The application of common but differentiated responsibilities in the global governance of marine plastic pollution: a study in the context of the global plastics treaty negotiations

Marine plastic pollution is a problem that crosses borders and needs immediate global cooperation. This kind of cooperation needs to be based on a single international framework that fairly and authoritatively divides up responsibilities while respecting national sovereignty. Although the Fifth United Nations Environment Assembly initiated an intergovernmental negotiating committee to develop a legally binding Global Plastics Treaty by 2024, no agreement has been reached by the fifth session in 2025. Key issues persist surrounding plastic source control, financing mechanisms, and raw material regulation. This paper examines how the principle of common but differentiated responsibilities (CBDR) can apply to global marine plastic governance. This study first examines the doctrinal foundations of the principle of common but differentiated responsibilities (CBDR) and explains why it is relevant to marine plastic pollution. It then analyses the main points of contention surrounding CBDR in the ongoing plastics treaty negotiations, including debates over differentiation, obligations, and implementation. Finally, it reviews state and institutional practice at the national, regional, and multilateral levels to assess how CBDR is applied or contested. The analysis shows that CBDR remains contested in marine plastic governance. Problems include the instrumental use of CBDR by different actors, inconsistencies in responsibility differentiation, outdated categorical groupings, interpretive disagreements, and deadlock over means of implementation. These issues limit CBDR’s ability to support an effective plastics treaty. Based on these findings, the paper proposes strategies to apply CBDR better. These include improving procedural rules, developing a dynamic and tiered responsibility system, designing a framework with core and flexible obligations, and establishing comprehensive support and monitoring mechanisms. In summary, these measures can illustrate the potential for CBDR to move beyond its divisive role and serve as a more nuanced governance tool for reconciling diverse national interests and capacities. Such an approach could contribute to laying the groundwork for an effective and universal plastics treaty by enabling a fairer allocation of responsibilities.