Closing the Silences

The International Court of Justice’s (ICJ’s) Advisory Opinion on Climate Change arrived with force. Given its far-reaching implications, there is no doubt that the opinion now will be subject to conflicting interpretations. In this post, I highlight the interpretive compass that the opinion supplies to those who will now interpret what the ICJ is saying and not saying. 

At a substantive level, the ICJ clarified a number of important climate obligations (see analysis by e.g. Wewerinke-Singh and Reetz), characterizing them as obligations erga omnes (paras 439-443), upgrading 1.5°C from aspiration to an agreed temperature goal (paras 224-225), demanding a stringent due-diligence test (para 246) and establishing that unlawful warming can entail full reparation (paras 420 and 449-250, see analysis by e.g. Tigre, Martini, Cohen and Rocha). But at this level, a number of questions remain, as for example noted by von Bernstorff and Venzke and Odermatt. New fossil licenses or subsidies may be wrongful (para 427), but when are they wrongful? Is there now a human right to a clean, healthy and sustainable environment; what did the ICJ mean when saying that this right is “inherent in the enjoyment of other human rights” (para 393, see analysis by e.g. Boyd)?  And what does “full reparation” more concretely mean in a climate context?

However, the ICJ’s opinion did more than list climate obligations; at a second, methodological level, it showed how those obligations should be read – weaving treaty text, General Assembly resolutions and foundational principles into a single, coherent rule-set (as also analysed by Wewerinke-Singh). 

And since that same interpretive compass as the ICJ itself applied should now, arguably, guide readers of the opinion itself, many of the uncertainties and gaps critics spotlight can arguably be closed by applying exactly the method the ICJ just deployed.

One Text, Different Interpretive Lenses

To understand the ICJ’s method of interpretation, it is useful to begin with how some of the involved States argued in the written proceedings, either to indirectly avoid or to allocate responsibility. Ronald Dworkin famously said, in his book Law’s Empire, that any legal interpretation must meet the double test of fit and justification. In this context, fit means straightforward textual support—does the reading actually map onto the legal materials under scrutiny? Justification means the principled rationale for preferring one permissible reading over another: the reading must show the law as a coherent scheme of principles (e.g., equal concern and respect, fairness, non-arbitrariness, protection of rights, and integrity) rather than as a patchwork of ad hoc decisions.

Used as a heuristic rather than a rigid dichotomy, this distinction helps to read, for example, the written statements of the United States, the European Union (EU), and Vanuatu. They, arguably, line up along a spectrum of justification: at one end, consent-first positions justify their readings by pointing to explicit acceptance and minimal extension beyond the text; at the other, coherence-first positions justify them by showing how rules and principles hang together as a consistent whole that treats like cases alike and expresses the community’s rights-based commitments. Differences in which materials are brought into view—and how they are read—thus reflect, even if not always made explicit, how each party justifies its interpretation in terms of principle.

The United States adopted the consent-first view. Climate law, it argued, is basically comprised of the Paris Agreement, “the clearest expression of States’ consent.” Obligations are procedural. There is no free-standing due diligence or human rights duty, and any putative custom is satisfied once a State follows the Paris Agreement. 

Vanuatu was at the opposite end of the spectrum, adopting the coherence-first view. Invoking no-harm, equity, and precaution alongside the treaty text, it asked the ICJ to craft a single, normatively coherent rule-set, concluding, for example, that fossil-fuel subsidies cannot be squared with existing obligations.

Everyone else sat at or between those poles. The decisive variable was how far each brief let principles and other duties reshape the interpretation of rules. Saudi Arabia and China stayed close to the U.S. line but selectively invoked the principle of Common But Differentiated Responsibilities and Respective Capabilities (CBDR-RC) and sustainable development while avoiding no-harm. The EU leaned toward Vanuatu, yet softened CBDR-RC and stressed party consent when it came to remedies, hoping to keep classic “full reparation” rules at bay. The other statements can be read along the same lines.

Across the spectrum, all sides could thus claim textual “fit”; what changed was, basically, the weight granted to e.g., no-harm, equity, and CBDR-RC, i.e. how their textual readings were justified in the legal framework. Even when not stated outright, this difference in weighting operated — using the substantive/methodological distinction — on the methodological level: it can be reconstructed as divergent readings of the interpretation rules in articles 31–33 in the Vienna Convention on the Law of Treaties (VCLT) and corresponding customary rules of interpretation. Depending on the justificatory starting point  – consent-first or coherence-first – different VCLT components take centre stage (e.g., ordinary meaning versus context and object-and-purpose, the force of subsequent agreement/practice, and which relevant rules are pulled into the frame).

The ICJ’s prescribed method of interpretation

Viewed through the “fit and justification” test, the ICJ clearly followed Vanuatu’s path: it chose a reading that weaves together the treaties, customary law, human rights, and general principles into a textual and normatively coherent web of rules (see also the excellent analysis by Wewerinke-Singh).  

Early in the advisory opinion, the judges set out the familiar doctrinal gateway for the treaty-based parts of their analysis: interpretation begins with Articles 31-33 of VCLT. For obligations arising under custom and general principles, the ICJ applies a parallel method – grounding rules in their accepted formulation, reading them in context, and integrating “other relevant rules” where applicable. What follows, in both strands, is anything but a narrow consent-only exercise. Some examples are provided below.

Treaty text interpreted within a principled frame

The ICJ identifies the 1.5°C floor from hard sources – the Glasgow and Dubai CMA decisions (Conference of the Parties serving as the meeting of the Parties to the Paris Agreement) treated as a “subsequent agreement” under VCLT 31(3)(a), read together with the “best available science” clause of Paris Art. 4(1) (paras224-225). This reading takes place within the interpretive frame set earlier (paras 146–161), in which the no-harm duty and the principles of precaution, cooperation, and equity/CBDR-RC inform an object-and-purpose analysis. The result is that 1.5°C, rather than “well below 2°C”, is treated as the benchmark for all States’ conduct.

Due diligence with sharper edges

Drawing on the customary no-harm rule (para 135), the ICJ said the due-diligence obligation under the Paris Agreement means a Nationally Determined Contribution (NDC) is lawful only if it can credibly keep the State on a 1.5°C-consistent path (paras 228, 251). “Highest possible ambition” thus requires not just progressive targets on paper but concrete implementation because letting emissions run beyond that path would violate the no-harm duty.

Soft-law carried into the core

General Assembly Resolution 76/300 is treated by the ICJ as evidencing broad opinio juris (paras 392-393) of a right to a clean, healthy and sustainable environment. In the ICJ’s view, when read together with existing rights treaties, the resolution reinforces the view that climate action must protect human dignity and health, supplying one of several normative pillars, contrary to the United States. submission that branded the resolution as merely aspirational.

Reparation sized for climate damage

The ICJ confirmed that the Paris regime is not a lex specialis that displaces the general law of State responsibility, so the (In many aspects) customary rules of “full reparation” expressed by the  International Law Commission (ILC) remains fully in force (paras 450-453). The ICJ justified that move by implying (paras 418-420) that only the ILC framework can uphold the “object and purpose” of the climate treaties – protecting people and ecosystems from dangerous harm – when losses are large-scale and irreversible. Hence, “full reparation” may include ecosystem restoration, rebuilt defences, and compensation for affected individuals, going beyond the Paris finance channels the ICJ discussed earlier. (As a side note, a justification of this interpretation, fully consistent with the ICJ’s approach, would have been to point out the obvious inconsistency that otherwise would have ruled: States not a party to Paris would face the full remedies regime in international law while Paris parties would “get away” with much lower liability.)

In short, for treaty interpretation, the ICJ read articles 31-33VCLT in a way that implied a tight integration of ordinary meaning, context, and “other relevant rules” with foundational duties and principles. For obligations arising under customary law or general principles, it applies a parallel, integrative method to produce a coherent and principled rule-set. 

Filling the gaps with the ICJ’s interpretation method

Run the opinion through the interpretation method the ICJ itself employed and many of its gaps arguably tighten into working rules.

Fossil licences, subsidies, and the implied phase-out

Paragraph 427 warns that continuing fossil extraction, issuing new permits, or prolonging subsidies for fossil fuel development may be an internationally wrongful act. Read alongside the CMA consensus that 1.5°C is now the legal floor, the Glasgow Climate Pact’s call to “phase-down” unabated coal and “phase-out” inefficient fossil-fuel subsidies, plus the no-harm duty and precautionary principle together with stringent due diligence, that tentative “may” arguably hardens into a presumption: unless a government can prove – with credible science and carbon-budget math – that extra fossil capacity is consistent with a 1.5°C pathway, there are now strong arguments that the project fails due diligence. In effect, the burden of proof shifts, turning “phase-out” (a term missing in the opinion) from soft pledge into the default legal presumption. Of course, a number of complex questions remain, also within the ICJ’s interpretive framework – not least how to find the right balance between the no-harm duty, pointing toward restricting fossil licenses, and the CBDR-RC principle (noting that duties prevail over principles). 

Reparation

When the ICJ addressed remedies, it quoted the ILC formula of “full reparation” but immediately explained that climate damage is often permanent and widespread. That insight pulls the concept far beyond diplomatic apologies: making victims whole can now mean restoring mangroves, rebuilding flood defences, transferring clean-tech know-how, or paying households for lost livelihoods – whatever the science and rights evidence show is actually required. The Paris finance channels are only a starting point; a State that offers less must justify why that smaller package truly repairs the harm.

Human-rights dimension

Paragraph 393 of the ICJ opinion calls a clean, healthy and sustainable environment “inherent” in existing human-rights treaties, and General Assembly Resolution 76/300 confirms broad acceptance of that view. The effect is far-reaching: whenever a policy foreseeably degrades air, water, or climate, it now engages obligations under the International Covenant on Civil and Political Rights and International Covenant on Economic, Social and Cultural Rights – unless the State can explain, in rights terms, why the interference is nevertheless permissible.

Seen in that light, the opinion’s silences are elastic restraints. Stretch them with unsupported emissions, under-funded remedies, or open-ended licensing, and they snap back as concrete legal faults. Applying the ICJ’s own method of interpretation, it will not be enough, when courts, policy makers, COP negotiators and others interpret the Opinion – taken on its own or within the wider corpus – to focus on textual fit, i.e. what the ICJ explicitly says or does not say. Any reading must harmonize with the duties and principles that permeate and justify both treaty and customary law, with particular weight on the no-harm rule, precaution, and equity/CBDR-RC. 

Closing Note

How the opinion is read in practice is, of course, another matter. Courts, arbitrators, and political actors may reject the gap-filling exercises suggested here. The near-future will show the distance between what the ICJ’s method should support and what future decision-makers will actually accept. 

At COP 30 (Conference of the Parties) in Belém, ministers will wrangle over how “sufficient” the new climate-finance goal must be, and whether “phase-down” of coal is a slogan or a legal trigger. In Brussels, the 2040 climate target faces the same test, while in Geneva, the WTO’s fossil-subsidy reform stalls over which tax breaks to cut. Read through a strict consent-only lens, and these are political choices. Read through the ICJ’s frame – science, equity, no-harm, precaution – they become legal ones: finance must be capable of delivering 1.5°C and repairing loss and damage, coal and subsidy policies must be plausibly 1.5°C-compatible, and the burden falls on governments to prove it. 

The next round of climate politics could therefore become an exercise in forensic interpretation, not in treaty drafting.