We compare the short-run and long-run effects of environmental reform and harmonization under autarky and free trade. When trade is driven by environmental distortions rather than real relative advantages, harmonization of environmental policies, even if achieved by lowering standards in one country, can improve short-run aggregate welfare. With the possibility of multiple steady states, long-run considerations favor a "race to the top" rather than a "race to the bottom" even when upward and downward harmonizations...