Obligations under the Paris Agreement- Analysis of ICJ’s Climate Change Advisory opinion – Indian Blog of International Law

Rahul Mohanty

Background

On 23^rd July 2025, the International Court of Justice (‘ICJ’) delivered a landmark advisory opinion on the issues of obligations of states in respect of climate change, unanimously holding that states have legal obligations to ensure protection of the climate system, and explained these obligations and consequences for their breach. The advisory opinion finds the obligations from various sources, including climate treaties (UN Framework Convention on Climate Change (read its analysis here), Kyoto Protocol (read its analysis here) and Paris Agreement on Climate Change), other environmental treaties, human rights conventions, and customary international law. This piece will focus on the Court’s analysis of the obligations of states under the Paris Agreement.

Giving teeth to the Paris Agreement

The ICJ made several remarkable observations regarding the Paris Agreement, which are likely to have significant implications. Commenting on the relationship between the three climate treaties, UNFCCC, Kyoto Protocol and the Paris Agreement, the Court noted that the obligations in the Paris Agreement are complementary to and are intended to give a more concrete substance to the principles and obligations outlined in the UNFCCC. It rejected the argument of the Paris Agreement ousting the UNFCCC obligations through lex posterior or lex specialis (para 187-195).

This position has significant implications for how the different obligations under the UNFCCC and the Paris Agreement interplay. In this context, it is interesting to discuss how the court has dealt with the interpretation of the principle of common but differentiated responsibilities and respective capabilities, in light of different national circumstances (CBDR-RC-NC) in Art. 2 of the Paris Agreement. There has been a debate on how the Paris Agreement’s CBDR-RC-NC approach, with its focus on a more nuanced self-differentiation, affects the annexe-based CBDR-RC model of the UNFCCC (see Voigt and Ferreira, 2016). However, this decision makes it clear that the Paris Agreement formulation does not change the core meaning of the principle, and rather just recognizes that the developing-developed status is not static (para 226). Some judges, in their separate opinions, have noted the continued relevance of the distinction between developed and developing countries, which is a core part of the structure of climate treaties (See, for e.g. Separate Opinion of Judge Xue, para 65-71; Separate Opinion of Judge Yusuf, para 25-28). The Court has further linked some of these CBDR obligations under the Paris Agreement, such as to provide financial resources, technology transfers and assisting in capacity-building to a broader duty to co-operate, which it has held to be a relevant rule of customary international law (paras 227, 140-142). The Court has further linked CBDR to the duty of due diligence, and has held that the assessment of states’ compliance with various provisions of the Paris Agreement would also factor in their historical contributions, available means and national circumstances (paras 247, 290-292). 

Significantly, the Court has treated the Paris Agreement almost as a living, evolving document. This is apparent from the interpretational approach taken by the Court, which has emphasized “subsequent agreements” through COP decisions, almost as much as the ‘plain text’ of the 2015 treaty. This, for example, is noteworthy in how the Court has interpreted Article 2(1) goal of limiting the global temperature increase to “well below 2℃ above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels”. The Court has interpreted this provision, along with subsequent COP decisions, to hold that 1.5°C is the legally relevant threshold (paras 224-225).

Similarly, the Court has rejected, or at least added more nuance, to the oft-made distinction between obligations of conduct and obligations of result in the Paris Agreement. Noting that this distinction is not a strict one, and some obligations may exhibit the characteristics of both (paras 175, 207), the court specifically noted that the obligations of conduct and result in the Paris Agreement are mutually supportive (para 228). The obligations of conduct under the Paris Agreement, were held to be connected with the customary international law obligation of due diligence (para 135, 228), and that the compliance with those provisions would be assessed on the basis of whether the party “exercised due diligence and employed best efforts by using all the means at its disposal in the performance of that obligation” (para 229). In more concrete terms, it means that the Court has limited the discretion seemingly available to the states in many areas. For instance, the Court has noted that merely preparing, communicating and maintaining nationally determined contributions (NDCs) is not sufficient to comply with Article 4, and the content of the NDCs is equally important (para 236-240).

The Court noted that while the treaty is silent on the content of the NDCs, it does not give parties ‘unfettered discretion’ in preparing NDCs; rather, they are required to ensure that the NDCs reflect their respective highest possible ambition (paras 241-249). By linking the customary international law duty to prevent significant harm to the environment, the court noted that each state’s NDC must be “capable of making an adequate contribution” toward the temperature goal (para 242).

Significantly, the Court recognized the possibility of reviewing the content of the NDCs, by linking it to the duty of due diligence and CBDR. It noted that the standard adopted for assessing NDCs would vary, depending on factors like historical contribution and current levels of development (para 247). Similarly, regarding the obligation of conduct to “pursue domestic mitigation measures” to achieve the NDCs, under Article 4.2, the Court required that the states must take “proactive and pursue measures that are reasonably capable of achieving the NDCs set by them” (para 253). The Court has further clarified that due to the urgency of the deteriorating climate, states will have to meet a stringent due diligence standard to show compliance with this mitigation obligation.

In the context of the provisions on adaptation, the court’s discussion has been relatively limited, though it has again highlighted that the standard of due diligence must be used to assess compliance of states with adaptation obligations (para 258) and that the states must take appropriate steps to enhance adaptive capacity and reduce vulnerability to climate change. 

Finally, the court has also briefly discussed the cooperation obligations in the Paris Agreement, including the financial assistance, technology transfer and capacity building. As regards the financial assistance obligations, the Court reiterated that while the specific amounts are not specified, it must be interpreted along with the overall temperature goals, and factors like the capacity of the developed countries and the needs of the developing countries (para 265).

Some Omissions and Limitations

The Court’s discussion of the obligation of states under the Paris Agreement is progressive and, in many ways, strengthens the operation of these provisions. However, there are some limitations and omissions that are noteworthy. For example, the Court side-stepped the arguments on the specific content of the obligations to cooperate, particularly the climate finance obligations on developed countries, by noting that “(s)tates are free to select the means of co-operating, as long as such means are consistent with the obligations of good faith and due diligence” (para 262). Similar to how the Court used subsequent COP decisions and the global stocktake to strengthen the mitigation-related obligations, as noted before, it could have also referred to subsequent COP decisions on climate finance, including the New Collective Quantified Goal, to more specifically elaborate on these obligations. Instead, the Court chose to simply reiterate the provisions without adding much specificity. 

Similarly, while the Court has linked the Paris Agreement provisions with rules of customary international law, including the duty to prevent harm, the duty to cooperate, and due diligence, it has not made any references to human rights standards being relevant in assessing compliance with the Paris Agreement provisions, although it has discussed several human rights treaties separately. Judge Aurescu, in his separate opinion, has expressed disappointment that the Court has been excessively cautious in dealing with human rights, and regretted that the Court did not expressly hold that the right to a clean, healthy and sustainable environment was part of customary international law (Separate Opinion of Judge Aurescu, para 28, 46). Similarly, Judge Charlesworth discussed the need to also apply the human rights standards, particularly regarding vulnerable groups (Separate Opinion of Judge Charlesworth, para 29). She noted that applying human rights law to climate change obligations would have significant procedural implications, like giving access and standing to people who may not directly be able to enforce climate-related obligations internationally (Separate Opinion of Judge Charlesworth, para 12).

The Court could have clarified that, in addition to due diligence standards, the human rights norms, in terms of the obligation to ‘fulfil’, as a part of customary international law, would also be a relevant benchmark in assessing the compliance of several mitigation and adaptation provisions.

Overall, although this advisory opinion arguably could have gone further and outlined the obligations in more concrete terms, there is reason to be cautiously optimistic about it as it can significantly aid some of the ongoing strategic climate litigations. 

(Rahul Mohanty is an Assistant Professor at the Jindal Global Law School.)