In Between the Lines

Less than a year since the International Court of Justice (ICJ) delivered its Advisory Opinion on Obligations of States in Respect to Climate Change (Advisory Opinion), its wider implications for a range of international law debates is evident (e.g. implications for obligations erga omnes, right to life, state responsibility). This post suggests that the Advisory Opinion is also pertinent to the debate on the conceptual relationship between ‘breach’ and ‘non-compliance’. Although legal scholarship largely converges on the view that a coherent distinction between ‘breach’ and ‘non-compliance’ is difficult to sustain, that distinction has nonetheless been invoked to interpret Article 15 of the Paris Agreement as lex specialis to the general rules on state responsibility. The Opinion, however, aligns with the long-standing view that non-compliance and breach are not fundamentally different concepts but rather characterize the same conduct for which different legal consequences might follow depending on the forum seized.

The Prevailing Consensus and Its Contestation Before the ICJ

The proliferation of compliance mechanism under multilateral environmental treaties (MEAs), alongside international courts and tribunals, has prompted a debate whether these two fora are designed to address different types of internationally wrongful acts––namely, breach and non-compliance (here, here and here). Over times, a broad consensus has emerged in international law scholarship that breach and non-compliance constitute essentially the same conduct, or at least that any meaningful distinction between them is difficult to sustain (see for example here, here and here). Thus, subsequent scholarship has increasingly focused on procedural intricacies and the legal character of the outcomes produced by the compliance mechanisms, often in juxtaposition with the corresponding features of international adjudication (here and here). Amidst this consensus, the alleged ‘fundamental difference’ between the concepts of breach and non-compliance was still invoked in relation to the Paris Agreement’s Article 15 provisions on the implementation and compliance mechanism (establishing the Paris Agreement Implementation and Compliance Committee ‘PAICC’). In their written statements, States argued that the compliance mechanism envisaged by Article 15 provisions either take precedence over, or potentially supplant the general rules on state responsibility as lex specialis.

States arguing for PAICC process taking precedent (e.g. China, Iran, Kuwait, Saudi Arabia, European Union and Organization of Petroleum Exporting Countries ) saw in the latter a process that is better suited to account for the goals of the Paris Agreement, disparities in state capabilities, the drawbacks of long-lasting litigations, and largely conduct-based nature of Paris obligations. Those in the opposite camp, suggested that the two processes are distinct and not replaceable, invoking non-adversarial nature of the PAICC, absence of express reference to state responsibility in Article 15, as well as non-punitive, non-adjudicative consequence of non-compliance decision-making (e.g. Dominican Republic, Antigua and Barbuda, Bahamas, Sri Lanka, and Vanuatu). In the latter context, Vanuatu further relied on the reasoning of the International Law Commission’s Special Rapporteur on the Protection of the Atmosphere, Shinya Murase, purporting an alleged “fundamental difference” between “breach” and “non-compliance”. According to this reasoning, the distinction between the two is that a breach entails international responsibility on an objective conception of the underlying incident, whereas non-compliance gives rise to amicable solutions that take into account subjective factors, such as the technical or financial difficulties faced by States (here).

Breach and Non-Compliance in the Advisory Opinions

The response of the Court to the lex specialis argument is essentially negative. It reaffirms the long-standing scholarly consensus by observing that the PAICC does not have the power to settle disputes or provide remedies. Nor does it have the capacity to determine state responsibility. In reaching this conclusion, however, the Court makes no reference to any purported ‘fundamental difference’ between the breach and non-compliance. Its arguments rest solely on three institutional-functional features of the PAICC enshrined in Article 15 provisions: transparency, non-adversarialism and non-punitiveness (Advisory Opinion, paragraph 416).

Instead, the Court’s treatment of these concepts of breach and non-compliance throughout the Advisory Opinion points to their interchangeability rather than to any fundamental difference. At paragraph 416, the Court definitively concluded that “responsibility for breaches of the obligations referred to in question (a) [is] to be determined by applying the rules on State responsibility under customary international law”. Yet throughout its analysis, the Court uses the terms “breach”, “non-compliance”, and “failure to comply” interchangeably when describing the same conduct. For instance, when discussing the Paris Agreement, the Court states that “compliance of parties with obligations of conduct [is] to be assessed on basis of whether party in question exercised due diligence” while simultaneously characterizing inadequate action as constituting “internationally wrongful acts” attracting state responsibility. The Court further observed that “the internationally wrongful act in question is not the emission of GHGs per se” but rather “the breach of the obligations” causing significant harm. This formulation treats breach and non-compliance as describing the same underlying conduct—the failure to fulfil climate obligations.

Crucially, in paragraph 427, the Court stated that “failure of a State to take appropriate action to protect the climate system from [greenhouse gas] emissions […] may constitute an internationally wrongful act which is attributable to that State”. Here, the term ‘failure’ (often associated with non-compliance) is equated with the commission of an ‘internationally wrongful act’ (the language of breach and the law of state responsibility). Moreover, in paragraph 221 the Court concludes that “non-compliance with emission reduction commitments by a State may constitute an internationally wrongful act”. As regards to the latter, the mandate of the PAICC comprises consideration of non-compliance of Parties in relation to emission reduction commitments, including non-communication or non-maintenance of nationally determined contribution under Article 4 of the Paris Agreement (Decision 20/CMA.1). This terminological conflation throughout the Court’s advisory opinion suggests the view that the same conduct may properly be characterized as both non-compliance and breach depending on the institutional context.

The treatment of breach and non-compliance as synonyms finds further support in the advisory opinions rendered by International Tribunal of the Law of the Sea (ITLOS) and the Inter-American Court of Human Rights (IACtHR), both of which similarly collapse any purported distinction between these concepts in the climate change context. The ITLOS Advisory Opinion on Climate Change and International Law, delivered in May 2024, explicitly acknowledged that states have “stringent” due diligence obligations under UNCLOS to prevent, reduce, and control marine pollution from anthropogenic GHG emissions, and emphasized the potential for liability arising from “breach” of or “failure to comply” with these obligations—using both terms to describe the same conduct. Moreover, ITLOS found that due diligence encompasses both enactment and enforcement of laws regulating GHG emissions, characterizing inadequate action as both “non-compliance” and conduct engaging “international responsibility” (paragraphs 145-47). Similarly, the IACtHR, in its Advisory Opinion on the Climate Emergency and Human Rights delivered in January 2025, employed breach and compliance terminology interchangeably when describing state failures to meet climate obligations, emphasizing that such failures trigger human rights responsibilities under the American Convention’s Article 11 (paragraphs 246, 302-304).

Discussion

Across all three advisory opinions, the pattern is consistent: international courts and tribunals treat breach and non-compliance as characterizations of the same underlying conduct. Thus, the failure to fulfil international obligations. The tribunals emphasize that what matters is whether states have exercised due diligence in meeting their obligations and whether that assessment occurs through compliance mechanisms or adjudicatory proceedings. This convergence challenges any claim that breach and non-compliance represent fundamentally different categories of state conduct requiring distinct conceptual treatment.

The ICJ’s emphasis on the three institutional features of the PAICC––transparency, non-adversarialism, and non-punitiveness––further illuminates this point. These features describe the procedural character and institutional design of the compliance mechanism, not the nature of the conduct. A state’s failure to meet its Paris Agreement obligations remains the same conduct regardless of whether it is managed by the PAICC through facilitative dialogue or is judicially determined to constitute a breach triggering state responsibility. The difference lies in the forum’s mandate and the legal consequences that forum is empowered to prescribe, not in the conduct itself. The PAICC manages non-compliance through facilitative, transparent, non-adversarial, and non-punitive procedures, while courts apply state responsibility rules, determine breaches and prescribe legal consequences including cessation, guarantees of non-repetition, and full reparation. Yet, both address the same conduct: state failures to fulfil climate obligations.

Conclusion

The ICJ’s Advisory Opinion contributes to the longstanding debate on the relationship between breach and non-compliance in international environmental law. By using these terms interchangeably throughout its analysis and by grounding its response on procedural and institutional features (lex specialis) rather than substantive differences in conduct, the Court affirms that breach and non-compliance are not fundamentally distinct concepts. Rather, they are essentially applied to name the same conduct.

This conclusion finds support in the parallel advisory opinions of both ITLOS and the IACtHR, which similarly treat compliance failures and breaches as equivalent when addressing climate-related obligations. The convergence across these tribunals suggests an emerging consensus that under most of the MEAs whether an internationally wrongful act results in management of non-compliance or determination of responsibility depends largely on the forum seized. Specifically, whether that forum is a compliance committee with a facilitative mandate or an adjudicatory body with authority to determine legal consequences under the rules of state responsibility. Both address the same underlying conduct but serve different functions within the international legal order—one facilitative and forward-looking, the other determinative and concerned with legal consequences. This clarity has important implications for the future development of international environmental law: Affirming that states cannot shield themselves from judicial review by pointing to the existence of non-compliance mechanisms, while simultaneously preserving space for facilitative approaches that may prove more effective in promoting behavioural change. The Advisory Opinion thus strengthens both pathways for addressing climate obligations, recognizing them as mutually reinforcing rather than mutually exclusive approaches to ensuring state compliance with the urgent imperatives of climate action.