Faced with the growing threat of climate change, policymakers and regulators have increasingly sought ways to reduce greenhouse gas emissions. Cap-and-trade programs have become a popular policy option that sets a limit on overall emission levels but allows firms to trade emissions permits, thus creating market incentives for firms to reduce greenhouse gas emissions. These programs have been implemented in California, the northeastern United States, Europe, China, and elsewhere. Existing research suggests that these initiatives have been effective. In California, for example, recent evidence shows that facilities subject to cap-and-trade have reduced their greenhouse gas emissions by 3?9 percent.