Symposium on Advisory Opinion AO-32/25 on the Climate Emergency and Human Rights: The Principle of Common but Differentiated Responsibilities

[Lucas Carlos Lima is professor of international law at Universidade Federal de Minas Gerais and coordinator of the Brazilian Researchgroup on international courts and tribunals]

The Advisory Opinion on the Climate Emergency and Human Rights (OC-32/25), rendered by the Inter-American Court of Human Rights (IACtHR or Court) on 29 May 2025, offers a contribution to clarifying the relationship between international environmental law and international human rights law. One key point of intersection lies in whether, and how, foundational principles of international climate law , chief among them the principle of common but differentiated responsibilities and respective capabilities (CBDR-RC),  inform States’ human-rights obligations.

CBDR-RC, canonically framed in Principle 7 of the 1992 Rio Declaration and embedded across the climate regime, allocates greater burdens to States with larger historical contributions and greater capacities. Read one way, the principle functions as an equity device within mitigation, adaptation, and finance. Read another, it can be deployed to justify narrower or slower-moving obligations. When transposed from climate law into the register of human-rights duties, that second reading looms large: differentiation may become a way to temper, sequence, or even skirt performance otherwise cast in universal terms.

In this post, I examine how the Court engaged with CBDR-RC in OC-32/25. I argue that, while the Court acknowledged the principle’s relevance to State obligations under international climate law, it fell short of articulating a clear vision of its normative implications within the realm of human-rights obligations. The result is a cautious incorporation – recognition without full elaboration – leaving open some questions about how differentiation might operate in a system premised on the universality and indivisibility of rights. 

Invoking the CBDR-RC principle: the position of States. 

As argued elsewhere, it is unsurprising that States taking part in the advisory proceedings leaned heavily on CBDR-RC. Chile and Colombia referenced the principle in the request, and most participating States invoked it in their written or oral submissions. Paraguay addressed CBDR-RC as a guiding interpretive principle, urging the Court to factor economic capacity into any articulation of duties. El Salvador underscored that “all States” share responsibility, but that burdens must be commensurate with historical and current contributions as well as technological and economic capability. Barbados was explicit that developed States must “do more” in practice. Mexico went further, rooting differentiation in Article 26’s duty of cooperation under the American Convention. Brazil offered perhaps the clearest construction: any clarification of human-rights-related climate obligations should take CBDR-RC seriously by acknowledging Latin America’s proportionally smaller historical emissions, heightened vulnerability, and acute needs for capacity-building, finance, and technology transfer. 

The legal tension is evident. Most parties to the American Convention are developing States; an advisory opinion cannot bind non-parties in the Global North. What role, then, can historical responsibility and capacity play in interpreting obligations under a regional human-rights treaty whose addressees are, for present purposes, similarly situated? Chile flagged this nuance. That framing suggests a more limited,but not negligible,  place for differentiation in the Inter-American context: less a license to dilute rights than a criterion for calibrating cooperation, progressive realization, and the means of implementation. It is precisely in that narrow space that the Court’s cautious engagement in OC-32/25 leaves important questions open, such as how the principle may mitigate the human rights obligations of a given State Party to the Convention. I will address this question in the final section of the text.

Recognizing the CBDR-RC principle: the Court’s general approach

The Court is explicit about the principles that will guide its interpretive task. In paragraph 216, it lists both human-rights canons and climate-law fundamentals, placing CBDR alongside them:

“…the task of interpretation with which this Court has been entrusted on this occasion will be undertaken under the guidance not only of the principles inherent in the international protection of human rights, such as the pro persona principle, the best interests of the child, the principle of progressivity, and the prohibition of discrimination; but also, taking into consideration fundamental principles and obligations in the context of the climate emergency such as the pro natura principle, the precautionary and prevention principles, the polluter-pays principle, intra- and inter-generational equity, common but differentiated responsibilities, the obligation of cooperation, and the prohibition of transboundary damage.”

para. 216

The Opinion then situates CBDR-RC within the treaty context it uses as interpretive scaffolding. It notes that the Paris Agreement “reaffirmed the need to act in accordance with the principle of common but differentiated responsibilities,” placing CBDR-RC alongside science and human-rights considerations in its framing of climate action (para. 139). It also recalls that the UNFCCC establishes both common and differentiated obligations and explicitly elevates “equity, [and] common but differentiated responsibilities and respective capabilities” as guiding principles (paras. 125–126).

CBDR-RC also appears as an interpretive lens for the duty of international cooperation. The Court links cooperation to equity and to taking into account differences, capabilities, and responsibilities among States (para. 253). It underscores that this very idea underlies the UNFCCC’s preambular call for the “widest possible cooperation… in accordance with [States’] common but differentiated responsibilities and respective capabilities” (para. 254). Most directly, the Court states that the cooperation obligation “must be interpreted in light of the principles of equity and common but differentiated responsibilities,” and that States must cooperate in good faith while taking account of differentiated responsibilities, respective capabilities (especially economic and technical), and specific needs (para. 258), clarifying that this cooperation spans all measures needed to respond to the climate emergency (para. 259).

The Court then weaves differentiation into its due-diligence analysis under human rights law. After setting an “enhanced due diligence” [devida diligencia reforzada] standard for prevention (paras. 233–236), it adds that “the scale and cost of those measures are also determined by the principle of common but differentiated responsibility, as well as by the particular circumstances of each State,” while emphasizing that the prevention obligation binds developed and developing States alike (para. 237). The Court characterizes due diligence as a variable concept that depends on circumstances and available science/technology—an idea that fits hand-in-glove with differentiation (para. 232). In short, CBDR-RC calibrates how States must fulfill preventive duties; it does not excuse whether they must. I will revert to this point later.

CBDR-RC also guides how the Court reads the Parties’ mitigation architecture under the Paris Agreement. When discussing the obligation to align NDCs with “highest possible ambition,” the Court quotes and relies on Article 4(3)’s formula – ambition “in accordance with common but differentiated responsibilities and respective capabilities, in the light of different national circumstances” – and expressly recalls that “developed countries should take the lead,” whereas developing countries are encouraged to move over time toward economy-wide targets (paras. 323–324).

Finally, the Opinion embeds CBDR-RC within its justice-and-equity filter for interpreting climate targets. In setting the normative yardstick (Paris’s 1.5°C/“well below 2°C”), the Court says this alignment must be read through fairness considerations – including the “principles of common but differentiated responsibilities,” equity, and capabilities – so that burden-sharing reflects historical contributions, resources, and national situations (paras. 327–330, 334). This is a form of indirect CBDR-RC incorporation: the temperature goal and associated State efforts are calibrated by differentiation-sensitive justice criteria.

Taken together, these references attest to a broad acceptance of the principle’s applicability in the sphere of inter-State climate obligations. It bears emphasizing, however, that the Court’s express invocations of CBDR/CBDR-RC largely accompany its survey of the climate regime, rather than the interpretation of State conduct in discharging human-rights duties. Thus, even as this recognition tracks the expectations and submissions of participating States, it also suggests that the principle’s purchase within the human-rights frame remains uncertain.

The Court’s Reasoning on CBDR-RC: Implications for Human-Rights Duties

Reading the second half of the Advisory Opinion – where the Inter-American Court steps away from its survey of the general climate regime and turns to sector-specific inter-American jurisprudence and States’ obligations under a climate emergency – one notices a marked absence of references to CBDR-RC. That silence is open to two readings.

First, it may suggest that there is little room, within this body of human-rights jurisprudence, for the kind of exceptionalism often associated with CBDR-RC. Put differently, the Court does not identify with any clarity how particular levels of development and capacity might shape compliance with Convention obligations. One might wonder whether this means that the principle has a narrow scope of application among developing States. But the IACtHR did not explicitly address this question.

A second, equally plausible reading is that the Court has left the question to be worked out in contentious litigation. On this view, differentiation could surface in focused ways: in the progressive realization of certain Article 26 obligations; in calibrating the scale, timing, and means of measures required by enhanced due diligence; and in structuring the duty to cooperate. Remedies and compliance supervision could also incorporate CBDR-sensitive criteria. Whether and how these factors may shape obligations would then be tested case by case.

What the Court does say, however, is decisive for the present: it weaves CBDR-RC’s logic into the standard of enhanced due diligence, making clear that differentiation calibrates how States must perform – not whether they are bound. In the Court’s words, “[t]he content of the due-diligence standard will depend on the specific risks that loom over each of the human rights threatened in the context of the climate emergency” (para. 234). And: “[t]he measures required to comply with this standard may vary over time, for example, based on scientific discoveries, new technologies, or the identification of new forms of risk. The breadth and costs of these measures are also determined by the principle of common but differentiated responsibilities, as well as by the particular circumstances of each State.” (para. 237).

At the same time, the Court expressly cabins the reach of differentiation: “the existence of this obligation does not depend on the level of development; that is, the obligation of prevention applies equally to developed and to developing States, without prejudice to the clarifications regarding the duty to cooperate and [CBDR-RC] to be set out below.” (para. 237). In short, CBDR-RC informs calibration (due diligence and cooperation), not derogation from human rights obligations.

In sum, the Opinion’s treatment leaves a narrow but important space in which differentiation may matter – chiefly as a criterion for calibrating performance, sequencing, and means of implementation – while signaling that core human-rights obligations remain common to all. That is a door the Court may expect future contentious cases to open carefully; it is not, however, a valve of escape.

Conclusions

The OC-32/25 recognizes – just as several participating States urged – that CBDR-RC is part of the normative backdrop against which climate-related human-rights duties are read. That recognition gives differentiation a legitimate role in the Inter-American legal dynamics. Yet precisely because the Opinion may reverberate beyond the advisory setting, uncertainty remains about how the Commission and the Court will handle the measure of exceptionalism inherent in CBDR-RC when applying (or reviewing) human-rights obligations. That uncertainty is sharpened by the Opinion’s own invitation to domestic judges to apply its standards through conventionality control (para. 560): once national courts engage with CBDR-RC in concrete controversies, the contours of any permissible differentiation will begin to harden – or to fray.

The greatest indeterminacy lies in the application of the enhanced due diligence standard. For States in the region, this is where calibration actually bites: CBDR-RC and national circumstances may influence how prevention is performed – its scale, timing, and means, including cooperation, finance, technology, and capacity-building. But the standard itself is stringent, and the burden to meet it remains high. In practice, States will have to demonstrate ambition, iterative adjustment to evolving science and risk, and verifiable metrics that can withstand Inter-American and domestic scrutiny. Differentiation may shape performance; it does not excuse non-performance.

The enduring tension will be worked out in the balance of principles the Court has assembled. On one side stand the human-rights canons – pro persona, progressivity, non-discrimination; on the other, the climate-law logics of equity, cooperation, and CBDR-RC. OC-32/25 sketches that balance without fixing it. Future litigation – both before the Inter-American organs and in domestic courts exercising conventionality control – will test where the balance settles: whether CBDR-RC functions as a principled criterion for calibration within a universal rights framework or becomes a lever for broader margins of discretion. The Opinion points toward the former, but the proof will lie in how judges and policymakers apply it to facts on the ground.

Photo attribution: Photo by lucas mendes on Unsplash