Beyond Bilateral Notification and Consultation

The 2025 ICJ Advisory Opinion on Climate Change at ¶299 holds that “notification and consultation are particularly warranted when an activity significantly affects collective efforts to address harm to the climate system, such as the implementation of policy changes in relation to the exploitation of resources linked to GHG emissions, or with respect to information that is necessary for meaningful co-operation among States to address the adverse effects resulting from GHG emissions.” It establishes that notification and consultation constitute both an independent rule of customary international law and an element of the due diligence standard. That formulation appears to extend the framework of Pulp Mills–Lac Lanoux — discrete project, identifiable affected state, bilateral notification — to global climate governance. Read with the Opinion’s broader customary framework however, ¶299 does something more structurally disruptive: it severs the procedural obligation from the bilateral scaffolding that has always underpinned it, and replaces that with a multilateral trigger the existing doctrine was not designed to support.

Three claims drive the analysis. First, the bilateral model of procedural consultation crystallised in Pulp Mills on the River Uruguay presupposes a discrete activity, an identifiable affected state, and spatially proximate harm — ¶299 disrupts all three. Second, read alongside the Opinion’s human rights section and the Inter-American Court’s near-simultaneous Advisory Opinion AO-32/25, ¶299 reveals a two-level procedural framework in which international consultation must be grounded in genuine prior domestic participation. Third, where the wrongfulness threshold at ¶427 is engaged, the procedural failure ceases to be separable from substantive due diligence breach, collapsing the distinction Pulp Mills had maintained.

Bilateral Procedure and Its Structural Limit

Procedural environmental obligations were built for a world of dyadic harm. Trail Smelter  established the customary no-harm principle, the lineage of substantive harm prevention attaching to any transboundary harm pathway. Lac Lanoux addressed a narrower and structurally distinct obligation — the lineage of procedural consultation over shared resources — requiring France to consult Spain in good faith before diverting waters of a transboundary basin. Article 8 of the ILC’s 2001 Articles on Prevention of Transboundary Harm generalised the Lac Lanoux template, requiring notification to states “likely to be affected” — proximate, identifiable neighbours facing harm via a determinable pathway.

Pulp Mills brought both lineages together over a single shared watercourse. Uruguay’s failure to notify Argentina through the CARU commission before authorising two pulp mills was an internationally wrongful act independent of any finding of harm to the river. At ¶¶71–79, the Court was deliberate in establishing that procedural and substantive obligations are independently answerable, and that a procedural breach does not automatically produce a substantive finding. That severability was coherent because both obligations ran to Argentina, concerned the same shared river, and shared the same identifiable factual subject matter — features inherited from Lac Lanoux.

It is this consultation lineage that ¶299 reconfigures. The ITLOS May 2024 Advisory Opinion had already begun pulling environmental procedural obligations away from bilateral logic, calibrating due diligence by CBDR-RC and the collective interest in preserving the shared marine medium rather than by the bilateral relationship between emitting and affected states. The ICJ aligned itself with that approach, committing to “ascribe great weight” to the Tribunal’s interpretations (¶338). Brunnée underscores the doctrinal scope of this move: the Court is now explicit that the customary harm prevention obligation is not confined to instances of direct cross-border harm. Paine reads the opinion as making due diligence “variable and evolutive” in ways calibrated to fact-specific elements rather than to bilateral relationships. The bilateral spatial assumption that scaffolded Lac Lanoux — and that Pulp Mills inherited — is the assumption ¶299 dismantles.

Three Ways ¶299 Breaks the Bilateral Framework

The first departure concerns the triggering condition. A discrete extraction project — a particular oil well, a particular coal mine — does have an identifiable start date.  ¶299’s trigger, however, is not the project itself but the moment at which an activity “significantly affects collective efforts to address harm to the climate system”. The relevant analytical unit is the policy framework that authorises serial projects: licensing rounds whose aggregate output materially shifts the global trajectory; subsidy regimes that lock in fossil capital for decades; and NDC backsliding that recalibrates downward what other states must absorb to keep 1.5°C in reach. None has a discrete start date, and none can be addressed by procedural notification designed for individual project authorisations. Voigt reads ¶299 conservatively, treating it as a project-level due diligence factor “especially warranted when planning fossil fuel extraction or combustion projects, which may affect other states’ fossil fuel phase-out policies or their transition to renewable energies.” Van Asselt and Rao capture the structural shift more directly: an interpretation of ¶299 informed by the customary duty to cooperate would, drawing on the OACPS submission, “internationalise decision-making for major fossil fuel projects, creating procedural rights for climate-vulnerable States in other nations’ energy planning.” Even on Voigt’s narrower reading, the trigger is the project’s aggregate effect on the global energy transition, not its bilateral neighbourly effect which is structurally different from what Lac Lanoux envisaged. The consultation obligation therefore operates continuously, embedded in the framework of climate policy formation rather than bolted onto individual project decisions.

The second departure is the addressee. Uruguay’s obligation in Pulp Mills ran to Argentina. The obligation in ¶299, read alongside ¶¶440–443, runs to the international community as a whole. The Court confirms that the customary obligation to prevent significant harm to the climate system is owed erga omnes, while treaty obligations are owed erga omnes partes (¶¶440–442). Paddeu and Jackson identify this as a doctrinally novel step: the Court at ¶442 explicitly cites Article 48 of the ILC Articles on State Responsibility and “for the first time explicitly acknowledged the legal standing of all States in relation to obligations erga omnes” under customary law. Since ¶299 operates simultaneously as an independent customary norm and as an element of treaty-based due diligence, both dimensions engage the collective addressee. Brunnée draws the implication for procedure specifically: given the Court’s reference to “obligations pertaining to the protection of the climate system” being erga omnes (¶440), it stands to reason that “all harm prevention obligations are owed erga omnes”, including the procedural requirements detailed by the Court. The Court at ¶357 found that sea-level rise threatens forced displacement, territorial integrity, and permanent sovereignty over natural resources in ways closely connected to the right of self-determination, bringing states like Vanuatu, Tuvalu and Bangladesh into the frame as legal interest-holders whose own emissions are negligible relative to the global total (see further Comar). Consultation owed to the international community as a whole is not consultation owed to everyone in the abstract — it is consultation owed to a community whose most vulnerable members have the most acute legal stake in its discharge.

The third departure is spatial. Bilateral procedural norms presupposed shared physical geography — adjacent territories, common watercourses, overlapping airsheds. The GHG–climate harm pathway requires no such proximity. The Court adopts the IPCC definition of the climate system as the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere in interaction — a physical system indifferent to national borders. Scoping a protection obligation for a global common to a bilateral spatial relationship does not produce a narrower version of the same norm; it produces a categorically incoherent one.

The Two-Level Procedural Framework

¶299 does not exhaust the procedural dimension of the Opinion. States must protect procedural rights in the climate context — public participation, access to climate information, climate education and access to justice. The IACtHR in AO-32/25 confirmed the same requirements under the American Convention with particular force, addressing participation in climate decision-making, meaningful access to climate risk information, and effective judicial remedies. Cárdenas situates these alongside notification and consultation as connected procedural innovations of the Opinion, while El Mahmoud, Jahn and Vinken frame the wider movement as a “deepened proceduralisation” of international environmental law operating at both institutional and material levels.

The relationship between these two levels is not decorative. A state that formulates fossil fuel policy without genuine domestic public engagement and then presents the international community with a fait accompli has breached both the domestic procedural right and the international consultation obligation simultaneously. International consultation cannot be authentic if domestic deliberation never took place. The IPCC dimension adds a substantive constraint: the Court treats IPCC assessment reports as the authoritative scientific benchmark for calibrating due diligence (¶284), meaning that procedural consultation which systematically disregards remaining carbon budgets and 1.5°C pathways will fail the meaningful engagement threshold of ¶299.

When Procedure Becomes Substance

¶427 holds that failure to take appropriate action — including through fossil fuel production and consumption, the granting of exploration licences, or the provision of subsidies — may constitute an internationally wrongful act.

In Pulp Mills, procedural and substantive obligations were independently answerable because both had the same bilateral scope and the same identifiable factual subject matter. The severability was coherent precisely because both obligations ran to Argentina and concerned the same shared river. Where ¶427’s wrongfulness threshold is engaged in the global climate context, that structural symmetry breaks down. A state that grants fossil fuel exploration licences in circumstances engaging ¶427, without prior multilateral consultation, is not committing a procedural failure that runs alongside a separate substantive one. Failure to engage the multilateral governance framework is direct and probative evidence that the state has not employed “all the means at its disposal” to prevent significant harm — the Court’s articulation of the due diligence test, calibrated through CBDR-RC capabilities, at ¶290. The procedural failure is partly constitutive of the substantive failure, not merely adjacent to it. Brunnée argues that the Court is “intent on overcoming” the Pulp Mills approach precisely because, in the context of harm prevention, “procedural elements… are tightly intertwined with the substantive goal of harm prevention, such that the latter could not be achieved without the former.”

The point is narrower than total collapse. Where ¶427’s threshold is not reached, ¶299 retains its independent force and the procedural-substantive severability Pulp Mills established survives. Where conduct crosses both thresholds simultaneously, that clean separation no longer holds.

The Enforcement Gap and What Comes Next

Two enforcement deficits persist. Under ARSIWA Article 48(2)(b), non-injured states invoking erga omnes responsibility may seek reparation in the interest of the beneficiaries of the breached obligation. The Court confines non-injured states to cessation and non-repetition without engaging Article 48(2)(b) at all — a limitation Tigre, Martini and Cohen identify as one of the most significant gaps in the remedial framework. For small island states facing existential harm, reparation in the interest of beneficiaries is the most practically significant remedy under settled secondary rules. Separately, the IACtHR in AO-32/25 has recognised environmental harm prevention as a jus cogens norm, activating ARSIWA Articles 40–41. The ICJ has left that question open. Alexander identifies both the erga omnes character of climate obligations and their relationship to jus cogens as among the most consequential unresolved issues, and Lange and Schophaus similarly mark the Court’s confinement of non-injured states to cessation and non-repetition as a deliberate restraint that leaves the enforcement framework incomplete.

Further, the remedial picture for states that have exited the Paris Agreement is stark. The primary mechanisms for demonstrating procedural compliance — NDC submission, transparency reporting, Global Stocktake participation — are Paris Agreement-mediated. A withdrawn state has lost its principal means of satisfying the customary obligation within the framework, and the burden of demonstrating compliance through equivalent alternative engagement rests squarely with it (¶314). How heavy that burden is turns to the Opinion’s framework for differentiation — and it is here that the Opinion’s treatment of CBDR-RC warrants scrutiny. Vice-President Sebutinde’s separate opinion for instance rightly criticises the Court for diminishing CBDR-RC by subsuming it under equity (¶¶9–12), and for failing to recognise that Annex I high-emitting states bear additional obligations to take the lead in combating climate change (¶11; see further Lupin). This criticism bears directly on the non-repetition remedy: a state whose climate decisions have material implications for whether 1.5°C remains achievable should face a more institutionally demanding non-repetition commitment than a state at the margins of global emissions.

Continuous in trigger, collective in addressee, and spatially indifferent in scope, the systemic consultation obligation ¶299 establishes represents a structural transformation of procedural environmental law. Whether enforcement evolves to match it is the question that now falls to litigants, future advisory proceedings, and the gradual accumulation of state practice.