ICJ Advisory Opinion on Climate Change: determining States obligations beyond the UNFCCC[1]

23/01/2025

As climate litigation becomes increasingly more frequent, the case that has the potential to influence and inform all future cases has just begun its final stages of deliberation. The International Court of Justice (ICJ) is deliberating over 2 questions referred by the UN General Assembly (UNGA) (in Res 77/276) concerning obligations of States under international law with regards to climate change. Although non-binding, the advisory opinion will hold significant legal weight and moral authority (given the ICJ’s status) both in relation to future litigation, as well as in terms of potentially influencing States to uphold their climate commitments.

UNGA’s referred questions

The UNGA Resolution asked the ICJ to consider two questions. Firstly, what obligations States have under international law to protect the climate system, and other parts of the environment, from anthropogenic emissions of greenhouse gases for present and future generations. Secondly, what are the legal consequences of acts or omissions that breach these obligations and cause significant harm to the climate system. This second question is explicitly posed with respect to (i) States who are particularly affected or vulnerable, due to their circumstances, to adverse effects of climate change; and (ii) present and future generations. This blog post focuses primarily on the first question, given that the arguments raised by Countries on the second question are largely determined by what they see as a source of obligation when responding to the first question.

Timeline of case

The UNGA requested the advisory opinion by consensus on 29th March 2023, spearheaded by Vanuatu and other Small Island Developing States (SIDs). By the deadline of 22nd March 2024, a record-breaking 91 States and authorised organisations had filed written statements to be considered before the Court. A further 62 written comments were filed by 16th August. Oral hearings then took place between 2nd-13th December with 96 States and 11 international organisations participating. Following the conclusion of these hearings, the Court then began its deliberation.  

On 13th December, following the final oral hearing, four of the presiding ICJ judges posed questions open to all participants with a deadline of 20th December for responses.

  • Judge Cleveland asked what the participants see as the specific obligations, if any, of fossil fuel producing States.
  • Judge Tladi asked whether the ‘object and purpose’ of the Paris Agreement, and general climate change treaty framework, has any effect on the interpretation that, to the extent that Article 4 of the Agreement contains obligations related to NDCs, these are procedural in nature, a conclusion reached by many participants.
  • Judge Aurescu asked for development on the legal content, and link with relevant human rights, of a ‘right to a clean, healthy and sustainable environment’ (‘RHSE’) that some participants have argued for.
  • Judge Charlseworth asked participants’ opinions on the significance of the declarations made by some States on becoming parties to the UNFCCC and the Paris Agreement to the effect that no provision in these agreements may be interpreted as derogating from principles of general international law or any claims or rights concerning compensation or liability due to the adverse effects of climate change.

Central legal arguments

The two questions referred to the Court by UNGA focus on (1) obligations and (2) remedial consequences of a breach, respectively. Thus, the legal arguments centre around the sources of these obligations and what mechanisms may be used as remedies; those most responsible for climate change generally arguing for a narrow approach to both these points, with the most vulnerable taking the opposite approach. This divide runs through discussions of four (non-comprehensive) central legal arguments over the relevance of: (a) the climate change treaties; (b) the no-harm principle; (c) international human rights; and (d) the rules of State Responsibility. In general, industrialised and developed States seek to restrict the source of State obligations to the core climate treaties and exclude the application of (b), (c) and (d) as much as possible, whilst more vulnerable States generally welcome a more expansive and holistic interpretation and use of customary international law by the Court.

(a) Status of the climate change treaties

Potentially the first issue the Court must answer is what sources of international law apply, responding to those who argue that the core climate treaties (the UNFCCC, the Paris Agreement and the Kyoto Protocol) are the sole sources of obligations in this context (the narrow approach described above, sustained by those more responsible). Such a finding would lead to much greater discretion for States given that most obligations under these treaties lack enforcement mechanisms and they are mostly of a procedural nature, particularly those in the Paris Agreement. Two frequent arguments are that: (i) the treaties are lex specialis and so exclude the operation of customary international law; and/or (ii) to go outside of them would undermine the value of international cooperation embedded within them. These arguments speak of the sources of international law and the relationship between them. (ii) is unlikely to be successful due to its wide implications. If it was backed by principle, it could mean the exclusion of supplementing judgements with customary international law in all subject matters involving treaties since they arguably all represent cooperation. This argument serves, and is predominantly supported by, many developed States who want the ICJ to carry that over into their advisory opinion.

Focusing on (i), lex specialis would mean the more specific set of rules, that being the treaties, takes precedence and other rules do not apply. However, its application in this case is supported by a minority and opposed by many. The opposing view is that other, more stringent, obligations from sources other than the treaties are also applicable. Following the different submissions put before the Court, it appears as if the ICJ’s task is one of determining the correct interpretation of the lex specialis principle. Those against its application, like Samoa, cite ILC Commentaries to Art 55 ARSIWA[2] which states that the principle applies only when there is (1) a conflict of norms; or (2) a discernible exclusionary intention. They then argue that neither is present. For (2), several states made declarations on ratification of the Paris Agreement (and others) that their acceptance was on the basis that the applicability of other international law was not negated. This latter point was the focus of Judge Charlesworth’s question, implying that the Court sees it as potentially relevant. For (1), there are no binding obligations in conflict. ITLOS reached this conclusion, finding the UNFCCC not to be lex specialis in the context of UNCLOS[3]. Importantly, those of the opposing view, such as Saudi Arabia, do not give evidence of any relevant conflict either since they rely on a formulation which omits the need for (1) or (2)[4]: they suggest that the mere fact that norms cover the same subject matter is enough. Furthermore, Saudi Arabia, in response to Judge Charlesworth, only comment on the inability of the declarations to alter interpretation of the treaty, given the small number of them and the lack of acceptance by other Parties. However, they make no reference as to the significance of them in relation to the lex specialis status of the core treaties.

Thus, the determination likely hinges on which formulation is accepted, although Saudi Arabia’s source does reference the purpose of lex specialis being to obtain a single set of ‘compatible obligations’, thus potentially requiring an initial conflict of obligations. Whichever way it is decided, the Court’s conclusion on this matter will have a significant impact on their answer to both referred questions since the treaties also have their own remedial mechanisms, whereas others advocate for the rules of State Responsibility (as will be discussed below).

(b) No-harm principle

On the assumption that customary international law applies, the Court must then decide what obligations can be drawn from it, such as the no-harm principle; an obligation of due diligence and prevention to ensure that activities within the jurisdiction or control of one State do not result in significant transboundary harm to another State’s territory or areas beyond national jurisdiction. Those who support the lex specialis approach also argue that, even if customary international law was not excluded, the no-harm principle is inapplicable because (i) it differs from traditional pollution cases due to a lack of causal link; and (ii) the standard of due diligence is unclear. (i) relies on the idea that GHG emissions have multiple and complex sources as well as indirect impacts on many states, it is not the same as one State causing direct harm to another with a single source of pollution (such as a smelter factory). Those who oppose this position suggest that it is essentially disapplying the law due to it being too difficult to apply, despite the ICJ’s history of dealing with difficult causality questions. Furthermore, ITLOS found GHG emissions to meet UNCLOS’ specific definition of pollution; the ICJ may explore whether this can be extrapolated, ignoring any distinction. Establishing causality, they argue, would be possible given the advancements in attribution science allowing us to forensically determine which emissions have a causative link to which harms and to what degree. Some States disagree, counter-arguing that the science still is not sophisticated enough. As for (ii), Samoa suggests that the standard of due diligence could be informed by the long-term goals of the Paris Agreement as well as other circumstances of each case. The UK, for its part, argued that the standard of due diligence is included in the climate change treaties.

Samoa also suggests, in response to Judge Cleveland’s question, that the no-harm principle, as well as international human rights (c), should apply to fossil fuel producers. However, those that oppose this view suggest that the obligations of fossil fuel producers fall completely outside the scope of the questions referred and thus outside the Court’s jurisdiction.

(c) International human rights

One source of obligations that the ICJ has already shown a notable emphasis on is the application of international human rights. Most States accept that climate change does, or potentially could, adversely affect the enjoyment of human rights for individuals, rights such as: the right to life, the right to an adequate standard of living, cultural rights and more. Those that assert the existence of the RHSE as a standalone universal human right responded to Judge Aurescu by arguing its content is both substantive (e.g. requiring clean air, safe and liveable climate, sustainable food production) and procedural (e.g. right to access environmental information). Furthermore, they argue it links to other human rights (like those mentioned above) given that it is a necessary pre-condition to the enjoyment of them. The dispute for the Court to determine is whether such rights are able to create obligations on States in this context. Some developed States argue that human rights instruments are not sufficiently universal and do not define obligations amongst States for harm occurring outside a State’s territory or jurisdiction and so, as New Zealand argues, cannot apply to climate change as it is extra-territorial harm.

(d) State Responsibility

Those who want more stringent remedial consequences for breach of climate change obligations advocate the application of rules on state responsibility for internationally wrongful acts. The ILC Articles on State Responsibility, which are not binding but are recognised as generally codifying customary international law, state that ‘[e]very internationally wrongful act of a State entails the international responsibility of that State’[5]. States will be legally responsible for an international wrong only if there is a breach of an international obligation by a State by act or omission which is attributable to it[6]. Qualifying breaches would have to be remedied by upholding the relevant obligation, ceasing the wrongful act, and giving full reparation for any injury caused. By contrast, some argue these rules are inappropriate in this context and remedial mechanisms in the climate change treaties are more applicable, mostly using the same causal arguments related to not applying the no-harm principle. The Court’s determination on this matter will be significant due to the many vulnerable States pointing to the inadequacies in current climate financing -especially climate finance based on the Convention and the Paris Agreement- and its propensity to increase the debt burden on their vulnerable climate-sensitive economies. This concern was strongly voiced by Kenya, for example, who during the hearings, suggested that unilateral debt restricting and cancellation ought to be considered as potentially appropriate satisfaction with regards to the legal consequences of the question referred[7]. Latin American and Caribbean states also asked the Court to consider debt relief as satisfaction.

Legal Consequences

The second question concerned the legal consequences for States that caused significant harm to the climate system and other parts of the environment with respect to states (particularly small island developing States) and peoples and individuals of present and future generations. On this point, States framed their answers according to their interpretation of the applicable law. I.e., if they argued the law of state responsibility applies, the legal consequences would include cessation and reparation (in the form of compensation for loss and damages, as some states argued). Other interventions focused on their obligation within borders: regulatory obligations in a time of climate emergency. Broadly speaking, developed states tend to favour an interpretation that restricts the source of obligations to the core climate treaties because the remedial mechanisms under those treaties are more limited than remedies under the other identified sources of obligation examined above. 

Significance of oral hearings

As well as reaffirming parts of States’ written statements and comments, the oral hearings afforded the more vulnerable States an opportunity to communicate their lived experience of damaging effects of climate change. Through the use of personal testimony and photos and videos of cultural artefacts, legal arguments of adversely affected States were strengthened by humanising the existential threat of climate change. On a subject as wide-reaching and scientific as climate change, grounding the discussion in the real-world impact gives the Court much needed context.

Wider implication: Another avenue for vulnerable States

Within the complex issues involved in this case, it must be remembered that climate change involves inherent inequality, which is somewhat recognised by the core principle of the climate regime: common but differentiated responsibilities. Developed States tend to be those who have contributed most to emissions and have the resources to adapt to the adverse effects of climate change whereas smaller, developing states bear the least responsibility but are the most affected and vulnerable. This inequality permeates the UN climate negotiations: delegations vary significantly in resources, size and expertise and most developing countries don’t have legal experts in their teams and come with small delegations.

The appeal to the ICJ is a chance for vulnerable states to pursue an alternative to climate negotiations. The unfairness of the negotiations and their limited success, especially for vulnerable countries’ needs, have driven the search for the alternative avenue of climate litigation, with the ICJ’s advisory opinion being a critical piece of the puzzle. This advisory opinion could significantly impact future negotiations and implementation of climate instruments by providing an authoritative statement that all States could not afford to ignore.  With no further submissions to the Court expected, the next update to the case will be the issuing of the advisory opinion. This will be delivered at a date not yet announced but which will likely be in 2025.


[1] With thanks to Dylan Gannaway for preparing this post.

[2] ILC Commentaries to Art 55, point 4 (2001)

[3] ITLOS, Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law (Request for Advisory Opinion submitted to the Tribunal), Advisory Opinion, Case No. 31, 21 May 2024, para. 224

[4] ILC’s Study Group Fragmentation Report, para 2.5 (2006)

[5] Articles on the Responsibility of States for Internationally Wrongful Acts (ARSIWA), Article 1

[6] ARSIWA, Article 2

[7] Kenya’s oral hearing, Friday 6th December, para 35