Building a Corpus Iuris Climatis : Making Sense of the ICJ and the IACtHR Advisory Opinions on Climate Emergency

Abstract

In 2025, the International Court of Justice (ICJ) and the Inter-American Court of Human Rights (IACtHR) delivered landmark advisory opinions that redefined the intersection between environmental protection, human rights, and climate governance. Although grounded in distinct mandates and legal traditions, both opinions engage with the same foundational principles of due diligence, prevention, cooperation, and intergenerational equity. Their reasoning also exposes deeper questions about the interaction between universal and regional jurisdictions, the role of scientific expertise in judicial interpretation, and the limits of legal imagination in confronting the global climate crisis. By tracing the convergences and tensions between these two judicial voices, the article explores whether international law is entering a new phase in its response to the juridification of the climate emergency.

Introduction

The year 2025 marks a watershed in the legal articulation of the relationship between human rights, environmental integrity, and climate governance. In parallel advisory opinions, the International Court of Justice (ICJ) and the Inter-American Court of Human Rights (IACtHR) directly addressed the normative status of the right to a clean, healthy, and sustainable environment (R2CHE) and clarified the scope of States’ obligations in confronting the climate emergency. Although distinct in mandate and jurisprudential technique, both courts converge in affirming that the enjoyment of fundamental rights—including life, health, food, water, housing, and cultural integrity—cannot be ensured without the protection of the environment and the stability of the climate system. ¹

The ICJ, acting upon a request from the United Nations General Assembly (UNGA) ² that “recognized the legal dynamics of this crisis” ³ was tasked with “general framework for mapping” ⁴ obligations of States under international law to protect the climate system and other parts of the environment from anthropogenic greenhouse gas emissions, both in their relations with other States and for the benefit of present and future generations. It also asked the Court to clarify the legal consequences that arise from those obligations when States, through their acts or omissions, cause significant harm to the climate system or other parts of the environment—particularly in relation to: (i) other States, especially small island developing States that, due to their geographic circumstances and level of development, are particularly vulnerable to the adverse effects of climate change; and (ii) peoples and individuals, both of the present and future generations, who suffer those same harmful effects. ⁵

The IACtHR, by contrast, at the request of Colombia and Chile, exercised its advisory competence to clarify the scope of States’ obligations to respect, ensure, and adopt necessary measures in response to the climate emergency across three dimensions: (1) the protection of substantive rights—such as the rights to life, health, personal integrity, housing, water, food, work, culture, and a healthy environment—against the impacts of climate change; (2) the fulfilment of procedural rights, including access to information, public participation, and access to justice in environmental matters; and (3) the enhanced and non-discriminatory protection of vulnerable groups—such as children, women, Indigenous peoples, Afro-descendant and rural communities, and environmental human rights defenders—facing the threats and effects of the climate crisis. ⁶ The Court thus situated the climate emergency within the framework of the American Convention on Human Rights ⁷ and the San Salvador Protocol. ⁸

This article examines the two advisory opinions through three interrelated levels of analysis. The first concerns a transversal political dimension: both courts grounded their legal reasoning in the scientific assessments of the Intergovernmental Panel on Climate Change (IPCC). While the IPCC represents the most authoritative synthesis of global scientific consensus, its reports are also the product of intergovernmental negotiation and thus reflect political compromise as well as scientific evidence. By embedding IPCC findings within their reasoning, both the ICJ and the IACtHR effectively juridified science that is itself partially politicized, integrating it into the normative framework of international law. ⁹

A second level of analysis focuses on the normative dimensions of the two advisory opinions, analysing how each contributes—through different interpretive approaches—to the development of the legal framework on climate emergency and environmental protection. Their influence unfolds on three planes: first, the clarification and consolidation of existing principles such as due diligence, prevention, and international cooperation; second, the articulation of distinct judicial perspectives on interpretive principles like precaution, equity, sustainable development, and common but differentiated responsibilities; and third, the introduction of normative innovations that extend the frontiers of international law. In this last regard, the IACtHR's recognition of an autonomous right to a healthy climate, its incorporation of procedural guarantees, and its elevation of the prohibition of irreversible environmental harm to the status of jus cogens contrast with the ICJ's more cautious reaffirmation of erga omnes environmental obligations.

The third level of analysis addresses the potential for fragmentation in international environmental/climate law resulting from the courts’ divergent interpretative methodologies. Although both opinions seek to strengthen accountability, their differing orientations—one grounded in the logic of general international law, the other in a rights-centred hermeneutic—pose challenges for coherence and uniformity. This divergence prompts a central question: does such plurality of reasoning enrich the adaptability and resilience of international law, or does it risk undermining the consistency and effectiveness of the collective legal response to the climate crisis?

Finally, the article concludes with some reflections on the broader implications of this judicial interaction for the evolution of international law. It considers whether the dynamic relationship between universal and regional jurisdictions signals a new phase of cooperative pluralism—one that balances systemic coherence with normative innovation in addressing the most pressing challenge of our time: the juridification of the global climate emergency.

Recognition of Climate Change as a Threat to the International Legal Order

In their 2025 advisory opinions, both the ICJ and the IACtHR move beyond framing climate change as a discrete environmental challenge and instead characterize it as a systemic threat to the stability of the international legal order and the effective enjoyment of human rights. This systemic framing elevates climate change from a technical or sectoral concern to a foundational test of law, justice, and institutional legitimacy.

The ICJ describes the climate crisis, defined by the UN General Assembly as a “common concern of mankind” ¹⁰ , an “urgent and existential” challenge that directly implicates the baseline of inter-State obligations and the protection of common interests of the international community. It emphasizes that States are bound by the duty to prevent “significant harm” to the climate system through due diligence, situating this obligation firmly within customary international law. Crucially, the Court makes clear that this duty is not confined to direct transboundary contexts but also extends to activities with direct or cumulative global impacts, such as greenhouse gas emissions. In so doing, the ICJ recognizes the climate system and other parts of the environment as legal interests protected under international law, thereby signalling a shift in emphasis: the environment is no longer conceived merely as a backdrop for human activity but as a shared interest whose integrity is indispensable to the international community as a whole. ¹¹ In this framing, traditional legal concepts—territorial sovereignty ¹² , transboundary harm, and State responsibility—must be reinterpreted to address the planetary interconnectedness of climate processes.

The IACtHR affirms that climate change is not merely an environmental risk but a crisis that creates “extraordinary and increasingly serious risks” that threaten not only individual rights such as life, health, food, water, and housing but also the coherence of the Inter-American system itself. ¹³ Unlike the ICJ's focus on inter-State obligations, the IACtHR emphasizes intragenerational and intergenerational equity, highlighting the disproportionate burdens borne by Indigenous peoples, children, and those living in poverty. ¹⁴ The Court further links climate harms to systemic consequences, including forced migration, loss of livelihoods, and ecosystem collapse. ¹⁵ To address these challenges, it calls for recognition of a right to a healthy climate as an autonomous dimension of the right to a healthy environment, thereby advancing a rights-centred normative innovation that integrates environmental protection, sustainable development, and resilience. ¹⁶

Analytically, the systemic threat framing adopted by both courts performs three critical functions. First, it elevates normative ambition by positioning climate emergency as a central test of the capacity of international law to govern global collective challenges. Second, it legitimizes cross-cutting remedies, requiring institutional responses that transcend the traditional silos of environmental protection and human rights. ¹⁷ Third, by framing climate change as a threat to the coherence of law itself, the ICJ and the IACtHR reinforce the view that obligations of prevention, cooperation, and rights protection occupy a central place in the contemporary legal order, resistant to claims of exceptionalism or non-justiciability. ¹⁸

The Role of Science and the Authority of the IPCC

Before turning to the legal analysis of the advisory opinions, it is important to examine the role of science—and, more specifically, the authority accorded to the Intergovernmental Panel on Climate Change (IPCC)—in their reasoning. Since its creation in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), the IPCC has functioned as the primary epistemic source on climate change, synthesizing thousands of peer-reviewed studies into assessment reports. ¹⁹ Both the ICJ and the IACtHR explicitly grounded their reasoning in IPCC findings, treating them as the scientific baseline for assessing the scale, causes, and foreseeable impacts of climate disruption. ²⁰

Yet it would be misleading to portray the IPCC as a purely scientific body detached from politics. Its reports are the product of a hybrid process: while the scientific chapters are authored by independent experts, the “Summary for Policymakers”—the section most often cited by courts and international organizations—is negotiated and approved line by line by the representatives of 195 States. ²¹ As scholarship has shown, this negotiation process often reflects geopolitical interests. ²² It also worth mentioning that developing countries face additional challenges in multilateral negotiations: underdevelopment constrains their ability to train experts, participate in negotiations, and influence drafting processes. Even within democratic institutions such as the IPCC, where formal voting rights are equal, effective influence is mediated by resources, expertise, and negotiating capacity.

The IPCC is thus best understood as a boundary institution operating at the science–policy interface, where epistemic authority and political compromise coexist in constant tension. This dual character has direct implications for international adjudication. By grounding their legal analysis in IPCC assessments, the ICJ and IACtHR have juridified a body of knowledge that is at once scientific and political. The consequence is twofold. On the one hand, reliance on IPCC findings anchors judicial reasoning in the most authoritative global consensus available, insulating courts from accusations of arbitrariness. On the other, it means that politically mediated science acquires the force of law, importing into adjudication the compromises and ambiguities inherent in intergovernmental negotiations. Contested issues such as carbon budgets, tipping points, or the allocation of responsibility among high-emitting States are therefore not only scientific but also political questions—ones that international courts reinterpret as legal standards through their reliance on IPCC reports.

The ICJ and IACtHR adopt distinct strategies in managing this entanglement. The ICJ primarily uses IPCC evidence to substantiate the scope of the customary obligation of prevention and due diligence in light of contemporary scientific knowledge, without delving into contested distributional debates. ²³ The IACtHR, by contrast, engages with IPCC findings more expansively, using them to broaden the normative horizons of human rights law—for example, in affirming the recognition of an autonomous right to a healthy climate and in linking scientific evidence to the peremptory character of obligations to prevent irreversible harm. ²⁴

Geopolitically, this reliance underscores a deeper reality: the architecture of climate law is shaped not only by States and treaties but also by knowledge-producing institutions that mediate power relations. That both the ICJ and the IACtHR relied so heavily on IPCC assessments signals that, in the climate field, science has become the evidentiary backbone of law. Yet because IPCC science is itself partly the outcome of negotiated processes, judicial reliance on it may inadvertently reflect and reinforce the underlying political compromises embedded in its production. For international law, the central question is whether such reliance enhances legal certainty by grounding obligations in an authoritative scientific consensus, or whether it risks constraining normative development by situating adjudication within the limits of politically mediated knowledge.

Sources of International Law and Methods of Interpretation

As is often the case in international adjudication, the competences of tribunals, the interpretive methods they privilege, and the sources they rely on shape the outcomes they reach. The 2025 advisory opinions of the ICJ and the IACtHR illustrate this dynamic vividly. Indeed, the starting point of each Court was different: International Human Rights Law was analysed by the ICJ along with other sources of international law, particularly regarding climate change and other parts of the environment, while for the IACtHR, as expected, International Human Rights Law was the main lens through which it assessed the sources that the ICJ had used to reach its conclusions. This essential difference illustrates the hermeneutical approach employed by the two Courts. The ICJ adopted a state-centred, positivist method to answer the request of the United Nations General Assembly (UNGA), while the IACtHR used a rights-centred, justice-driven approach to address the opinions requested by Chile and Colombia. Undoubtedly, this led to completely distinct results and shaped all the elements that compose the two advisory opinions now under examination.

Despite the different methodologies employed by the courts, a central point of convergence between the two advisory opinions lies in their reliance on a broad spectrum of international law sources. Both tribunals frame climate obligations through the categories identified in Article 38 of the ICJ Statute—treaties, customary international law, and general principles of law—while also relying on interpretive principles and drawing support from institutional practice and soft law.

In this respect, the ICJ grounded its opinion only in sources it deemed directly relevant to the questions posed. Yet it did not entirely confine itself to this framework, expressly acknowledging the potential relevance of other regimes of international law—such as international trade and investment law, and even international humanitarian law where armed conflict intersects with climate-related harm. ²⁵ The IACtHR, by contrast, engaged with many of the same international treaties, customary norms, and principles referenced by the ICJ, but treated them primarily as interpretive tools, subordinated to the core sources of its regional human rights framework. ²⁶

At the core of their reasoning, both courts treat multilateral environmental agreements as the backbone of the applicable legal framework, seeing them as interconnected instruments that collectively define States’ obligations in addressing climate change. It worth mentioning that the ICJ held that climate change treaties are not the sole applicable law and do not exclude other rules of international law under lex specialis. ²⁷ Beyond treaties, both courts reaffirm customary obligations—particularly the duties to prevent significant transboundary harm, due diligence and to cooperate—underscoring that climate obligations are not confined to individual instruments but are embedded within a systemic and coherent body of international law. ²⁸

Human rights law constitutes an additional pillar of convergence between the two courts, yet each emphasizes different dimensions. Since the ICJ situates climate obligations within the broader corpus of international law, it referenced universal human rights instruments ²⁹ alongside customary human rights norms. For its part, the IACtHR interprets climate obligations embedding them directly within the Inter-American human rights system, particularly the American Convention on Human Rights (1969) and the Protocol of San Salvador (1988) ³⁰ , and draws extensively on regional and subregional environmental instruments. ³¹

Both tribunals also rely on principles to clarify the scope and content of States’ obligations. The ICJ identifies sustainable development, common but differentiated responsibilities and respective capabilities, equity, intergenerational equity, and the precautionary approach ³² as interpretive tools embedded in treaties and customary law. ³³ The IACtHR incorporates all those principles, embedding them within a broader human rights framework and linking them to traditional rights principles—pro persona, best interests of the child, progressivity, and non-discrimination—while also emphasizing climate-specific principles such as pro natura, precaution, prevention, polluter pays, and intra- and intergenerational equity. ³⁴ Both tribunals thus confirm that principles function not as optional guidance but as normative tools essential for interpreting and operationalizing binding obligations.

Jurisprudence further reinforces the interpretive frameworks of both courts. The ICJ, for instance, employed this auxiliar law source to clarify obligations of prevention, due diligence, and environmental impact assessment. ³⁵ Similarly, the IACtHR, for instance, draws on its advisory opinions ³⁶ and contentious jurisprudence, ³⁷ to affirm the interdependence of human rights and environmental protection. In both instances, prior jurisprudence is used persuasively to expand the normative content of climate-related obligations.

Finally, both the ICJ and the IACtHR drew on soft law and institutional practice to contextualize and reinforce States’ climate obligations. The ICJ referred to instruments such as the WHO's Report on Health, Environment and Climate Change, Human Rights Council Resolution 53/6, and UNGA Resolution 76/300, which recognizes the right to a clean, healthy, and sustainable environment. ³⁸ The IACtHR, meanwhile, invoked, for example, the Rio Declaration, the UN Guiding Principles on Business and Human Rights, and the same UNGA resolution, emphasizing the human rights dimension of environmental protection. ³⁹ It also highlighted the role of economic and trade institutions, including the World Bank and International Monetary Fund, in shaping the operationalization of climate finance and policy. ⁴⁰ While neither court treats these instruments as binding, both use them as persuasive authority to reinforce systemic integration between climate and human rights norms. ⁴¹

Convergences, Perspectives and Innovations

Because of the convergences in their sources, the advisory opinions of the ICJ and the IACtHR have jointly shaped a set of normative concepts in international law, advancing both the scope of State obligations and the recognition of rights in the context of climate change and environmental degradation. The normative contribution of these advisory opinions may be understood on three levels: first, in the clarification and consolidation of pre-existing principles; second, in the articulation of distinct judicial perspectives on certain of those principles; and third, in the formulation of genuine innovations that broaden the normative framework—albeit at times giving rise to doctrinal tensions or potential fragmentation.

These three dimensions of contribution are sometimes aligned but also reveal important differences in the approaches of the two Courts. Convergence is most evident in the recognition of customary obligations such as prevention of transboundary harm, due diligence, and international cooperation, where the ICJ and the IACtHR progressively clarify their scope and adapt them to the specific challenges of climate change. Alongside these obligations, and as it was above-mentioned, both Courts also rely on interpretative and integrative principles such as precaution, sustainable development, equity, the polluter pays principle, common but differentiated responsibilities and respective capabilities (CBDR-RC), restoration, and intergenerational equity. Yet the weight assigned to these principles differs markedly: The ICJ has generally approached such principles with caution, employing them primarily as tools of systemic integration or as balancing mechanisms within general international law. By contrast, the IACtHR has adopted a more robust stance, treating them as normative standards by directly linking precaution, equity, the polluter-pays principle, and non-discrimination to the protection of human rights, while reframing sustainable development and CBDR-RC in terms of distributive justice and the realization of rights for both present and future generations. This divergence of emphasis reflects not only methodological differences but also distinct normative ambitions: the ICJ situates environmental protection within the framework of general international law, whereas the IACtHR interprets it through a rights-centred lens that integrates both substantive and procedural dimensions of climate justice.

Innovation emerges in more groundbreaking developments, where the two Courts diverge in both emphasis and normative ambition. The IACtHR has been at the forefront of conceptual expansion by recognizing an autonomous human right to a healthy climate and by integrating procedural guarantees—such as access to information, participation, justice, and the protection of environmental defenders—into the core architecture of climate governance. It further advanced the normative hierarchy by identifying that certain environmental obligations, including the prohibition of irreversible climate damage, acquire the status of jus cogens, thereby affirming their peremptory and non-derogable nature. The ICJ, while not reaching this level of normative elevation, contributed by emphasizing the erga omnes character of environmental obligations, reinforcing their universal applicability and systemic role within general international law. Taken together, these developments illustrate how both Courts are progressively stretching the contours of international law to accommodate the singular challenges posed by climate emergency and environmental degradation. Significantly, the IACtHR also broadened the circle of beneficiaries: in addition to individuals and communities, it explicitly recognized future generations and nature itself as holders of legal interests, thereby consolidating an eco-centric and intergenerational orientation within the Inter-American human rights system

Against this backdrop, the following sections examine these three dimensions in detail, beginning with the clarification and consolidation of customary principles such as the duty to prevent transboundary harm.

Customary Obligations

The Principle of Prevention of Transboundary Harm

The principle of prevention of transboundary harm has long been a cornerstone of international environmental law, requiring States to ensure that activities within their jurisdiction or control do not cause significant damage to the environment of other States or areas beyond national jurisdiction. ⁴² In their climate emergency advisory opinions, both the ICJ and the IACtHR reaffirmed that this principle constitutes a binding rule of customary international law applicable in the climate context.

Their approaches, however, diverge. The ICJ conceives prevention as an obligation of conduct directed to inter-State relations and articulated through due diligence, stressing that it applies not only to direct transboundary harm but also to activities with global consequences such as greenhouse gas emissions. The Court clarified that the duty arises both when harm has not yet occurred, but a risk exists, and when harm has already been caused with the risk of further damage, with the assessment depending on foreseeability and severity. It further highlighted that significant harm may result from cumulative effects of multiple activities, even if individually minor, and therefore States must assess aggregate impacts. The determination of significant harm, it added, must rely on the best available science—particularly IPCC reports – and States are required to adopt proportionate measures consistent with their capabilities. ⁴³

By contrast, the IACtHR situates prevention within the framework of the American Convention on Human Rights, treating it as a reinforced obligation owed to individuals and communities as well as to States. It emphasized that climate-related harm directly threatens the enjoyment of human rights and therefore requires anticipatory and precautionary measures, especially where risks are irreversible. ⁴⁴ The Court tied prevention to the standard of enhanced due diligence, which in the context of the climate emergency demands not only regulation and monitoring but also adaptation measures, access to information, and special protection for vulnerable populations as will be discussed below. ⁴⁵ In this way, the Court broadens both the circle of duty-bearers and the beneficiaries, marking a significant departure from the ICJ's inter-State framing.

The Duty of Due Diligence

Both the ICJ and IACtHR have consolidated due diligence as the governing standard of conduct in the climate change context. The ICJ has reaffirmed it as a rule of customary international law under the principle of prevention of transboundary harm, while the IACtHR has oscillated between recognizing its customary status and grounding it in the obligation to guarantee human rights under the American Convention. Together, their opinions elevate due diligence from a general principle into a multidimensional standard of binding international law. ⁴⁶

At the core, both courts reject the notion that due diligence is merely aspirational; they characterize it as a binding legal duty of conduct. They also agree that the standard is evolutive, adapting to advances in science, technology, and international norms. For the ICJ, the threshold of care intensifies where scientific knowledge indicates a high probability of significant harm, requiring States to update scientific data, cooperate technically, and prudently apply available technologies, calibrated by capabilities under the principle of common but differentiated responsibilities (CBDR-RC) ⁴⁷ Similarly, the IACtHR held that, given the foreseeability and severity of climate harms, States must comply with reinforced due diligence, requiring ambitious and proactive measures consistent with the best available science. ⁴⁸

This convergence is normatively significant: both courts reject any attempt to invoke scientific uncertainty as a justification for inaction. Instead, they integrate precaution and science into the legal content of due diligence, signalling that inaction in the face of foreseeable climate risks is incompatible with international law. ⁴⁹

The ICJ situates due diligence as the “primary standard of conduct” under the law of prevention. It requires States to adopt “all appropriate measures” within their power—legislation, administrative procedures, enforcement mechanisms, and monitoring systems—and confirms that the duty extends to both public and private operators. ⁵⁰ While private emissions are not directly attributable to States, a failure to exercise effective regulatory oversight amounts to a breach of due diligence. ⁵¹ Substantively, States must adopt preventive and precautionary measures; procedurally, they must conduct environmental impact assessments (EIAs) for activities posing significant risks, including greenhouse gas–emitting projects, and notify and consult with affected States. ⁵² The ICJ's strength lies in trying to consolidate a clear and objective universal baseline, but its reluctance to set concrete thresholds for emission reductions or adaptation risks entrenching a minimalist standard insufficient for the climate crisis.

The IACtHR has pursued a more dynamic trajectory. In its Advisory Opinion OC-23/17 (Environment and Human Rights), the Court recognized the duty to prevent significant environmental harm as part of customary international law, citing international precedents such as Trail Smelter, Corfu Channel, and Pulp Mills. ⁵³ In that opinion, the Court affirmed that the obligation extended even extraterritorially where a causal link could be established.

In the Advisory Opinion now under analysis, however, the Court reframed the source and content of due diligence. Rather than emphasizing its customary character, it rooted the obligation in Article 1(1) ⁵⁴ of the American Convention as part of the duty to guarantee human rights, developing it into a reinforced standard of due diligence considering the climate emergency. ⁵⁵ This reinforced standard includes a comprehensive set of measures: the thorough identification and assessment of climate risks; the adoption of ambitious and proactive preventive actions to avert worst-case scenarios; reliance on the best available science in the design and implementation of climate policies; the integration of a human rights perspective to ensure that measures do not generate or aggravate vulnerabilities; and the continuous monitoring of their impacts. It further entails strict compliance with procedural rights—access to information, participation, and justice—together with transparency and accountability in State action. Finally, reinforced due diligence also encompasses effective regulation of corporate climate responsibilities and strengthened international cooperation, particularly through technology transfer, financing, and capacity-building. ⁵⁶

The contrast seems clear. The ICJ consolidates due diligence as a customary, inter-State obligation under the principle of prevention, providing universality and legal certainty. The IACtHR, for its part, has moved from recognizing due diligence as customary (IACtHR OC-23/17) to developing it as a reinforced, rights-based obligation grounded in the American Convention (IACtHR 2025). While the ICJ offers a universal baseline, the IACtHR deepens its normative content, explicitly linking due diligence to human dignity, equality, and justice.

The Duty to Cooperate

The duty to cooperate occupies a central place in both advisory opinions, yet its treatment reveals not only convergence but also distinct normative emphases that underscore both the strengths and the limitations of international law in addressing climate change. Both the ICJ and the IACtHR affirm its binding character under customary and treaty law, framing cooperation as indispensable for confronting a global challenge that no State can resolve in isolation. Both also link cooperation to the principle of good faith, but while the ICJ conceives it as a requirement of legal certainty and compliance with treaty-based obligations, ⁵⁷ the IACtHR deploys it as a vehicle for equity and social justice within the human rights framework. ⁵⁸

For the ICJ, cooperation is primarily functional: it enables the operation of instruments such as the UNFCCC and the Paris Agreement, ⁵⁹ ensuring coordinated efforts particularly regarding financial assistance, technology transfer. It is particularly crucial to the achievement of collective objectives such as the stabilization of global temperature. ⁶⁰ By tying cooperation to due diligence and the prevention of transboundary harm, the Court not only consolidates it as customary law but also clarifies its role as an operative principle of climate governance.

The IACtHR, in turn, embeds cooperation directly within the obligation to guarantee human rights. It portrays cooperation as indispensable to protect the rights to life, integrity, housing, and property from climate impacts. ⁶¹ Its scope, however, is broader than that envisaged by the ICJ: it extends to financial and economic assistance for less developed countries, technical and scientific cooperation, technology transfers, and the joint implementation of mitigation, adaptation, reparative measures and the establishment of international forums and the elaboration of joint policies. ⁶² A distinctive feature of the IACtHR's reasoning is the linkage between cooperation and the principles of equity, social justice, and solidarity, stressing that States with greater capacities bear heightened duties of assistance. ⁶³ In this way, the Court reframes cooperation not merely as an operational tool but as a principle of climate justice, extending its reach beyond the environmental sphere to poverty eradication, the reduction of inequalities, and the protection of vulnerable groups in the climate emergency. This expansive interpretation illustrates the transformative potential of international law when approached through an evolutionary and integrative method of interpretation.

Interpretative and Integrative Principles

Interpretative principles have long served as mediating tools in international environmental law, enabling courts to adapt general norms to complex and evolving challenges. In their climate change advisory opinions, the ICJ and the IACtHR mobilized a range of such principles—including precaution, restoration, equity, common but differentiated responsibilities and respective capabilities (CBDR-RC), non-discrimination, sustainable development, and the polluter pays principle—not only as hermeneutical devices but also as instruments to broaden the normative scope of States’ obligations. Convergence emerges in their reliance on these shared principles, yet their interpretative strategies diverge significantly: the ICJ situates them within the framework of general international law, while the IACtHR reconceptualizes them as binding obligations embedded in the protection of human rights.

Risk, Prevention, and Restoration

The precautionary principle holds a central position in both advisory opinions. The ICJ linked precaution to the customary obligation of prevention, affirming that a State “would not meet its obligation of due diligence if it disregarded plausible indications of potential risks.” As it was above-mentioned, the Court clarified that precaution requires preventive measures even under conditions of scientific uncertainty. ⁶⁴ Judge Charlesworth further elucidates this distinction, observing that prevention addresses known risks, whereas precaution responds to scientific uncertainty. In the climate change context—where scientific consensus is comparatively robust—most conduct falls under the duty of prevention, though the precautionary principle retains relevance in situations characterized by residual or emerging uncertainty. ⁶⁵

The IACtHR echoed this view. Yet it endowed precaution with greater normative density. The Court required anticipatory measures in light of the irreversibility of climate harms, tied precaution to intergenerational equity—demanding that present generations adopt environmental policies that secure comparable opportunities for future ones —and connected it to mitigation duties, stressing that States must set ambitious emission-reduction targets guided by progressivity, equity, and common but differentiated responsibilities, in harmony with prevention under the American Convention and the San Salvador Protocol. ⁶⁶

Thus, while both Courts converge in affirming precaution as a binding element of due diligence, the IACtHR expands its scope by embedding it within a human rights framework and by linking it to principles of equity, solidarity, and intergenerational justice.

Restoration and adaptation, though traditionally treated as technical responses to environmental degradation, acquire a distinctly legal character in the recent advisory opinions. The ICJ approached adaptation through the lens of general international law and treaty obligations, treating it as an application of the customary standard of due diligence. It held that the fulfilment of adaptation obligations under the Paris Agreement must be assessed against this standard, requiring States to adopt appropriate measures capable of enhancing adaptive capacity, strengthening resilience, and reducing vulnerability to climate change, in line with the best available science. By listing ecosystem restoration, early warning systems, and resilience-enhancing infrastructure as paradigmatic measures, the Court situated restoration within the normative content of due diligence and clarified that its omission may amount to a breach of international obligations. In this way, restoration emerges in the ICJ's reasoning not merely as a policy choice, but as a legal pathway through which States discharge binding duties under both customary and treaty law. ⁶⁷

The IACtHR, while echoing the due diligence framework, reframed restoration in expressly rights-based terms. It affirmed that States must not only refrain from causing environmental harm but must also take positive measures to protect, restore, and regenerate ecosystems. These obligations are informed by the best available science as well as traditional and Indigenous knowledge, and are guided by principles of non-regression, equity, and procedural guarantees. Unlike the ICJ's inter-State orientation, the IACtHR situates restoration as a structural obligation of prevention and adaptation owed directly to individuals and communities under the American Convention. Restoration thereby becomes both a human rights remedy and a guarantee of non-repetition in the climate context. ⁶⁸

The two conceptions illustrate how international law is evolving at both universal and regional levels. The ICJ consolidates restoration as a component of due diligence within general international law, embedding it in treaty-based climate governance. The IACtHR expands its scope, reinterpreting restoration as a transformative obligation anchored in human rights law.

Justice and Differentiation

Equity, CBDR-RC, and non-discrimination exemplify the courts’ shared concern with justice in climate governance. The ICJ explicitly recognized equity as principle of international law relevant to the interpretation and application of States’ climate obligations. In that context, stressed the importance of intergenerational equity, underscoring that obligations under international law must be interpreted in light of the need to safeguard the interests of future generations when addressing climate change. ⁶⁹

The IACtHR, by contrast, embedded equity directly within the Inter-American human rights system. It placed equity alongside precaution, prevention, and CBDR-RC as guiding principles for interpreting climate obligations. Beyond distributive fairness among States, the Court reframed equity as a principle of social and climate justice: it requires targeted cooperation to address poverty and vulnerability, guides the definition of mitigation targets under progressivity and CBDR-RC, and grounds the duty to establish international funds for climate-induced mobility. The Court also extended equity to the procedural sphere, requiring inclusive and proportional access to information, participation, and justice in environmental decision-making. ⁷⁰

In other words, the ICJ consolidates equity as a principle of general international law, mediating between universality and differentiation in the distribution of climate obligations. The IACtHR, conversely, expands equity into a multidimensional principle—distributive, social, and intergenerational—anchored in the protection of human rights. While the ICJ provides a universal baseline of fairness among States, the IACtHR enriches its normative content by linking equity to justice both within and across societies. Importantly, the latter Court also connects equity to intra- and intergenerational justice—a dimension that will be examined in greater detail below.

Regarding the principle of common but differentiated responsibilities and respective capabilities (CBDR-RC) in international climate law, ⁷¹ both Courts confirm its centrality, yet they articulate its scope through distinct normative lenses. For the ICJ, CBDR-RC operates primarily as a contextual parameter of due diligence. The Court emphasized that the standard of conduct under the obligation of prevention is modulated by States’ differentiated responsibilities and capacities. Due diligence, it held, requires States to engage with and apply the best available scientific knowledge when assessing climate risks. This creates a binding expectation that all States will act upon climate science. At the same time, the Court introduced an important qualification: where a State genuinely lacks the resources to access or apply such scientific information, its failure may not necessarily constitute a breach. CBDR-RC thus modulates the scope of obligations by calibrating what can reasonably be expected of each State. The ICJ extended this reasoning to cooperation, noting that achieving global mitigation goals requires joint action by all States, but with varying levels of responsibility reflecting CBDR-RC. In this framing, CBDR-RC consolidates its place as a general principle of international environmental law, guiding interpretation of treaty regimes and the application of customary rules without creating autonomous obligations. ⁷²

For its part, the IACtHR gave CBDR-RC a more justice-oriented orientation, listing it among the core principles of the climate emergency together with precaution, prevention, equity, and cooperation. Preventive obligations, it stressed, bind all States, but their scope and costs must be interpreted considering differentiated capacities and circumstances. This distributive dimension was developed most clearly in relation to adaptation finance: relying on UNEP's findings, the Court noted that loan-based practices shift disproportionate burdens onto developing States despite their minimal historical responsibility, a situation it deemed incompatible with both CBDR-RC and the polluter pays principle. It therefore called for reforms of multilateral finance to provide concessional and grant-based support. ⁷³

The Court also applied CBDR-RC to mitigation, requiring that emission-reduction targets be defined with reference to differentiation and progressivity, demanding more ambitious action from States with greater capacity and historical responsibility, consistent with precaution and prevention. At the same time, it linked CBDR-RC to the duty of cooperation, interpreted as a principle of solidarity that requires differentiated contributions to protect human rights under climate stress, and tied it to intra- and intergenerational equity, ensuring fairness both among States and across societies. Finally, the Court extended CBDR-RC to the context of climate-induced displacement, stressing that the international community must establish and operationalize funds based on equity, solidarity, and differentiated responsibilities to support the most vulnerable States and populations. ⁷⁴

Consequently, the ICJ seems to consolidate CBDR-RC as a principle of general international law, calibrating due diligence obligations according to differentiated capabilities while preserving the universality of the prevention duty. In contrast, within the Inter-American system, CBDR-RC appears to evolve from a distributive principle of international environmental law into a vehicle for climate justice, directly linked to human rights protection.

Integration of Economy and Environment

The treatment of sustainable development by the ICJ and the IACtHR illustrates both a shared understanding of its centrality in climate governance and a divergence in its normative effects. Both Courts recognize that sustainable development is no longer a mere policy aspiration but a principle with legal consequences for how States must balance environmental protection and development.

The ICJ reaffirmed its classic definition in Gabčíkovo-Nagymaros, describing sustainable development as the “need to reconcile economic development with protection of the environment. ⁷⁵ ” In its climate change Advisory Opinion in 2025, the Court emphasized that the principle has gained “continuous and uncontested universal recognition” across treaties such as the UNFCCC, the Kyoto Protocol, and the Paris Agreement, as well as in the Rio Declaration and the Sustainable Development Goals. On that basis, the Court considered sustainable development a guiding principle of general international law, with interpretative value in clarifying the scope of customary duties such as the prevention of significant harm and the obligation to co-operate for environmental protection. ⁷⁶ In this sense, the ICJ assigns sustainable development a stabilizing role: it ensures that environmental and economic objectives are integrated into decision-making, but it does not itself generate autonomous obligations beyond shaping the content of existing ones. ⁷⁷

The IACtHR, conversely, placed sustainable development at the centre of its reasoning, treating it simultaneously as a means and an obligation for the protection of human rights and the environment. Building on the UNFCCC, the 2030 Agenda, and its own jurisprudence, the Court emphasized that effective climate action requires not only mitigation, adaptation, and reparation, but also structural transformations aimed at resilience, understood as reducing risks without compromising long-term rights, peace, and well-being. Sustainable development was defined as a process of constant improvement of human well-being, inseparable from human rights protection and environmental integrity, where economic growth is conceived not as an end but as a means conditioned by ecological limits and distributive justice. ⁷⁸

Within this framework, the Court stressed that States have an immediate obligation to adopt sustainable development strategies, even if their full implementation is progressive, and that unjustified setbacks in environmental or social protection may constitute violations of the non-regression principle. It further identified poverty and inequality as structural obstacles, requiring States to eradicate them progressively through inclusive policies, and linked this duty to the principles of equity, cooperation, and differentiated responsibilities. Procedural rights—access to information, participation, and justice—were also deemed integral, under instruments such as the Escazú Agreement, which the Court considered indispensable for “environmental democracy” and the realization of sustainable development. ⁷⁹

In this reading, sustainable development operates not merely as a programmatic goal but as an enforceable principle of the Inter-American system, guiding climate action, poverty eradication, resilience, and rights protection within a single normative framework.

Taken together, these positions reveal both convergence and divergence. Convergence lies in the recognition of sustainable development as a principle with legal weight that integrates environmental protection and development. Divergence arises in its normative function: for the ICJ, it is an interpretative tool within general international law that guides prevention and co-operation, while for the IACtHR it is also an actionable standard, inseparably tied to the protection of human rights, requiring immediate implementation, progressivity, and non-regression. The ICJ thus preserves a baseline of systemic coherence, whereas the IACtHR advances a justice-oriented paradigm that transforms sustainable development into a concrete obligation of States. This dual jurisprudence illustrates the principle's versatility: it can serve both as a universal interpretative canon and as a rights-based benchmark.

The polluter pays principle illustrates perhaps the sharpest divergence between the ICJ and the IACtHR in their treatment of interpretative principles. The ICJ acknowledged it in various treaty regimes, including the UNFCCC and the Paris Agreement, as well as in broader State practice. It observed that the principle is often invoked as a policy tool to allocate the costs of mitigation and adaptation among States and private actors and characterized it as an instrument that informs treaty interpretation and the design of domestic and international policies. ⁸⁰ In this respect, the ICJ's approach reflects its general caution in elevating policy-oriented concepts into law: while polluter pays can support the operationalization of due diligence or cooperation duties, it does not create new obligations under general international law.

Instead, the IACtHR advanced a more ambitious reading that moves the principle closer to juridification. In effect, the Court explicitly linked the polluter pays principle to accountability and reparation for victims of climate harms, arguing, as it was mentioned above, that financing mechanisms based primarily on loans to developing States undermine both polluter pays and CBDR-RC by shifting the burden onto those least responsible for emissions. ⁸¹ In this way, the Court projected the principle into the human rights domain: it not only requires polluters to bear the costs of environmental harm but also obliges States to ensure that financial structures and climate policies do not perpetuate inequities or exacerbate climate injustice. In this sense, the Court emphasized that placing disproportionate costs of adaptation on vulnerable States and communities not only contradicts the polluter pays principle but also constitutes a violation of human rights obligations under the American Convention. ⁸²

Beyond finance, the Court extended the principle to corporate accountability, requiring States to regulate companies under their jurisdiction so that they implement climate and human rights due diligence, disclose emissions, avoid greenwashing, and exercise responsibility across their value chains. ⁸³ It also tied the principle to reparations and guarantees of non-repetition, noting that polluters—whether public or private—must contribute to restoration, conservation, and resilience measures, including reparative actions for communities disproportionately affected by climate change. ⁸⁴ In sum, the IACtHR reframed the polluter pays principle as a human rights norm, expanding it from a classic tool of environmental liability into an instrument of climate justice that ensures the costs of the climate crisis are borne by those responsible for its causes rather than the most vulnerable.

Recognition of the Right to a Clean, Healthy & Sustainable Environment

Both the ICJ and the IACtHR have now positioned climate change within the framework of international human rights law, but they do so with differing emphases and levels of normative expansion. The ICJ began by affirming that States are bound to respect, protect, and ensure the enjoyment of human rights in the face of climate-related harms. Recalling its dictum in Legality of the Threat or Use of Nuclear Weapons, ⁸⁵ it recognized that the environment constitutes the “foundation for human life”. Building on this premise, the Court detailed how anthropogenic greenhouse gas emissions undermine a broad range of rights—life, health, food, water, housing, privacy, family, and cultural rights—with particular consequences for vulnerable groups such as women, children, and Indigenous peoples. In this context, it extended the principle of non-refoulement to climate displacement, prohibiting returns where climate conditions would create a real risk of irreparable harm to life. ⁸⁶

From these foundations, the ICJ recognized the right to a clean, healthy, and sustainable environment (R2CHE) as inherent in the enjoyment of other rights. It traced the emergence of this right from UNGA resolutions, the Stockholm Declaration, and regional instruments such as the Protocol of San Salvador and the African Charter. For the ICJ, the R2CHE is not an autonomous or directly justiciable right under general international law, but rather an interpretive baseline channelling existing obligations under human rights treaties and customary law. ⁸⁷

A key dimension of the ICJ's reasoning lies in the extraterritorial scope of human rights obligations. Recalling its Wall Advisory Opinion, the Court affirmed that Article 2(1) of the ICCPR extends to acts outside national territory where individuals are subject to a state's jurisdiction. This acknowledgment allows human rights obligations to apply to transboundary climate harms. Consequently, the Court required States to adopt mitigation and adaptation measures, enact legislation, regulate private actors, and integrate their obligations under human rights law, climate treaties, and customary international law in a mutually reinforcing manner. ⁸⁸

The IACtHR followed a parallel path but expanded its normative scope. Like the ICJ, it identified climate change as a direct threat to a wide range of rights. However, under Article 26 of the American Convention and Article 11 of the Protocol of San Salvador, it went further by recognizing the autonomous right to a healthy environment, conceived as both an individual and collective entitlement. ⁸⁹ Importantly, the Court affirmed that the right to a healthy environment protects not only human beings but also nature itself as a legal interest, even in the absence of demonstrable harm to individuals. This eco-centric approach, reinforced by comparative jurisprudence and instruments such as the World Charter for Nature and the Convention on Biological Diversity, reflects an evolutionary interpretation consistent with the progressive development of international human rights law. The recognition of nature as a subject of rights embodies the principle of interdependence between human rights and environmental protection, in line with structural principles of international environmental law such as intergenerational equity, precaution, and prevention. ⁹⁰

In addition to affirming interdependence between human rights and environmental protection, the IACtHR introduced several innovations. It prohibited regressivity in environmental protections, obliging States to refrain from adopting measures that would weaken safeguards against climate harms. It further required States to organize their entire apparatus, both domestically and internationally, to protect rights threatened by the climate emergency. In a decisive step beyond the ICJ, the Court declared the prohibition of irreversible climate damage a peremptory norm of international law (jus cogens). ⁹¹

The extraterritorial dimension also received a more robust treatment. While the ICJ limited itself to affirming that jurisdiction under human rights treaties can extend beyond borders, the IACtHR directly linked obligations to the principle of no transboundary harm. It held that States of origin exercise jurisdiction over activities under their control even when harmful effects occur abroad, thereby assuming responsibility for rights violations caused by cross-border environmental impacts. ⁹²

Perhaps most distinctively, the IACtHR articulated the right to a healthy climate system as a specific corollary of the right to a healthy environment. Recognizing the climate system as an essential part of the environment, the Court emphasized that its protection must be treated as a distinct legal objective, given its global functions and the existential risks posed by anthropogenic interference. It described this right in both its collective dimension—protecting the shared interests of present and future generations and of nature itself—and its individual dimension, ensuring that each person can live in a climate system free from dangerous interference. ⁹³

Finally, while the ICJ referred mainly to rights such as life, health, housing, and food, the IACtHR broadened the catalogue of affected rights to include culture, education, work, and social security. It also reinforced the procedural dimension of environmental rights, requiring guarantees of access to information, participation, and justice, together with the recognition of the right to science and Indigenous and local knowledge. ⁹⁴

In sum, while the ICJ frames the R2CHE as an essential precondition for the enjoyment of other human rights, channelled through existing treaty and customary obligations, the IACtHR conceives it as an autonomous right under the American Convention and the Protocol of San Salvador. It goes further by developing an explicitly eco-centric dimension, affirming the intrinsic value of nature as a legal interest in itself; by recognizing the right to a healthy climate as a substantive component of the right to a healthy environment, with both individual and collective dimensions; by anchoring climate protection within the hierarchy of jus cogens norms through the peremptory prohibition of irreversible climate damage; and by innovating with the integration of procedural rights into the architecture of climate governance.

Erga Omnes and Jus Cogens Obligations

The preceding analysis has examined the substantive principles governing States’ conduct—both customary and interpretative—as well as the recognition of the rights to a healthy environment and to a stable climate. Yet the legal inquiry does not end with the content of obligations. Equally central is the question of to whom these obligations are owed and with what normative authority they operate. On this point, both advisory opinions make significant contributions. The ICJ situates climate-related duties within the framework of erga omnes and erga omnes partes obligations, reaffirming their binding nature under customary and treaty law, and emphasizing that their fulfilment must consider the interests of both present and future generations. The IACtHR, for its part, broadens the circle of beneficiaries to include individuals, vulnerable groups, future generations, and even nature itself, while elevating certain environmental duties—such as the prohibition of irreversible climate harm—to the rank of jus cogens. It is to this broader dimension—the beneficiaries, scope, and hierarchy of climate obligations—that the following section now turns.

Climate Responsibility: From States to the International Community

Adopting a state-centred legal method, the ICJ first identifies the primary rules that bind States in the climate context and then sets out the legal consequences that follow from breach. On scope, the Court makes plain that the General Assembly asked it to address the obligations of States, but the material reach of those obligations extends to “the full range of human activities” that contribute to climate change; accordingly, States must regulate and supervise non-State actors within their jurisdiction or effective control where their activities result in adverse climate effects. ⁹⁵

On whom is affected, the Court acknowledges differentiated exposure—especially small island developing States—yet stresses that the secondary rules of responsibility do not vary with the status of the injured State; “specially affected” or “particularly vulnerable” States are, in principle, entitled to the same remedies as any other injured State. ⁹⁶

Turning to the character of the obligations, the Court holds that States’ obligations “pertaining to the protection of the climate system and other parts of the environment from anthropogenic GHG emissions”—in particular, the customary duty to prevent significant transboundary harm—are obligations erga omnes; in parallel, the core mitigation/cooperation duties under the UNFCCC and Paris Agreement are obligations erga omnes partes, such that every party has a legal interest in compliance and may invoke responsibility. ⁹⁷

Against that background, the Court aligns the climate regime with the general law of State responsibility for international wrongful acts to explain who may invoke responsibility and what may be claimed. ⁹⁸ For community-interest obligations, a non-injured State may invoke responsibility under ILC Article 48, ⁹⁹ but its remedial reach is limited to cessation, assurances/guarantees of non-repetition, and the performance of reparation in the interest of the injured State or beneficiaries; it cannot claim compensation for itself. ¹⁰⁰ By contrast, an injured State (including a specially affected one) retains the full remedial bundle, subject to proof of damage and causation. ¹⁰¹

The Court then details the consequences of breach. First, if the duty of performance continues after breach: for example, a court or tribunal may require a State to align an inadequate NDC with its Paris obligations. Second, there is a duty of cessation—which may require revoking wrongful measures and employing all means at a state's disposal to reduce GHG emissions—together with appropriate assurances and guarantees of non-repetition where warranted. Third, where an injured State establishes a “sufficiently direct and certain causal nexus” between the wrongful act and the harm, it is entitled to full reparation—restitution, compensation, and/or satisfaction—determined case-by-case. The Court confirms that environmental damage is compensable “in and of itself,” including impairment or loss of environmental goods and services pending recovery; when the extent of damage cannot be precisely quantified, global-sum compensation based on equitable considerations may be awarded. Recognizing that climate harm is diffuse and cumulative, the Court underscores that causation is not impossible: it must be assessed in concreto under the Court's established standard. ¹⁰²

In sum, the ICJ consolidates a community-interest architecture for climate protection: certain customary duties (notably prevention) are erga omnes and core treaty duties are erga omnes partes, expanding standing to invoke responsibility while preserving classic injured-State remedies—continuing performance, cessation/non-repetition, and full reparation upon proof of a sufficient causal nexus. The opinion thus binds States to control private conduct within their jurisdiction or effective control and equips both injured and non-injured States with differentiated remedial pathways suited to the diffuse nature of climate harm.

By contrast, the IACtHR recasts climate duties as obligations correlating directly with rights-holders. It grounds an enhanced standard of due diligence in the State's obligation to guarantee rights, extending prevention into the private sphere and requiring proactive, science-based measures. It then articulates two doctrinal determinations with systemic consequences for third-party standing and community interests: first, it affirms the existence in international environmental law of an obligation erga omnes not to cause transboundary environmental damage; second, it recognizes—by majority—a peremptory (jus cogens) prohibition on anthropogenic conduct that risks irreversible harm to the vital equilibrium of ecosystems, ¹⁰³ a hierarchy that, by its nature, generates obligations toward all. In operational terms, the Court requires States to legislate and enforce corporate climate due diligence across the entire value chain, mandate disclosure of value-chain GHG emissions, adopt measures against greenwashing and undue influence, and strictly supervise high-risk activities—making explicit the private-sector reach of State obligations. ¹⁰⁴

It is worth to mention that the Court's jus cogens conclusion rests on a progressive crystallization of environmental obligations: precaution, polluter-pays, the erga omnes duty not to cause transboundary environmental harm, sectoral treaties on climate, pollution and biodiversity, the rise of intergenerational equity, and efforts to penalize conduct that causes massive and lasting ecosystem damage—all pointing to a core of norms that admit no agreement to the contrary where irreversible harm to life-supporting ecosystems is at stake ¹⁰⁵ .

The IACtHR argues that protecting the planetary life-support system is a necessary precondition for the enjoyment of fundamental rights (principle of effectiveness); that rights to life, integrity, health, and non-discrimination depend on maintaining the ecosystem's vital equilibrium; that a broad consensus has emerged through multilateral environmental law, UNGA practice, and comparative jurisprudence; and that the peremptory prohibition does not conflict with positive law. ¹⁰⁶

Read together, these considerations support the non-derogable status of a prohibition on massive, irreversible environmental harm and a correlative duty of all States to cooperate to end such conduct. To reinforce this point, the Court resorts to an a contrario sensu argument: if anthropogenic conduct that irreversibly disrupts the ecosystem's vital equilibrium were not imperatively prohibited, the sine qua non conditions for the effectiveness of fundamental human rights—already protected at the highest normative rank—would be undermined; accordingly, the obligation to preserve that equilibrium must be construed as a peremptory duty under international law. ¹⁰⁷

It bears noting that the IACtHR situates its jus cogens finding particularly within its regional context marked by dense acceptance and practice around a right to a healthy environment and a science-responsive duty of prevention, which gives that characterization real traction within the Inter-American system. ¹⁰⁸

Individuals, Communities, Vulnerable Groups and Intergenerational Equity

Having identified the approaches taken by the ICJ and the IACtHR in their respective advisory opinions, it seems almost obvious the margin of manoeuvre that individuals, communities and vulnerable groups have to safeguard their human rights in the context of climate emergence. Both advisory opinions reposition climate harm through human rights law, but they do so with different legal grammars that matter for who is protected and how. Before entering general conclusions, it is relevant to mention, in this sense, common points of the two opinions:

First, both courts affirm that environmental integrity is a condition for the enjoyment of a range of human rights (life, health, an adequate standard of living, privacy, family and home). From that premise, climate impacts—sea-level rise, extreme heat, drought and desertification, intensified disasters—are not merely ecological phenomena but rights-relevant injuries borne by concrete persons and communities. The opinions therefore treat individuals and communities as beneficiaries of climate-related protection, even when the pathways to vindication differ institutionally. ¹⁰⁹

Second, both courts take vulnerability seriously, but the Inter-American opinion develops it most fully. It identifies groups that experience disproportionate burdens—Indigenous peoples, Afro-descendant and peasant communities, women and children, persons living in poverty, persons with disabilities, older persons, migrants and environmental defenders—and links their protection to tailored State conduct (for example, by requiring barrier-removal and inclusive decision-making). The ICJ acknowledges differentiated exposure (including peoples whose territories are at existential risk) and connects climate degradation to the impairment of specific rights, but it leaves the fine-grained catalogue of vulnerable groups, and the remedies that track their needs, to the relevant human-rights regimes and domestic implementation. ¹¹⁰

Third, procedural guarantees are treated not as afterthoughts but as the means by which those affected can influence choices that determine their survival and dignity. Access to information and science, public participation in decision-making, and access to justice are framed as essential conditions for effective protection. The Inter-American opinion embeds these guarantees as justiciable entitlements within its regional system; the ICJ locates them within the applicable treaty frameworks and practice and emphasizes their functional role in making rights protection real. In practical terms, this convergence means climate policy that bypasses disclosure, participation, and remedy channels risks being legally deficient even before one assesses its substantive ambition. ¹¹¹

Fourth, both opinions speak to human mobility. They recognize that climate-related conditions can endanger life and health to a point that engages non-refoulement, thereby constraining removal or return where a real risk of irreparable harm exists. This matters for individuals and communities already on the move, and for those facing foreseeable displacement as climatic baselines shift. ¹¹²

Fifth, intergenerational equity operates in each opinion, but at different normative levels. The ICJ treats it as an interpretive principle: present generations are trustees of humanity and must consider the long-term implications of their choices for those yet to be born. It guides the reading and application of existing rules but does not, in that forum, become a free-standing right. The Inter-American opinion goes further, integrating inter- and intragenerational equity into rights analysis and requiring that preventive, restorative, and regenerative measures be designed with explicit regard to future generations and to fair distribution of burdens and benefits within the present one. ¹¹³ The upshot is that long-horizon impacts are not merely a policy consideration; they are part of the legal assessment of whether measures respect and guarantee protected interests. In effect, the IACtHR elevated them into the domain of human rights, directly enforceable under the American Convention. ¹¹⁴

Specifically, the IACtHR's reference to intra- and intergenerational equity provides an interpretive bridge to identifying the beneficiaries of its reasoning. On the one hand, the principle of intragenerational equity underscores that individuals and communities currently facing disproportionate burdens from climate change—such as Indigenous peoples, Afro-descendant and peasant communities, women, children, persons with disabilities, people living in poverty, and environmental defenders—are immediate rights-holders entitled to protection and participation. ¹¹⁵ Their recognition as beneficiaries reflects the Court's concern for distributive justice within the present generation. On the other hand, the principle of intergenerational equity extends the circle of beneficiaries beyond the living, affirming that future generations are legitimate rights-holders of a healthy environment and, in the Inter-American framing, of a healthy climate. ¹¹⁶

Taken together, it is possible to conclude that individuals and communities are not abstract addressees but concrete bearers of interests whose protection depends on environmental conditions. Vulnerable groups are entitled to heightened attention, not only because they suffer more, but because law requires the removal of structural barriers that keep them from shaping the responses that affect them most. Procedural guarantees are the operational core that turns protection from paper to practice. And intergenerational equity supplies the temporal dimension: today's choices are legally relevant because they condition the possibility of dignified life tomorrow. Particularly on this last point, it could be said that both courts recognized future generations as beneficiaries, but with different legal force.

Now, analysing their differences, since the ICJ centres all its efforts in trying to determine States obligation in this matter and their legal consequences when there are not fulfil, its analysis on human rights is basically from the perspective of the State. Individuals and communities emerge then as indirect beneficiaries of the Court's reasoning: their protection is secured primarily through the prism of state obligations, insofar as states are required to take measures that safeguard human rights by ensuring the integrity of the climate system. Indeed, the entitlement of individuals to hold states accountable for failures regarding climate obligations is contingent on procedural and substantive provisions established in particular treaties or legal instruments, not on customary principles alone. ¹¹⁷

The principal limit is institutional: the ICJ deliberately does not create new international standing for individuals or for groups in situations of vulnerability; their direct access depends on the design of specific treaties and on their domestic implementation. Likewise, although the Court recognizes vulnerabilities particular to certain groups (e.g., women, children, Indigenous peoples) and non-refoulement risks linked to climate harms, concrete remedies for individuals will generally proceed through domestic avenues or treaty-based procedures rather than the inter-State responsibility track. From a protection perspective, this appears to maintain a conservative posture that preserves the coherence of the legal architecture, while shifting to States the burden of legislating, regulating private actors, and operationalizing channels for participation, access to information, and access to justice, so that individuals and vulnerable groups can effectively vindicate their rights in the face of climate risks.

Finally, concerning intergenerational equity, the ICJ affirmed that the present generation holds the climate system “in trust for humanity,” requiring States to safeguard and transmit it under conditions that ensure dignified living. Here, intergenerational equity functions as an interpretive principle of customary and treaty law, guiding prevention, cooperation, and equitable distribution of burdens across societies. The IACtHR, however, elevates intergenerational equity into the domain of enforceable human rights. It declares that the right to a healthy environment (and, within it, a healthy climate) is owed “to present and future generations,” and requires that duties of prevention, restoration, and regeneration be explicitly designed with reference to future generations—transforming intergenerational equity from a principle into a binding legal obligation under regional law.

Fragmentation or Complementarity?

Determining whether both advisory opinions represent an instance of fragmentation or, conversely, of complementarity within international law is far from straightforward. On one hand, their coexistence may be viewed as a manifestation of fragmentation, insofar as it risks generating divergent jurisprudence and legal uncertainty. On the other hand, it may also be seen as a form of complementarity, whereby distinct judicial interpretations enrich the understanding of international law by providing multiple yet plausible reconcilable perspectives within an increasingly pluralistic legal order.

From an institutional standpoint, what is at stake is the coexistence of two international judicial bodies examining the same phenomenon through distinct hermeneutical frameworks. ¹¹⁸ From a normative perspective, the issue of fragmentation largely hinges on whether International Human Rights Law (IHRL) is conceived as an integral part of general international law or alternatively, as a lex specialis or autonomous regime operating within. ¹¹⁹ If conceived in either of the latter senses ¹²⁰ , the ICJ's state-centred reasoning could be perceived as fragmentary when contrasted with the rights-centred interpretive method employed by the IACtHR. ¹²¹

It is relevant to note that the ICJ's Advisory Opinion under analysis was delivered two months after that of the IACtHR. The temporal sequence is significant: the ICJ had the opportunity to consider the Inter-American Court's reasoning and, to some extent, to anticipate potential interpretive divergences. In this regard, the ICJ's formulation of the relationship between human rights and environmental protection can be seen as an intentional step toward preventing fragmentation. The Court expressly recognized that “[t]he right to a clean, healthy and sustainable environment results from the interdependence between human rights and the protection of the environment. Consequently, in so far as States parties to human rights treaties are required to guarantee the effective enjoyment of such rights, it is difficult to see how these obligations can be fulfilled without at the same time ensuring the protection of the right to a clean, healthy and sustainable environment as a human right. The human right to a clean, healthy and sustainable environment is therefore inherent in the enjoyment of other human rights. The Court thus concludes that, under international law, the human right to a clean, healthy and sustainable environment is essential for the enjoyment of other human rights.” ¹²² By explicitly framing the right to a clean, healthy, and sustainable environment as both derivative of and essential to the realization of other human rights, the ICJ moved closer to the rights-centred logic advanced by the IACtHR, thereby signalling a deliberate convergence rather than a jurisdictional divide.

Consequently, rather than evidencing fragmentation, both advisory opinions stand as complementary milestones in the juridification of the climate crisis within contemporary international law. While the ICJ clarifies and systematizes the existing general legal framework, the IACtHR adopts an evolutive approach that advances its normative development. Their interaction reveals a growing convergence toward a collective legal response to global environmental degradation.

Indeed, the ICJ's 2025 Advisory Opinion represents a landmark in grounding climate change within the body of general international law, affirming the binding character of States’ obligations of mitigation, adaptation, and cooperation under customary and treaty law, and clarifying their erga omnes nature. By recognizing the right to a clean, healthy, and sustainable environment as “essential for the enjoyment of other human rights” and by explicitly linking it to the principle of due diligence, the Court endowed this right with unprecedented systemic legitimacy and universality. The IACtHR, in turn, has been instrumental in advancing the humanization and deepening of environmental law. Through its teleological and pro persona interpretation, it not only elevated environmental protection to the status of an autonomous and justiciable human right but also explicitly articulated the right to a healthy climate as a distinct entitlement derived from the American Convention and the San Salvador Protocol. Going further, the Court characterized the prohibition of irreversible climate and environmental harm as a norm of jus cogens, reasoning that ecological stability constitutes a precondition for the exercise of rights already recognized at the highest level of international law.

The above doctrinal innovation redefines environmental protection as part of the international community's peremptory legal order. Moreover, the IACtHR operationalized these principles by defining the content of States’ positive duties—prevention, restoration, cooperation, and enhanced due diligence—within a human rights framework, thereby providing concrete guidance for domestic implementation. Taken together, the ICJ's achievement lies in institutionalizing the global legal foundation of climate obligations, while the IACtHR's contribution consists in humanizing, expanding, and hierarchizing them. The result could be seemed like a complementary articulation of universality and specificity: the ICJ ensures coherence and authority at the systemic level, while the IACtHR translates and enriches these global norms through a rights-based, hierarchical, and future-oriented approach that links international responsibility to human dignity, intergenerational equity, and environmental justice.

Notwithstanding the foregoing, and given that each court operates within its own jurisdictional and normative sphere, it is legitimate to question whether the recognition of nature as a subject of rights, the articulation of an autonomous right to a healthy climate, and the elevation of the prohibition of irreversible climate harm to the status of jus cogens can genuinely operate as a complementary framework between the universal and regional legal systems. Yet, it must also be acknowledged that international law itself emerges from the interaction of diverse legal systems and conceptions of law—both its source of richness and its inherent fragility. In this regard, Dupuy's observation remains particularly relevant: “[A]n international legal order can only exist as long as it guarantees to its subjects a unity which is sufficiently organic and substantial to serve as an effective framework for their international relations.” ¹²³ This notion of organic unity suggests that coherence in international law does not rest on uniformity, but rather on its capacity to integrate diversity—allowing different judicial voices, methodologies, and regional experiences to converge toward shared principles that preserve both systemic unity and normative dynamism.

From this perspective, the IACtHR's normative innovations should not be interpreted as acts of fragmentation but rather as catalysts for the progressive development of international law. Even if not yet endorsed by the ICJ or reflected in uniform State practice worldwide, such regional innovations may gradually shape the contours of universal acceptance through processes of normative diffusion and cross-referential reasoning. Ideally, the interaction between the two courts should evolve into a form of cooperative judicial pluralism—a dynamic interplay in which regional creativity and universal authority converge toward shared foundational values. Such progress could unfold much as it has in the past, when developments in international human rights law progressively influenced general international law in areas that today seem self-evident—such as the recognition of new subjects of law, the expansion of sources, the articulation of international responsibility, and even the understanding of the Security Council's functions, among others. ¹²⁴ The result would be a progressive normative evolution of international law, pointing toward a more articulated legal landscape where environmental integrity and human rights coexist in dynamic interaction, informed by science.

Conclusion

At the foundation of both advisory opinions lies a philosophical divergence. The ICJ embodies a positivist orientation, faithful to its role of clarifying and systematizing existing law through methodological prudence and doctrinal stability. The IACtHR, by contrast, adopts a teleological or natural law vision, interpreting norms through the lens of justice and human dignity. These two traditions—one consolidating, the other transformative—reflect the enduring dialectic between legal certainty and moral progress that animates international jurisprudence.

The ICJ's approach reveals an effort to balance caution with adaptability—preserving doctrinal continuity while recognizing the cross-regime interactions required for an effective legal response to the climate crisis. This prudence enhances predictability and coherence within the international legal order but also limits the Court's capacity to respond at some point to the normative challenges of the climate emergency. ¹²⁵ The IACtHR, by contrast, privileges justice and innovation, employing an evolutive interpretation to connect environmental protection directly to the realization of human rights. In doing so, it broadens the moral and legal scope of State obligations while accepting the risk inherent in normative expansion.

The resulting frameworks differ in depth and reach. The ICJ offers a universal foundation grounded in general international law, while the IACtHR provides a regional, right-centred approach that brings legal obligations closer to scientific facts, societal realities, and policy responses – particularly in addressing the asymmetries that constrain developing States ¹²⁶ , such as limited access to finance and technology. The challenge ahead lies in ensuring that legal coherence does not come at the expense of justice or equity.

Both opinions also share an epistemic dimension: their reliance on the findings of the Intergovernmental Panel on Climate Change (IPCC) represents an unprecedented integration of law, science, and policy. Geopolitically, this reliance reveals a deeper dynamic: climate law is shaped not only by States and treaties but also by knowledge-producing institutions that mediate global power. The heavy reliance of both Courts on IPCC assessments confirms that science has become the evidentiary backbone of international climate law. Yet because such science is itself a negotiated product, judicial reliance on it simultaneously strengthens the authority of law and risks constraining its normative evolution within the limits of politically filtered knowledge.

Ultimately, the ICJ's positivist restraint and the IACtHR's natural law dynamism could be seen as opposing paradigms but complementary expressions of the international community's evolving legal conscience. Their juxtaposition exemplifies a form of productive pluralism—a convergence of methods and philosophies directed toward a shared goal: the juridical protection of humanity and the planet. In this convergence lies the embryo of a corpus iuris climatis: a plural yet plausible coherent legal order grounded in the interdependence of environmental integrity, human dignity, and intergenerational justice.