Two decades have passed since the Clean Air Act Amendments of 1990 launched a grand experiment in market-based environmental policy: the SO₂ cap-and-trade system. That system performed well but created four striking ironies: First, by creating this system to reduce SO₂ emissions to curb acid...

This paper summarizes recent empirical research on compliance costs and strategies and on permit market performance under the U.S. acid rain program, the first large-scale, long-term program to use tradeable emissions permits to control pollution. An efficient market for emissions permits...

Global climate change, and policies to slow it or adapt to it, may be among the primary forces shaping the world's economy throughout the next century and beyond. Nonetheless, popular treatments of this issue commonly ignore economics. This introductory essay sketches some of the uncertainties...