A Climate Dialogue Between International Courts: A Snapshot of the ICJ and I/A Court H.R. Advisory Opinions

For the first time, international courts are speaking with one voice: governments cannot ignore the climate emergency—and the fossil fuels driving it— without violating human rights. Two of the world’s most powerful courts have, within weeks of each other, delivered landmark rulings that cement climate change as a human rights issue under international law.

From scientific consensus to judicial consensus on climate

Together, the advisory opinions on climate change from the Inter-American Court of Human Rights (I/A Court H.R.) and the International Court of Justice (ICJ), both grounded in the undeniable science, joined the growing judicial consensus on the legal bases for climate action and climate justice. 

In July 2025, the I/A Court H.R. and ICJ issued back-to-back rulings affirming that climate change impairs the enjoyment of human rights (I/A Court H.R. 90, 118, 377, 393-457; ICJ 73, 376, 386, 403), implicating well-established obligations under international human rights law to prevent and remedy harm, and reasserting States’ legal duties in the face of the escalating climate emergency.

The ICJ’s attention to human rights – relatively rare (pp.130-31) in the jurisprudence of a Court focused primarily on inter-State relations – validates the centrality of human rights duties to climate action and accountability, elevating the I/A Court H.R.’s pronouncements and situating them solidly in the corpus of climate law. 

Even without any formal exchange between the judges, their climate advisory opinions constitute a judicial dialogue – a conversation not only across international institutions, but also with the myriad domestic tribunals called upon to apply the law to the inescapable facts of climate change, its known causes and its escalating consequences.      

Neither the I/A Court H.R.’s opinion nor that of the ICJ came in a judicial vacuum. They followed the first climate advisory opinion issued by the International Tribunal for the Law of the Sea (ITLOS) in May 2024, which concluded that States must prevent, reduce, and control anthropogenic greenhouse gas (GHG) emissions as a form of marine pollution. They also had the benefit of the European Court of Human Rights’ (ECHR’s) inaugural climate decision in 2024, KlimaSeniorinnen v. Switzerland, which held that insufficient climate action violates human rights. This triptych of advisory opinions, which provide authoritative international interpretations of binding climate duties, soon may be joined by a fourth, requested from the African Court on Human and Peoples’ Rights (ACHPR).

International opinions, global impacts

The climate advisory opinions have already been cited in pleadings in ongoing cases and will continue to guide the rising tide of climate litigation around the world. But their influence does not stop there; they also have the power to shift policymaking at the domestic and international levels.

 Past advisory opinions have had significant political and legal impacts. For example, the ICJ’s nuclear weapons advisory opinion shaped the subsequent negotiations of the Treaty on the Prohibition of Nuclear Weapons, while its Chagos advisory opinion set out the legal imperative for the United Kingdom to return the Chagos Islands to Mauritius after years of colonial rule, which the UK subsequently did. The I/A Court H.R.’s advisory opinions likewise have influenced domestic policy-making and litigation, as well as contentious cases before other human rights bodies. In Sacchi et al. v Argentina et al. (10.5), for example, the UN Committee on the Rights of the Child took note of the I/A Court H.R.’s Advisory Opinion OC-23/17 on the environment and human rights in considering claims that the inadequacy of States’ climate action violated the rights of youth.

Distinct advisory authorities, complementary conclusions

With distinct jurisdictions, each international court enriches the understanding of the legal obligations implicated by the climate crisis. Among the five international courts with advisory jurisdiction — ITLOS, ICJ, I/A Court H.R., ACHPR, and ECHR — the ICJ has the broadest authority, derived from the Charter of the United Nations, to address any legal question and to draw on all relevant sources of international law, both customary and treaty-based. That mandate endows the ICJ’s opinions with uniquely wide-ranging application.

In contrast, the principal competence of the I/A Court H.R is the interpretation of the American Convention on Human Rights (ACHR). However, the I/A Court H.R. is also authorized to interpret “other treaties concerning the protection of human rights in the American states,” which can include (i) human rights treaties adopted by the Organization of American States (OAS), (ii) non-regional human rights treaties ratified by the American States, and (iii) any provisions dealing with the protection of human rights included in any international treaty applicable in the American States. That means the legal guidelines articulated by the I/A Court H.R in its recent climate opinion set out the obligations not only of States Parties to the ACHR but all OAS member states (41). The opinions also carry persuasive weight before other regional bodies, such as those of the African human rights system, which have drawn on Inter-American jurisprudence in their own deliberations.

These differences between the courts make the consistencies across their advisory opinions all the more striking. Far from the fragmentation or conflicting interpretations some feared when the parallel advisory proceedings were announced, the rulings reinforce the value of institutional diversity and complementarity.      

Historic participation leads to legal transformation
The opinions’ transformative outcomes can be directly tied to the peoples’ movements behind them and the unprecedented levels and quality of participation they saw. The I/A Court H.R was remarkably open, inviting not only States and international organizations, but local communities, Indigenous Peoples and Afro-descendant groups, civil society organizations, academic institutions, and youth activists to join the written and oral proceedings. The Court received a record 263 submissions from 613 different actors – as well as the Manaus Declaration on Human Rights in the Climate Emergency, signed by over 400 groups – and the historic hearings held in Barbados and Brazil benefited from the arguments and testimonies of some 185 delegations.

While the ICJ’s procedure is far more restrictive, the youth movement and transnational alliances for climate justice that propelled the issue of climate change to the world’s highest court influenced the formal proceedings in numerous ways. They shaped the content of arguments presented and the composition of delegations, convincing some States to convey witness testimony and include youth representatives. The nature of the participation transformed the tenor of the oral hearings, which saw interventions by over 100 States and international organizations throughout ten days, including many appearing before the Court for the first time. More profoundly, it marked a shift in perspectives on, and the practice of, international law at the Court and beyond.

This robust engagement not only enhanced the legitimacy and authority of the climate advisory proceedings in both courts; it also enriched their analyses and fundamentally strengthened their conclusions.

Points of convergence and complementarity

The advisory opinions put to rest the notion that the UN Framework Convention on Climate Change (UNFCCC), Kyoto Protocol, and Paris Agreement are merely voluntary commitments with no teeth. These climate agreements impose binding and enforceable obligations that require countries to reduce GHG emissions rapidly and with progressively more ambition. Far from entirely discretionary undertakings, mitigation measures must be: capable of limiting temperature rise to 1.5°C (which the ICJ affirms as the scientifically based legally binding global temperature goal); in line with science; according to States’ historical responsibilities and current capabilities; and consistent with their other international duties (I/A Court H.R.128, 323-37; ICJ 213, 236, 241-49, 268-70).  Reading the climate treaties in light of concurrent human rights obligations, both courts affirm that the required climate action must meet substantive standards sufficient to protect human rights from climate harm.

 While the climate treaties require far more than polluting countries contend, they are far from the only source of climate obligations. The ICJ squarely dismisses the notion that climate treaties are “lex spexialis” with respect to either States’ primary duties or the rules governing their responsibility for breaches (164-71, 418-20). Climate duties neither start nor end with the UNFCCC and Paris Agreement, and, as ITLOS said, complying with Paris does not discharge all of a State’s climate obligations (ITLOS 223-24; ICJ 314-315). Both the I/A Court H.R. and ICJ root the legal duties to prevent and remedy climate harm in multiple sources of law, including longstanding treaty-based and customary human rights and environmental law, which the ICJ made clear were not displaced by the climate treaties. Instead, they inform how those agreements must be interpreted and implemented (I/A Court H.R. 324-335; ICJ 404 ).

The courts’ reliance on customary international law, which binds all States, broadens the applicability of their conclusions beyond the parties to any particular convention or treaty. The longstanding duty to prevent significant transboundary environmental harm —which the I/A Court H.R. likens to the duty to prevent human rights violations— (I/A Court H.R. 275-78; ICJ 132-39; 440) and the duty to cooperate (I/A Court H.R., 149, 247-65; ICJ 140-42) are among the most important customary rules invoked by both courts. The I/A Court H.R. goes so far as to declare the prohibition on generating irreversible damage to the environment “jus cogens,” a peremptory norm that cannot be set aside and that all States must follow (287-294), suggesting that conduct known to cause such damage, like fossil fuel expansion, must cease. The ICJ, in turn, emphasizes the erga omnes nature of climate obligations, meaning that they are owed to the international community as a whole, and are enforceable by all States (439- 440). 

Grounding climate obligations in different bodies of law, from environmental and human rights treaties to customary principles, opens the door to both inter-state cases and claims by individuals and communities on human rights grounds.

Such claims are likely to increase, because, as both courts recognize, climate change puts all human rights at risk (I/A Court H.R.90, 118; ICJ 73, 376, 386, 403). Whereas the ICJ’s analysis remains general, the I/A Court H.R. paints a picture of climate harm in the region, highlighting its disproportionate impacts on those in vulnerable situations (104-119) and identifying corresponding protections owed to them. Crucially, both courts affirm the right to a healthy environment as fundamental to the enjoyment of other rights (I/A Court H.R. 377; ICJ 393) and threatened by climate change. Although the ICJ stops short of opining on the customary status of that right (as Judges Aurescu and Tladi lament in separate opinions), the I/A Court H.R.  expounds its content and derives from it the right to a healthy climate (298-304). Unpacking what the different rights at stake require, including economic, social, and cultural rights, the I/A Court H.R. consolidates a robust framework for access rights (488-560), and articulates a special duty of protection owed to environmental defenders (566-67). For the first time at the international level, the I/A Court H.R.  also identifies Nature as a subject of rights (279-286).

States must use all means at their disposal to protect human rights from climate harm. Both courts emphasize that the due diligence necessary to satisfy preventive obligations requires regulation of business conduct (I/A Court H.R. 321-22; ICJ 428) – including emitting activities and disinformation (I/A Court H.R 524-29) or other obstruction of climate action (I/A Court H.R. 347). But the I/A Court H.R. goes further, recognizing disinformation as a key social driver of climate change and outlining State obligations to combat it (488-529). Significantly, the I/A Court H.R. adds that businesses also have independent obligations under human rights law to ensure their activities do not contribute to climate-related human rights violations and when they do, must take steps to remedy resulting harm (345-46).

Fulfilling climate obligations means phasing out fossil fuels. Although both courts recognized the scientific reality that fossil fuels are the primary driver of the anthropogenic GHG emissions causing climate change (I/A Court H.R. 47; ICJ 72, 81, 85), and the need to regulate their activities (I/A Court H.R. 350-53), the ICJ further put fossil fuel producers on notice, by naming that the failure to protect the climate system from “fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licenses or the provision of fossil fuel subsidies,” may “constitute an internationally wrongful act which is attributable to that State” (427). Such wrongful acts carry legal consequences, including the duties to cease the breaching conduct, provide guarantees of non-repetition, and provide full reparations for resulting injuries. As the ICJ said, cessation of a wrongful act may require the revocation of administrative, legislative, and other measures (447), which in the case of fossil fuels may mean revoking licenses, subsidies, or other permissions that support fossil fuel production and use.

Read together, the opinions solidify the bases for remedy and reparation of climate harm under both the law of State responsibility (ICJ 420) and human rights law (I/A Court H.R. 556-59). On the substantive scope of climate justice, the ICJ invokes “the entire panoply of legal consequences provided for under the law of State responsibility” (445), which largely parallels the range of redress measures the I/A Court H.R. lists, citing its reparations jurisprudence (556-559). The I/A Court H.R also addresses procedural dimensions, including access to justice, and the ICJ opines that States may be required to reduce their GHG emissions as a duty of cessation and guarantees of non-recurrence (447-56). But neither court addresses climate reparations in concreto, leaving the promise of their conclusions to be tested another day.

What comes next?

The climate advisory opinions are poised to jumpstart stalled international climate negotiations and resuscitate listless national climate policies that continually fail to meet the urgency of the moment, in line with what the science requires and justice demands. The courts’ pronouncements provide negotiators with tools to ground diplomatic discussions not in political opinion but in legal obligation, and equip litigators and frontline community members with arguments to hold States and businesses accountable under both international and domestic law. Crucially, the ICJ’s reinforcement of the human rights duties to prevent, mitigate, and remedy climate harm, duties elaborated by the I/A Court H.R., opens avenues for individuals and communities to pursue climate justice and invites other human rights institutions to engage. It also makes clear that climate change is not the exclusive domain of technical experts, but the lived reality of individuals and communities around the world who are not only authorities on its impacts, but authors of its solutions.