An estimated 150 million tonnes of plastics have accumulated in the world's oceans and the problem increases, as waste management and recycling systems are unable to cope with the rising plastic production. Marine plastic pollution has consequences on the global ecosystem, coastal communities, industries including tourism, shipping and fishing and its impacts on food security and human health remain unknown. Negative effects span borders of national jurisdiction and a solution to the problem requires international cooperation. Policies to prevent plastic pollution have been implemented on local, national, regional and international levels. However, efforts to adequately address the problem have failed so far. When faced with such transboundary problems that threaten global public goods in the past, states have formed international regimes through negotiating legally binding treaties to effectively cope with the issue. This thesis examines factors for success and failure of international regimes for the protection of global public goods and investigates two cases of one successful and one unsuccessful international regime to cope with transboundary pollution problems. Results of the analysis of the successful Montreal Protocol show that an advantageous cost-benefit analysis, active leadership of actors pushing for an agreement, support by non-state actors on the domestic level, as well as perceived urgency for action were success factors. The treaty design constituted a necessary condition for success by using the following treaty elements: a) common but differentiated responsibilities, b) trade restrictions, c) financial mechanism, and d) adjustments and amendments. Findings from the Kyoto Protocol case study indicate reasons for failure, namely the disadvantageous cost-benefit analysis, perceived unfairness due to the exemption of developing countries from costs, domestic compliance incapacity, as well as inadequate targets to address the problem. The treaty design was a necessary condition for failure of the regime by including: a) one-sided responsibility, b) an inadequate scope to deal with the problem, as well as mechanisms that allowed for loopholes and complicated monitoring, c) rigidity incentivising short-term policies and preventing innovation, as well as d) lack of compliance and enforcement mechanisms. This thesis demonstrates that treaty design is significant for setting incentives for participation and compliance, as well as for deterring non-compliance.
The treaty design of a successful international agreement to eliminate marine plastic pollution would require the use of: a) the principle of common but differentiated responsibilities, b) an adequate scope to address the problem by including land- and sea-based sources, as well as chemical additives and all stages of the life-cycle of plastics, c) issue-linkage to international plastics trade, d) a financial mechanism to support developing countries, e) flexibility to adapt to changes, f) effective reporting, monitoring and review procedures, and g) enforcement through incentivising compliance and deterring non-compliance. This research demonstrates that treaty design is a key determinant for success of international regimes. This thesis contributes to research by reviewing academic literature on the emergence and maintenance of international regimes, mapping the problem of marine plastic pollution and identifying treaty elements that will contribute to success of a legally binding mechanism on the global scale to adequately address marine plastic pollution. Implications go beyond the topic of marine plastic pollution and global environmental problems, and can also be useful for academics, policymakers, and civil society actors in other areas of international law and global governance.