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1. INTRODUCTION
In contrast to the Kyoto Protocol 1 and most other multilateral environmental agreements (MEAs), the Paris Agreement establishes very few substantive legal obligations. For the most part, the Paris Agreement relies on the ‘ambitious efforts’ that parties must ‘undertake and communicate’ as ‘nationally determined contributions [(NDCs)] to the global response to climate change’. 2 Intended NDCs (INDCs) had been communicated by most parties to the United Nations Framework Convention on Climate Change (UNFCCC) 3 in advance of the Paris summit. (I)NDCs must cover all main areas of international cooperation as defined in the Paris Agreement, including mitigation, adaptation, financial support, transfer of technology, capacity building, and transparency. 4 This innovative approach was intended to overcome the opposition of some states to a treaty that had too many substantive provisions. It also successfully navigates the diplomatic complexities of securing negotiated national commitments in a context where there are as many conceptions of differentiation as there are parties to the UNFCCC.
However, international lawyers have divergent views on how (I)NDCs should be characterized. (I)NDCs do not fall squarely within any of the classical sources of international law outlined in the Statute of the International Court of Justice (ICJ) – namely, international conventions, international customs, and general principles of law. 5 Different views have therefore been expressed regarding the obligations of states under the Paris Agreement in respect of NDCs. This question, however, has typically been dealt with only briefly, as a digression in studies on the legal nature of the Paris Agreement itself. 6 In recent years this treaty and the continuing negotiations regarding its modalities of implementation have been the primary focus of the literature on international law and climate change. Nevertheless, given that the Paris Agreement itself imposes very few substantive legal obligations, the legal characterization of (I)NDCs is a question of paramount practical importance.
This article identifies and analyzes the international law obligations that arise in relation to (I)NDCs. It argues that such obligations may arise in two distinct ways. On the one hand, treaty obligations arise under the Paris Agreement, inasmuch as it creates an obligation to pursue the mitigation objectives that NDCs define. On the other hand, communications such as (I)NDCs may be among the unilateral declarations that international courts...