Jus Cogens and the Climate Crisis

While there are many aspects of the Inter-American Court of Human Rights (IACtHR)’s Advisory Opinion 32/25 (AO-32/25) that are new and groundbreaking, the inclusion of a reflection on jus cogens might have surprised some observers.

This is the first time that an international court has explicitly recognised the jus cogens character of the obligation not to create irreversible damage to the climate and the global environment.

The majority of the IACtHR concluded that “[b]y virtue of the principle of effectiveness, the peremptory prohibition of anthropogenic conduct that may irreversibly affect the interdependence and vital balance of the common ecosystem that makes life possible for species constitutes a norm of jus cogens.” (para. 8) Notably, however, three of the Judges, including the IACtHR’s current President, dissented from this conclusion.

Jus cogens norms are a special kind of customary law. Customary law is created by States through state practice and corresponding opinio iuris. It is generally binding on all states, with limited exceptions for states that have consistently objected to a particular norm of customary international law. But, within this broad category, there are certain norms that are recognised by the international community of States as a whole and from which no derogation is permissible, even through treaties or agreements. Only those constitute norms of jus cogens. 

The legal consequences of a norm being classed as jus cogens are several in international and domestic law. Any international agreement that violates jus cogens is void ab initio. States cannot disregard these obligations, and violations are violations against the international community as a whole, meaning that all States, not just the injured State, can require compliance. In domestic law, States will normally prohibit the behaviour and use criminal law to reinforce such prohibition. 

This blog argues that while the recognition of a jus cogens norm protecting against existential threats to life on Earth may initially appear expansive or novel, the IACtHR’s conclusion in AO-32/25 rests on solid foundations. While not following the established International Law Commission (ILC) methodology, the IACtHR’s reasoning draws upon the established understanding that jus cogens norms emerge from the most fundamental values of the international community, and the preservation of human existence itself represents the ultimate prerequisite for all other human rights protections. Given the Court’s progressive jurisprudence on environmental rights and the interconnectedness of human rights with ecological integrity, the elevation of protection against planetary-scale threats to jus cogens status reflects a logical evolution of international law’s core commitment to safeguarding against irreversible damage to the climate and the global environment.

Jus Cogens and the Climate Crisis

Although the concept of jus cogens has faced some controversy since its early discussion in legal literature and obiter mention in the International Court of Justice’s (ICJ’s) Barcelona Traction case, it now enjoys widespread acceptance among legal commentators, courts, and tribunals. This consensus is reflected in Article 53 of the Vienna Convention on the Law of Treaties, which establishes that jus cogens norms cannot be derogated by treaty or acquiescence, but only by the emergence of a new jus cogens norm. The international legal community has further solidified this acceptance through the ILC Articles on State Responsibility (ILC Articles) and especially the 2022 ILC Draft Conclusions on Identification and Legal Consequences of Peremptory Norms of General International Law (jus cogens) (ILC Draft Conclusions), which collectively forge an international consensus on the existence of several jus cogens norms. The ICJ has itself recognised specific norms as having jus cogens character, including self-determination, the prohibition of racial discrimination and apartheid, slavery, aggression, and genocide.

While the consequences of a breach of a jus cogens norm are currently being tested in ICJ cases, it is clear that no country should benefit from a breach of a jus cogens norm. It is perhaps this insight, together with a general obligation of States to cooperate to address a violation of jus cogens, that is most relevant when it comes to the obligation not to create irreversible damage to the climate and the global environment.

An Existential Threat violating an Essential Human Value

The IACtHR’s analysis in AO-32/25 highlights the international community’s growing commitment to developing legal frameworks that protect essential human values and ensure planetary habitability for current and future generations. International environmental law has established key principles like precaution and polluter pays, created erga omnes obligations to prevent transboundary harm, produced agreements addressing climate change and biodiversity loss, developed concepts of intergenerational equity, and pursued criminalisation of conduct causing severe environmental damage. These developments highlight, in the eyes of the IACtHR, that the obligation not to create irreversible damage to the climate and the global environment cannot be treated like any other obligation. The fact that the prohibited conduct creates “risks of irreversible damage to the ecosystems that sustain life” (para. 287) is another important indicator for the IACtHR of the jus cogens character of the norm.  

The IACtHR argues that “[o]ver the last decades – thanks to the development of scientific knowledge on the subject – the States of the international community have reached consensus on existential risks and have identified specific anthropogenic behaviours that can irreversibly affect the interdependence and vital balance of the common ecosystem that make the life of species on the planet possible.” (para. 288). In other words, when existential risks are at stake, peremptory norms are necessary to prevent ultimate collapse. 

The IACtHR has rightly identified the magnitude and legal importance of the climate crisis. The IACtHR then proceeds to give examples of the most severe environmental harms, such as irreversible deforestation of primary forests essential for biodiversity and climate regulation, massive species loss and habitat destruction, persistent pollution of freshwater, oceans and the atmosphere with long-lasting toxic effects, and the irreversible disruption of natural biogeochemical cycles like carbon and nitrogen that sustain planetary life, particularly through extreme climate change impacts. These types of large-scale environmental destruction are also candidates for the emerging international crime of ecocide.

The IACtHR follows this with the conclusion that the fundamental rights to life, integrity, and health of all species create a binding obligation to halt human activities that threaten planetary ecosystem balance. Since preserving our common ecosystem is essential for enjoying other fundamental rights, the prohibitions against such destructive behaviours are so fundamental that they constitute jus cogens (para. 291).

No Derogation Permissible as an Argument for Jus Cogens

From a legal perspective, the prohibition of conduct that irreversibly threatens the vital balance of interdependent ecosystems necessary for present and future generations derives from general principles of law. Especially important is the principle of effectiveness, which ensures that recognised rights and obligations are applied to achieve their purpose. The IACtHR here argues from first principles because the obligation not to create irreversible damage to the climate and the global environment would be ineffective if it could be overridden by international treaties or mere State consent. The IACtHR’s emphasis on the principle of effectiveness is worth highlighting. As Crawford explains, “[i]n the literature, the principle of effectiveness (ex factis jus oritur) is often set against the principle of legality (ex injuria jus non oritur). A decentralized custom-based system in which sovereignty is a cardinal value must necessarily have regard to considerations of effectiveness.” (p. 580). In other words, the emphasis on effectiveness by the IACtHR underlines perhaps a certain unease about its lack of global recognition by the international community of States. Arguably, the IACtHR did not have to rely so heavily on effectiveness. According to the principle of legality, there are good arguments to recognise the jus cogens character of a norm in light of new scientific insights that can identify if an action or omission constitutes an irreversible existential threat. 

It should be highlighted that the IACtHR here does not follow the methodology recommended by the ILC on the identification of jus cogens. The ILC wrote that jus cogens must be “accepted and recognised by the international community of States as a whole” (2022 Draft ILC Conclusions), meaning a “very large and representative majority of States”. Some might question that this acceptance exists with respect to avoidance of climate harms, given that in the Advisory Proceedings before the ICJ, several States explicitly contested the jus cogens character of all or any climate norms. On the other hand, it is perhaps harder to identify customary norms when the UNFCCC and the Paris Agreement have near-universal membership, since this makes it difficult to identify State practice and opinio iuris as distinct from treaty compliance. 

It can be argued that, if human life on Earth faces an existential threat, the requirement for acceptance and recognition by the international community of States as a whole should be interpreted more dynamically. Indeed, even according to the ILC Draft Conclusions, it is not the mere mechanical number of States that counts for the acceptance but rather acceptance and recognition by the international community of States as a whole. This necessitates that such “acceptance and recognition transcend regional, legal systemic, and cultural boundaries, thereby ensuring broad representation across diverse juridical traditions and geographical constituencies”, which arguably exists in the case of irreversible damage to the climate and the global environment.

Four Key Reasons for the IACtHR’s Jus Cogens Recognition

The IACtHR establishes four key reasons for the jus cogens recognition. 

First, there is a clear dependency between protecting fundamental rights (life, integrity, health, non-discrimination) and prohibiting anthropogenic conduct with irreversible ecosystem impact, as ecosystem preservation is a sine qua non condition for all human rights validity. 

Second, legally recognising the obligation to preserve ecosystem balance against irreversible anthropogenic damage reflects humanity’s collective interest and is necessary—not merely convenient—for fulfilling existing international human rights obligations with no alternative guarantee. 

Third, this obligation has solid grounding in general legal principles, fundamental human rights, and growing international consensus, making its recognition legally sound rather than arbitrary. 

Fourth, recognising this obligation as a non-derogable norm does not contradict existing positive law but rather enhances comprehensive compliance with existing norms, reaching sufficient consolidation and universal recognition to justify its characterisation as jus cogens due to its indispensable connection to human life, dignity, and intergenerational justice. Further, State practice, multilateral environmental treaties, UN General Assembly resolutions, and regional court jurisprudence constitute progressive consolidation toward emerging legal recognition of the non-derogable prohibition of irreversible environmental damage. 

The principle of effectiveness, combined with considerations of dependence, necessity, universality of underlying values, and non-contradiction with existing law, provides the legal foundation for recognising the imperative prohibition of massive and irreversible environmental damage while contributing to compliance with already recognised international legal obligations. (paras. 292-294).

From La Oroya to AO-32/25

The IACtHR previously found in La Oroya v. Peru (2023) that obligations that “protect the environment against unlawful or arbitrary conduct that causes serious, extensive, lasting and irreversible damage to the environment in a scenario of climate crisis that threatens the survival of species” require “the progressive recognition of the prohibition of conducts of this type as a peremptory norm (jus cogens) accepted by the international community as a whole as a norm from which no derogation is permitted (para. 129, La Oroya)”.

In AO-32/25, the IACtHR followed its reasoning in La Oroya closely (see above ‘survival of species’), but with one important difference. Rather than reflecting on the “progressive recognition,” the IACtHR in the AO recognised the jus cogens character. No longer is there an argument about the progressive recognition of a future development, but rather, in AO-32/25, the IACtHR recognised the jus cogens character as lex lata. In other words, the IACtHR went one decisive step further than in La Oroya.

The IACtHR has long taken a more liberal view of imperative norms of international law. For example, it recognised “at the present stage of the development of international law, [that] the fundamental principle of equality and non-discrimination has entered into the domain of jus cogens. The legal framework of national and international public policy rests upon it and permeates the entire legal order.” (para 590 AO, citing Cfr. Opinión Consultiva OC-18/03, supra, para. 101, y Caso Dos Santos Nascimento y Ferreira Gomes Vs. Brasil, supra, para. 92).

Support in the Interventions before the ICJ

Several intervenors in the ICJ Advisory Opinion argued that climate norms may have jus cogens status, either through their connection to self-determination or as standalone obligations. Vanuatu and the Melanesian Spearhead Group suggested that the right to a healthy environment, essential to self-determination, may itself constitute a jus cogens norm, citing submissions by Samoa and El Salvador. El Salvador asked the Court whether this right is evolving into a peremptory norm. Panama and Ghana stressed the possible jus cogens character of large-scale atmospheric pollution and climate destruction. Burkina Faso argued that protecting the climate is an erga omnes and jus cogens obligation, triggering the legal consequences of international liability. Kiribati linked the recognition of the right to a healthy environment as a jus cogens norm to sovereign equality and intergenerational equity. In addition, the IACtHR’s own La Oroya judgement was approvingly cited before the ICJ by Barbados, St. Lucia and by the IUCN .

It should be noted that these interventions come from all parts of the world and thus transcend regional, legal systemic, and cultural boundaries, thereby ensuring an emerging broad representation across diverse juridical traditions and geographical constituencies, as required for jus cogens norms. 

Consequences of Recognising Irreversible Climate Harm as Jus Cogens

The legal consequences of the recognition as jus cogens of the obligation not to create irreversible damage to the climate and the global environment are profound. Treaties violating the norm are void, customary international law rules cannot exist, nor does the persistent objector rule apply. Unilateral acts are invalid, and acts of international organisations have no legal effect. In domestic law, any jus cogens prohibition should not just trigger domestic prohibitions for such actions but would normally incur criminal sanctions. If your State has a climate-denying Head of State or Government and their decisions violate the emerging jus cogens obligation not to create irreversible damage to the climate and the global environment, then international liability and action by the international community as a whole should follow. This somewhat surprising finding by the IACtHR might become one of its most consequential yet.