The ICJ Advisory Opinion on Climate Change: December 2024 Hearings
By Eugenia Recio, Post-doctoral Researcher
Keywords: climate change, International Court of Justice, Nationally Determined Contributions, advisory opinion, state responsibility.
Photo by Rafael Ishkhanyan on Unsplash
The International Court of Justice (ICJ) is set to play a significant role in the legal response to climate change. The United Nations General Assembly (UNGA) resolution spearheaded by Vanuatu and supported by over 100 countries, requested the ICJ to provide an advisory opinion on two pressing questions:
- What are the obligations of States under international law to ensure the protection of the climate system from anthropogenic greenhouse gas (GHG) emissions for States and future generations?
- What are the legal consequences under these obligations for States that, through their acts or omissions, have caused significant harm to the climate system with respect to States and peoples from present and future generations?
The ICJ hearings on these proceedings took place from 2 to 13 December 2024, standing out for being one of the most comprehensive advisory opinion processes in the ICJ’s history. The oral hearings offered 96 States and 11 international organizations the opportunity to present their perspectives and expand on their written submissions. This overwhelming record of engagement underscores the urgency and significance of climate change as a legal challenge. This post highlights key issues debated.[1]
- Clarifying climate-related obligations
A primary issue discussed at the hearings involved identifying the diverse sources of international law relevant to climate change. According to Article 38 of the ICJ Statute, sources of international law include existing treaties, principles of international law, customary international law and judicial decisions.
1.1 Climate treaties
The international climate agreements—particularly the UN Framework Convention on Climate Change (UNFCCC, 1992) and the Paris Agreement (2015) — were widely recognized as the starting point for identifying States’ obligations to protect the climate system. However, the content and legal nature of Paris Agreement’s obligations were intensely debated, particularly those to submit Nationally Determined Contributions (NDCs) with an expectation to reflect States’ ‘highest possible ambition’ (Article 4). The role of science, especially of the Intergovernmental Panel on Climate Change (IPCC) in informing the content of obligations has been widely recognized, particularly in light of current NDCs that would lead to a scenario increase of 2.7C temperature by 2100.
Noting that the law should support a strengthened response to climate change, many countries stressed the requirement for nations to align their NDCs with the Paris Agreement’s temperature goal of limiting global temperature rise to well below 2°C while pursuing efforts to cap it at 1.5°C above pre-industrial levels (Article 2.1) (COSIS in CR 2024/53, Cote d’Ivoire in CR 2024/39, IUCN in CR 2024/54). In particular, some countries, such as Antigua and Barbuda, specified that each NDC must be set to a level corresponding with the remaining carbon budget to achieve the Paris Agreement 1.5ºC goal (CR 2024/36). On the opposite end of the spectrum, oil-producing and high-emitting countries stated that the Paris Agreement’s temperature goal is merely aspirational (Saudi Arabia in CR 2024/36, the US in CR 2024/40). Moreover, the lack of standards or mechanisms internationally agreed to apportioning fair shares of the remaining global carbon budget was mentioned by some (the EU in CR 2024/54, the US in CR 2024/40, Switzerland in CR 2024/50), noting the diversity and controversy around metrics to set fair shares.
In addition to discussing mitigation obligations, developing countries highlighted obligations related to financial provision, technology transfer and capacity building, which are, according to them, manifestations of the principle of international cooperation embedded in the climate regime (India in CR 2024/42, Bolivia in CR 2024/36, Bangladesh in CR 2024/36, Saint Lucia in CR 2024/48). The principle of common but differentiated responsibilities and respective capabilities (CBDR-RC) was invoked, with many developing countries emphasizing that climate-related duties do not compel them to act without regard to their development needs. However, the content and implications of this principle remain highly controversial. Oil-producing countries invoked the principle to highlight differentiated obligations in the climate treaties and to consider varying historical emissions and current capabilities (Saudi Arabia in CR 2024/36). Others, such as Ecuador, view the principle as an equalizer that corrects the disproportionate burden on States that have not contributed, or have only marginally contributed, to climate change (CR 2024/40, African Union in CR 2024/44). A number of developed countries cautioned that the CBDR-RC principle is dynamic, not static and cannot be used by countries—particularly developing (high-emitting) countries—as a pretext to avoid responsibility for climate action (Nordic countries in CR 2024/39, Switzerland in CR 2024/50, France in CR 2024/41). Yet, others, such as the US, disregarded CBDR-RC as an overarching principle of the Paris Agreement (CR 2024/40).
1.2 Principles of international law and customary international law
Beyond obligations emerging from the climate treaties, the role of customary international law was debated. The customary no-harm principle establishes States’ obligations to ensure that activities undertaken within their territories do not cause transboundary environmental harm to third countries. The principle has been invoked in previous judicial cases of environmental harm in the context of transboundary rivers and air pollution (Pulp Mills on the River Uruguay case, Gabčíkovo-Nagymaros Project case, Trail Smelter arbitration case), particularly when damage is traced to one, often neighboring, State.
Citing that the UNFCCC preamble refers to this principle, many vulnerable and developing countries argued that current best available science by the IPCC provides a sufficient basis to establish a general causal link between GHG emissions, climate change and climate-induced harm (Belize in CR 2024/37, COSIS in CR 2024/53). In contrast, other countries, such as Australia (CR 2024/36) and UK (CR 2024/48) rejected the application of this principle, arguing that GHG emissions lack the direct causation and proximate temporal effects typical of transboundary harm case law.
The due diligence duty that derives from the no-harm principle requires that States assess potential foreseeable risks of activities undertaken in their territory before they materialize, as well as carry out environmental impact assessments, cooperate with and notify potentially affected States of such risks. Accordingly, the due diligence obligation of preventing significant transboundary harm arises when a State can reasonably foresee the risk of significant harm and the causal link between its activities and the potential harm. In this context, Barbados cited evidence that countries such as the US, the UK, France, West Germany, and the Union of Soviet Socialist Republics, knew at least since the 1960s that extensive use of fossil fuels would lead to “drought, famine, and political unrest” but continued with their actions, breaching obligations of due diligence (CR 2024/36). Yet, others, such as Switzerland, argued that it is only since 1990 when the first IPCC report provided scientific evidence of such relationship concluding that anthropogenic emissions “could lead to irreversible climate change” (CR 2024/50).
Accepting that the no-harm principle is a source of climate-related obligations could have significant implications in establishing since when a State could be held responsible for failing to comply with its obligations to prevent climate-induced harm. At the same time, Switzerland suggested that the polluter-pays principle offers a more appropriate framework for addressing climate change by ensuring that those responsible for pollution bear the costs of managing it. It further noted that western industrialized countries, as of 2023, represent only three of the ten largest emitters (ibid).
1.3 Clarifying human rights obligations in climate law
Whether human rights law is a source of climate-related obligations alongside climate treaties was a prominent topic of discussion. Many States pointed to the Paris Agreement’s preamble, which recognizes the link between climate action and human rights (Albania in CR 2024/35, Saint Lucia in CR 2024/48). The European Court of Human Rights’ Klimaseniorinnen case was referred by some to argue that climate change is a common concern of humankind and that merely developing NDCs does not automatically satisfy the requirements of human rights law (e.g. Chile in CR 2024/38).
Here, the debate centered on the various human rights dependent on and affected by climate change impacts. Special attention was given to the right to a healthy environment, which has been recognized in, among others, the Inter-American Court of Human Rights’ 2017 Advisory Opinion and UNGA Resolution 76/300 on the human right to a clean, healthy and sustainable environment. This recognition could mean acknowledging that States have obligations to: prevent significant harm to the climate system that violates human rights; ensure that climate measures do not infringe on human rights; and provide redress for human rights violations resulting from climate change impacts (Albania in CR 2024/35).
Some States, however, rejected the applicability of human rights law to climate change (Germany in CR 2024/35 and Canada in CR 2024/38), explaining that human rights treaties aim to protect individuals from concrete violations within the jurisdiction of the State. To counter these arguments, some States invoked General Comment Nº 26 from the UN Committee on the Rights of the Child, which extended human rights obligations to transboundary harm, considering that when transboundary harm occurs, children are under the jurisdiction of the State in whose territory the emissions originated (e.g. Portugal in CR 2024/48). States arguing against broadening the scope of human rights law cautioned that extraterritorial application could only apply to jus cogens norms, not universal duties to reduce GHG emissions (Germany in CR 2024/35 and Canada in CR 2024/38). Vulnerable States counterargued that climate-related displacement threatens their right to self-determination, a peremptory jus cogens norm from which no derogation is permitted and which is binding on all States with an extraterritorial application (Fiji in CR 2024/40, Micronesia in CR 2024/45, Saint Vincent in CR 2024/49). Others added that human rights law presumes that States are the primary guarantors of rights, a presumption that collapses when GHG emissions from third countries threaten their existence, leaving States unable to protect individuals within their jurisdiction from climate-related human rights violations (Kiribati in CR 2024/43).
1.4 Interplay between different sources of climate obligations
To describe the relationship between the climate treaties and broader international law principles, particularly those under customary international law and international human rights law, some countries cited the doctrine of lex specialis (China in CR 2024/38 and South Korea in CR 2024/38). Those arguing that only the climate regime provides the obligations related to climate change said that according to this well-established doctrine more specific rules take precedence over general standards. However, a significant number of participants dismissed this view, arguing that compliance with the Paris Agreement is essential but does not eliminate coexisting State obligations under customary law and human rights treaties (e.g. Antigua and Barbuda in CR 2024/36). Moreover, many stressed that the application of the lex specialis doctrine is relevant only in the context of conflict among norms, which is not typically the case for climate-related obligations.
In this regard, many also pointed to the Vienna Convention on the Law of Treaties (VCLT) and its provisions concerning harmonious interpretation and systemic integration, particularly under Article 31, which stipulates that treaties should be interpreted in good faith in accordance with the ordinary meaning of their terms, in their context, and in light of their object and purpose. When obligations arise from different treaties, this guides their reconciliation through a harmonious interpretation that reflects the overall intent of the parties. Therefore, this approach would allow for the reconciliation of the Paris Agreement’s commitments with other climate-related obligations. Some countries argued that harmonious interpretation of obligations does not mean incorporating obligations from other treaties or customary law into the climate treaties (Australia in CR 2024/36). The EU emphasized that the coexisting State obligations under climate change, human rights, environmental and maritime law regimes mutually inform one another but cannot alter the nature of these obligations (CR 2024/54). Others, such as Saint Lucia, stated that the principles of systemic integration and harmonious interpretation allow for autonomous application of the obligations (CR 2024/48).
Thus, this raises a critical question for the Court: how would the principles of harmonious interpretation and systemic integration operate in the concrete case of climate change obligations? Among diverse proposals, Seychelles said that any conduct contrary to the Paris Agreement’s goals constitutes a breach of the customary no-harm obligation and that the requirement for States to make their ‘best efforts’ to comply with the Paris Agreement is an obligation of conduct, which should be assessed against the due diligence standard (Seychelles in CR 2024/49).
2. Legal consequences for breaching climate obligations
A second issue discussed during the hearings pertained to the legal consequences for States that breach their climate obligations, considering the harm caused to the climate, the environment, vulnerable States, and both present and future generations.
Developed and developing high-emitting States highlighted the non-punitive and collaborative compliance mechanisms designed under the climate treaties. They argued that these mechanisms were specifically established to address the legal consequences for States that have caused significant harm to the climate system (China and Canada in CR 2024/38).
Countering arguments that climate treaties constitute a self-contained regime, many participants referred to the applicability of customary rules codified in 2001 by the ILC in its Articles on the Responsibility of States for Internationally Wrongful Acts (ARSIWA). According to ARSIWA, State responsibility arises from a “wrongful act” attributed to a State in breach of an international obligation (Article 2). This breach occurs when a State fails to act in accordance with an obligation set in a treaty, or in customary international law. ARSIWA provides that the State responsible for the wrongful act must cease the act and offer assurances that it will not be repeated (Article 30). The responsible State is also obligated to make full reparation for the injury caused by the wrongful act (Article 31). Three main ways of reparation are recognized:
- Restitution, which means restoring the situation to how it was before the wrongful act.
- Compensation, which refers to providing financial payments for the damage caused.
- Satisfaction, which implies measures to acknowledge the breach, provide moral reparation and prevent future violations.
During the hearings, many developing States supported the applicability of ARSIWA in the climate context and provided examples of actions that could facilitate the diverse forms of reparation due to climate-induced damages. However, a key requirement for establishing responsibility and associated legal consequences is proving a direct link between the wrongful act and the injury. Some developing States argued that for the case of climate change the act of emitting GHG could amount to a ‘composite’ wrongful act under Article 15, resulting from accumulated actions by different States over a long period (e.g. Colombia in CR 2024/38, Egypt in CR 2024/39). Accordingly, responsibility for collective harm should be apportioned based on each country’s contributions to that harm (Chile in CR 2024/38).
Noting that the proceedings are not contentious, COSIS stated that only general, not detailed, findings on attribution are requested from the ICJ and pointed to the sufficiently proven connection between GHG emissions, climate change and the resulting impacts (CR 2024/53). They called on the ICJ to recognize the linkage between harm and emissions. Yet, some States argued that GHG emissions are not a wrongful act (China in CR 2024/38); others that emissions occurring before the creation of specific climate obligations do not constitute internationally wrongful acts (the US in CR 2024/40); and others that assigning specific, quantifiable compensation obligations to individual States under international law is currently impossible due to the absence of an agreed-upon framework for allocating the remaining global emissions budget, making it impossible to distinguish lawful from unlawful emissions (Switzerland in CR 2024/50). The Nordic countries also stressed that all States are injured and responsible at the same time, jeopardizing clear attribution (CR 2024/39).
3. Conclusion
The ICJ deliberations are now underway, and the Court is expected to deliver its advisory opinion in 2025. The hearings highlighted unprecedented challenges that climate change poses for international law. For instance, participants pointed to many existing gaps in international law for addressing emerging issues, including the status of climate migrants and the consequences for statehood of countries that have lost their territory to sea-level rise.
In the face of insufficient action to reverse the catastrophic situation that vulnerable developing States are facing, they called for a robust legal opinion in the hope that it will reinvigorate the climate negotiation process and foster stronger and faster climate action, including within the context of NDCs to be submitted in 2025. This underscores the increasing reliance on international law to address an existential global threat that has so far remained inadequately addressed in ongoing negotiation processes.
All this raises the critical question of whether the ICJ will support international law in its ability to address a global crisis as vast and complex as climate change. The Court’s advisory opinion could play a crucial role in shaping international legal frameworks, supporting ongoing domestic climate litigation efforts and promoting effective climate action worldwide. On the final day of the hearings, the judges posed several questions that may signal an openness to a broader interpretation of climate treaty obligations—one that considers both their objectives and the human right to a healthy environment. However, rooted in traditional concepts and doctrines, it is unlikely that the Court will adopt an overly progressive view on these matters. What is certain is that the ICJ will have a unique opportunity to provide much-needed guidance. As the world watches, the outcome of these deliberations may set a significant precedent for how international law evolves to meet the challenges of the 21st century.
[1] All the verbatim records cited in this post are available at: https://www.icj-cij.org/case/187/oral-proceedings.