Revolution or Status Quo? The ICJ Dilemma in Defining States’ Climate Obligations

[Erard de Schaetzen is pursuing a masters in public international law at Utrecht University]

In March 2023, Vanuatu’s initiative led the UN General Assembly to adopt a Resolution requesting an advisory opinion from the International Court of Justice (ICJ) on defining States’ obligations regarding climate change, and the legal consequences arising from their breach. Since then, proceedings before the “World Court” have received unprecedented global attention, with 91 written statements from States and international organizations, followed by even more oral statements in December 2024. At first sight, such widespread engagement reflects the recognition of climate change as a global challenge in which most States seek a legal voice. Yet, a closer examination of the submissions reveals a deep and enduring divide between powerful wealthy countries and vulnerable developing States. This divide highlights a fundamental question: why is the content of climate obligations so controverted and arduous to define?

Generally speaking, States’ obligations under international law derive from two main sources: treaties and custom. Hence, international law is either born out of freely stipulated conventions between nations, or emerges from consistent and general State practice widely accepted as law. Newcomers to the field might be tempted to view treaties as the righteous product of mutual consent, crafted through rigorous negotiations between equal sovereigns who freely determine their future commitments; while perceiving customary law as a form of “tyranny of the majority,” where the mass of the international community imposes obligations on all States regardless of their individual preferences. 

However, the ongoing ICJ proceedings reveal that international law dynamics are far more ambiguous. This post examines how wealthy States, exploiting global climate inequalities, have shaped treaties to their advantage and are now invoking these frameworks to steer the Court toward preserving this status quo. It further discusses how developing nations are mobilizing customary law as an alternative path toward climate justice, urging the Court to affirm the broader, more robust, and more equitable nature of customary climate obligations. Ultimately, the ICJ’s forthcoming opinion must confront this tension to define the actual scope of international climate responsibility.

How Global Inequalities Shape Climate Change Conventional Law

Climate change is undeniably haunted by profound inequalities. While the world’s poorest countries contribute the least to global anthropogenic emissions, they are disproportionately vulnerable to its devastating consequences, including extreme weather events such as floods, heatwaves, and drought. Conversely, industrialized nations, particularly those in the Global North, bear the greatest historical responsibility for CO₂ emissions, yet they remain relatively insulated from the most severe climate-related harms.

This asymmetry is denounced in environmental agreements negotiations, where less developed countries and small island nations typically demand immediate action from post-industrialized and emerging economies. Meanwhile, developing nations in Latin America, Asia, and Africa invoke the historical “environmental debt” of post-industrialized States, exhorting them to bear the principal burden of mitigation efforts and provide financial, technological, and logistical support to help developing countries’ adaption. Concurrently, they assert their right to economic development. These concerns are legally translated into the principle of common but differentiated responsibilities (CBDR). Moreover, they shape how the two main climate strategies, mitigation and adaptation, are addressed. Mitigation is predominantly understood as a developed nation’s responsibility, requiring them to minimize GHG emissions, while adaptation is viewed as a priority for developing countries facing deleterious climate impacts.

In practice, however, post-industrial States largely define the global agenda, and green finance overwhelmingly favors mitigation over adaptation. Most private and State-backed funding goes to mitigation, mainly as loans directed to high-productivity Asian countries for promising investment returns. Conversely, adaptation projects, despite their vital importance for endangered communities, attract way less funding due to lower financial incentives and limited investor appeal, deepening global climate injustice. Furthermore, inequalities between industrialized and developing nations are embedded in the very elaboration of international environmental treaty law. When the three climate treaties (UNFCCC, Kyoto Protocol and Paris Agreement) were negotiated, it was less States’ “free consent” than power dynamics that played a decisive role in their scope. Differing capabilities in climate negotiations advantage wealthy countries, obtaining low-income States’ consent by promising material and institutional support, notably via green finance. Additionally, Global North countries are generally better equipped to deploy large delegations with expert advisors to navigate the negotiations’ technical intricacies. In contrast, Global South nations, sometimes lacking individual negotiators, routinely negotiate in groups (e.g., AOSIS, G77), occasionally even relying on western advisors. Disparities in diplomatic resources, agenda setting, and leverage are ultimately detrimental to vulnerable States, undermining negotiation fairness and agreement equity. Consequently, environmental treaty law risks entrenching the preferences of powerful parties and the existing status quo, echoing Pascal’s quote, “Unable to make what is just strong, we have made what is strong just”.

Conversely, customary international law may offer developing countries a more favorable legal framework for climate action, as they form the majority of the international community. Relevant principles could include the duty of due diligence, the principle of prevention, the no-harm rule, the precautionary principle, international human rights and UNCLOS. However, custom is not only shaped through widespread State practice, but also requires opinio juris (the belief that such practice is legally obligatory). As the ICJ notoriously ruled, “not only must the acts concerned amount to a settled practice, but they must also be such, or be carried out in such a way, as to be evidence of a belief that this practice is rendered obligatory by the existence of a rule of law requiring it.” Hence, challenges arise in establishing whether such customary principles extend to cover anthropogenic GHG emissions.

One Opinion, Two Claims

Given the striking North-South inequalities, and how States weaponize conventional or customary law to advance opposing interests, tasking the ICJ to render an opinion on climate obligations and their legal consequences puts it in quite a delicate position. It is almost as if the Court were settling a dispute – quite paradoxical, since advisory opinions are not considered “decisions” under Article 59 of the ICJ Statute. They are non-binding, involve no formal parties, and merely “reply” to legal questions. Unlike contentious cases, where non-compliance can be referred to the UN Security Council under Article 94 of the UN Charter, advisory opinions lack any enforcement mechanism. Yet, they still carry legal consequences, as the International Law Commission classifies them as “judicial decisions” under Art. 38(1)(d) of the ICJ Statute, granting them authoritative influence over international law’s interpretation around the globe.

Regarding States’ climate obligations, the ICJ faces two main legal avenues, illustrated in the written submissions of the participants to the proceedings:

The minority position, championed by post-industrialized and emerging States, favors a treaty-limited scope of appreciation. They argue that the climate treaty regime constitutes “the most directly relevant applicable law”, functioning as “lex specialis” overriding any conflicting customary rule or broader principles of international law. This is unsurprising, as the three climate treaties primarily rely on bottom-up processes and political commitments rather than strict legal duties. For instance, under Article 4(2) of the Paris Agreement, States must prepare, communicate, and maintain Nationally Determined Contributions, but this obligation is procedural: States determine freely their commitments and are not legally bound to achieve them. Consequently, this interpretation rejects the application of customary international law, including the due diligence and prevention principle. The UK, for example, has argued that the customary obligation to prevent significant transboundary environmental harm does not extend to GHG emissions, as this principle traditionally applies in a bilateral, non-global context, requires specific attribution to a single State, and protects the environment of particular States rather than the “climate system” as a whole. Similarly, this position holds that principles such as CBDR, intergenerational equity, the polluter-pays principle, and the precautionary principle, are not freestanding custom but must instead be interpreted strictly within the specific instruments incorporating them. Likewise, should human rights obligations be recognized in this context, they should be understood as future-oriented, procedural duties focused on mitigation.

Concerning State responsibility for internationally wrongful acts, these States contend that secondary rules of responsibility must also be assessed within the treaty framework. This suggests several legal consequences: some States assert that the Paris Agreement’s non-judicial ‘Loss and Damage’ mechanism supersedes customary State responsibility rules; others argue that responsibility cannot be invoked for acts predating the 1992 UNFCCC’s adoption; and others claim that complexities of causation and attribution of anthropogenic emissions make it impossible to establish specific State responsibility for climate-related harm.

Alternatively, the custom-oriented perspective of developing countries regards the climate treaty regime as just one part of a broader legal corpus also encompassing human rights, self-determination, and marine environmental protection. Central to this approach is the application of customary principles, particularly the due diligence duty and the prevention principle, to GHG emissions. These principles, previously consecrated in the ICJ Corfu Channel Case and Nuclear Weapons Opinion, mandate States to prevent significant transboundary harm caused by activities within their jurisdiction and control. Recognizing these principles in the climate context would extend this duty beyond protecting other States’ environments or areas outside national jurisdiction – to safeguarding the entire climate system. Furthermore, States like Vanuatu advocate for the inclusion of a duty to protect and preserve the marine environment, referencing ITLOS’ advisory opinion on UNCLOS’ applicability to climate change. They also support positive human rights obligations under the UDHR, mandating that States implement sufficient measures to combat climate change and safeguard individuals from its adverse effects. The jurisprudence of regional courts, such as the European and Inter-American Courts of Human Rights, and UN treaty bodies, such as the Human Rights Committee, could inform the ICJ’s findings.

Regarding legal consequences, these States largely agree that when a State’s actions or omissions contribute to climate harm, general customary rules of State responsibility apply – entailing both cessation of wrongful conduct and full reparation. It is further argued that, pursuant to these rules, certain obligations are owed erga omnes, i.e. to the international community as a whole. This includes obligations arising from basic human rights, as previously recognized by the ICJ, the protection of which all States have a legal interest in, regardless of direct injury, and thus hold standing for invoking the violating State’s international responsibility. Likewise, the prevention principle is also considered an erga omnes obligation, due to the ubiquitous nature of the climate system, forming part of the shared environment of all States. Accordingly, any State could claim a legal interest in holding a major GHG-emitting State accountable for breaching its due diligence obligation and causing harm beyond its national jurisdiction.

Conclusion: The International Court’s Dilemma

In the upcoming months, the Court will be facing quite a dilemma. A narrow, treaty-based approach would crystalize the status quo and its power imbalances, preserving a system where wealthy States may retain GHG-intensive production and consumption models whereas their legal accountability remains minimal. Relying solely on the UNFCCC and Paris Agreement’s lenient provisions would favor these States, as no binding international norm would constrain their climate policies – only vague programmatic pledges allowing relatively wide discretion. Beyond the general duty under international law to apply treaties in good faith, it is difficult to imagine how any State or civil society member could challenge a government’s climate inaction when legal standards are so vague and self-defined. Such interpretation would allow major emitters to continue their carbon-heavy economic models, while formally appearing to comply with international law through weak domestic legislation that avoids any real disruption.

Conversely, a broader custom-based interpretation would reinforce the rule of law, pressuring States toward carbon neutrality under the weight of legal responsibility. The ICJ would thereby align with the jurisprudence of regional and international human rights bodies and courts, fostering interpretive coherence on State responsibility in the climate context. Grounding its opinion in binding customary norms – such as the prevention principle or positive obligations to protect human rights extraterritorially – would make climate obligations legally opposable. These would not be vague policy commitments defined unilaterally, but legal obligations owed erga omnes. Sure, it would not erase global inequalities overnight, as a gap often exists between norms and their actual implementation. Still, it would re-equilibrate the scales, giving vulnerable countries and communities a legal foothold to demand accountability from the biggest polluters. It would also send a symbolic message: that entrenched power structures causing climate harm aren’t just unjust – they’re unlawful.

That said, because its sociopolitical legitimacy depends heavily on State support, the ICJ will likely proceed cautiously. Departing from the status quo risks alienating powerful States which, if antagonized, may undermine the Court’s authority by disengaging from future proceedings, much like the United States and France did when they withdrew from the ICJ’s optional clause following unfavorable rulings in the Nuclear Tests and Nicaragua cases. Conversely, a refusal to go beyond treaty law may produce similar retaliation from Global South States. The outcome of the South West Africa cases, for instance, prompted freshly decolonized nations to view the ICJ as a relic of colonial power and to turn away. Hence, fears of political backlash may tempt the court to find a middle ground, and to render a Solomonic judgment. One way or another, this advisory opinion will shape the future of climate law – and it is safe to bet the conversation will not end once its ruling is handed down.

Photo attribution: Composite design by Erard de Schaetzen, based on freely available online images