We study the effectiveness of emission targets under the Kyoto Protocol with respect to reducing CO 2 emissions. Using country-level and US state-level panel data and employing the synthetic control method, we find very little evidence for an emission reduction effect for the major emitters among the Annex B countries with binding emission targets. More generally, we also show that evaluating the effectiveness of international environmental policies at the country level comes with a number of empirical challenges that may invalidate findings based on more traditional panel data approaches.