acceptable levels.