International environmental agreements and imperfect enforcement: Evidence from CITES

International environmental agreements address global environmental problems such as the decline in biodiversity. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) regulates international trade in wildlife to prevent its decline. Discussions about CITES' effectiveness abound, but evidence is lacking. We combine the largest available panel database on wildlife populations with the history of countries' membership and species' protection under CITES. We find that after more than 20 years of a species' inclusion into CITES, wildlife populations increase by about 66% in countries with thorough enforcement, irrespective of whether trade in the species is only restricted or completely banned under CITES. Our results suggest re-focusing discussions away from whether CITES should partially restrict trade or impose a complete trade ban, and towards better enforcement. More generally, we find that enforcement is crucial for effective international environmental agreements.