Analyzing the Role of Customary International Law in Shaping States’ Obligations to Climate Change Mitigation

Climate change law has predominantly been structured around international treaties and institutional mechanisms derived from the United Nations Framework Convention on Climate Change (UNFCCC). In this context, the role of customary international law has remained largely underexplored. However, customary international law—independent of states’ explicit consent to treaty obligations—can serve as a binding source for establishing duties related to the mitigation of climate change. This study seeks to address whether customary international law plays a role in shaping state obligations concerning climate change mitigation. If so, what is the nature of these obligations, and how do they relate to treaty-based climate commitments? To answer these questions, the research first identifies the relevant customary obligations within public international law. It then examines their applicability to climate mitigation efforts and explores the interaction between customary norms and treaty-based obligations. The study asserts that there is no inherent conflict between customary international law and climate treaties; rather, their relationship is interpretative. In its final part, the research analyzes the mutual influence between customary norms and climate treaties in the domain of climate change mitigation. The practical value of this inquiry lies in its potential to interpret existing judicial decisions on climate change from a perspective independent of treaty law and state consent, thereby offering a conceptual basis for anticipating future rulings within the same framework.