The ICJ Advisory Opinion on Climate Change: What It Means for the Convention on Biological Diversity

This week’s General Assembly’s resolution welcoming the International Court of Justice’s Advisory Opinion on Obligations of States in Respect of Climate Change provides significant guidance. It calls upon all States to ‘comply with their respective obligations under international law to ensure the protection of the climate system and other parts of the environment from anthropogenic greenhouse gas emissions’. The resolution was supported by 141 votes in favour; eight states voted against, and there were 28 abstentions.

As noted by the unanimous bench at the ICJ, the biosphere is part of the ‘climate system’. Legal obligations to protect the climate system flow not just from the climate treaties, but from customary international law and other treaties, including the Convention on Biological Diversity (CBD).The upcoming Conference of the Parties to the Convention on Biological Diversity (COP 17) will mark the first global review of collective progress towards the implementation of the Kunming-Montreal Global Biodiversity Framework (GBF). The GBF responds to the alarming recognition by scientists that the biosphere ‘is being altered to an unparalleled degree across all spatial scales’ (IPBES). 

Although formally non-binding, the Advisory Opinion represents an authoritative interpretation of the obligations of states in respect of climate change. The General Assembly notes the Court’s finding that a breach by a State of any of its obligations constitutes an internationally wrongful act, with legal consequences including duties of reparation. For the CBD Secretariat, which serves the parties to the CBD (CBD Article 24), it is important that parties are informed of the opinion and equipped to consider its implications. Parties cannot reasonably be expected to give effect to the Advisory Opinion’s reasoning in their National Biodiversity Strategies and Action Plans (NBSAPs) and GBF reporting if the opinion and its consequences are not actively communicated, analysed, and made accessible.  International organizations and other actors play an important role in sharing information across a fragmented legal system.

Applicable Law and Relevant Conduct

The General Assembly’s original request invited the Court to have ‘particular regard to’ the UN Charter, the human rights covenants, the UNFCCC and Paris Agreement, the UN Convention on the Law of the Sea, the duty of due diligence,  prevention, and protection of the marine environment. As noted by the General Assembly resolution welcoming the Advisory Opinion, the Court found that the applicable law also includes the CBD and other environment treaties (Advisory Opinion, ¶172).  The Court rejected any ‘lex specialis’ argument that the Paris Agreement displaces other treaties or custom. Crucially, the Court was unanimous in its opinion stated in the dispositif that, inter alia, states parties to the CBD have obligations to ensure the protection of the climate system and other parts of the environment from anthropogenic greenhouse gas emissions (Advisory Opinion, ¶457(3)(C)). A breach of these obligations, alongside the prominent obligations flowing from the Paris Agreement and other sources, constitutes an internationally wrongful act entailing responsibility (Advisory Opinion, ¶457(4)).

The Court’s definition of relevant conduct is important for CBD parties. Conduct is not limited to direct emissions from burning oil, coal or gas: it comprises all actions or omissions of states which result in the climate system being adversely affected by anthropogenic GHG emissions (Advisory Opinion, ¶94). The Court noted that the weakening or destruction of carbon reservoirs and sinks increases the concentration of GHGs in the atmosphere (Advisory Opinion, ¶72; See also Declaration of Judge Cleveland). The implication for the CBD is that degrading forests, draining wetlands, destroying mangroves, or failing to protect marine carbon sinks are all conduct that may breach obligations to protect the climate system. 

CBD Obligations Specifically Identified by the Court

In its consideration of the substantive obligations imposed by the CBD, as invited by some participants including the IUCN, the Court identified Article 3 – ensuring that activities within a state’s jurisdiction or control do not cause damage to the environment of other states or to areas beyond national jurisdiction – as reflective of the customary duty to prevent significant harm (Advisory Opinion ¶327). Article 6 (national strategies, plans, and programs) was noted as encompassing measures for mitigation of and/or adaptation to climate change. Article 7 was cited for its requirement to identify and monitor processes with significant adverse impacts on biodiversity. Most consequentially, the Court read Article 8(l) – the obligation to regulate or manage relevant processes and categories of activities – as expressly extending to those which contribute to GHGs (Advisory Opinion, ¶329). The Court also pointed to GBF Target 8 on minimising climate impacts on biodiversity. Crucially, states must take their CBD obligations into account when implementing their obligations under the climate change treaties and customary international law (Advisory Opinion, ¶335); for example, by ensuring that wind turbines prevent harm to bats and birds, or carbon sequestration maintains old growth or biodiverse forests. 

In elaborating on the duty to prevent significant harm, the Court adopted the conclusion by the International Tribunal for the Law of the Sea (ITLOS) in its 2024 advisory opinion that the standard of due diligence in protecting the environment is ‘stringent’. Due diligence ‘entails not only the adoption of appropriate rules and measures, but also a certain level of vigilance in their enforcement and the exercise of administrative control’ (Advisory Opinion, ¶ 138). This matters for the CBD because most of its obligations are obligations of conduct, often qualified by phrases like ‘as far as possible and as appropriate’. The Court’s reasoning suggests these qualifiers have limits: states must adopt rules, enforce them, and supervise compliance, with the standard tightening as the science and risks become clearer.

Due Diligence Reaches Private Actors

The Court’s comments about private conduct are also significant for CBD parties, especially where most biodiversity loss is driven by private actors: agribusiness, fisheries, forestry, and infrastructure developers. The Court restated ITLOS’s observations that the ‘obligation of due diligence is particularly relevant in a situation in which the activities in question are mostly carried out by private persons or entities’ (Advisory Opinion, ¶252). Domestic climate mitigation measures can also be ecosystem protection measures, encompassing regulation of private activities that significantly contribute to higher GHG concentrations. Moreover, the cumulative effect of acts undertaken by various states and by private actors subject to their respective jurisdiction or control is recognised by the Court (Advisory Opinion, ¶276). The recognition that diffuse and multifaceted forms of conduct attracts the duty to prevent significant harm to the climate system (Advisory Opinion, ¶ 279) addresses the problem recognized by environmental lawyers such as Nelson, as ‘death by a thousand cuts’. With the Court’s recognition that appropriate measures to avoid harm include legislation, administrative procedures and an enforcement mechanism necessary to regulate the activities in question (Advisory Opinion, ¶281), the duty upon states to regulate private actors driving biodiversity loss is arguably now legally actionable.

Practical implications for companies that are dependent on ecosystem services, or which have significant impacts on nature, are manifold. Biodiversity threats, traditionally addressed as a matter for reputational management and corporate social responsibility (CSR), are now recognized as affecting nature-related risks and directors’ duties (eg, in Australia, Canada and the Philippines). The Advisory Opinion extends law’s reach. Once states are expected to regulate private activity to meet stringent standards of due diligence, and cumulative private conduct is recognised as contributing to significant harm, the legal and financial exposure of companies whose operations drive biodiversity loss is clearer. Audit committees will need to consider biodiversity-related provisions; insurers and lenders are likely to extend climate-style scrutiny to biodiversity. The standard of care of directors is heightened not only for fossil fuel and emissions-intensive companies (as Higgins, Bush and Robinson have shown), but for companies in agribusiness, fisheries, forestry, extractives, infrastructure, pharmaceuticals, and finance. The anticipation of liability may be how the Advisory Opinion affects real-world behavioural change well before any litigation reaches a court.

COP Decisions as ‘Subsequent Agreements’ 

Relying on Article 31(3)(a) VCLT, the Court held that decisions of COPs may constitute subsequent agreements insofar as they express agreement in substance between the parties regarding the interpretation of the treaty (Advisory Opinion, ¶184). The Court found that the Glasgow Climate Pact and the first Global Stocktake constituted such an agreement with respect to the Paris Agreement’s temperature goal. (Advisory Opinion, ¶ 224). CBD COP decisions may have similar legal significance. The GBF is the obvious candidate: adopted by consensus among 196 parties, with specific numerical targets and deadlines. Target 3 (30×30 conservation), Target 8 (minimising climate impacts on biodiversity), Target 18 (eliminating or reforming USD 500 billion in harmful subsidies), and Target 19 (mobilising USD 200 billion per year, including USD 30 billion for developing countries) are all candidates for treatment as subsequent agreements that fix the content of vague CBD obligations under Articles 6, 7, 8, 11, and 20. 

Legal Consequences

The Court unanimously held that breach of the obligations it identified constitutes an internationally wrongful act entailing the responsibility of the breaching state. Legal consequences include cessation, assurances and guarantees of non-repetition and full reparation to injured states in the form of restitution, compensation, and satisfaction – provided the general conditions of state responsibility are met, including a sufficiently direct and certain causal nexus. 

Most striking for the CBD is the Court’s view that the remedy of restitution ‘may take the form of reconstructing damaged or destroyed infrastructure, and restoring ecosystems and biodiversity’ (Advisory Opinion, ¶451). While the Court did not opine on the level of restitution required, ecological restoration – which had also been expressly endorsed by the ITLOS Advisory Opinion – is now clearly recognised as relevant to remedies. In a context of growing biodiversity litigation at the domestic, regional and international level (as tracked by Futhazar, Maljean-Dubois and Razzaque), such a determination in concreto can reasonably be contemplated. 

Conclusion

The ICJ’s systemic approach to obligations from the climate treaties and other areas of international law has been restated by the General Assembly, which has recorded its determination to translate the Court’s findings into enhanced multilateral cooperation. This integration of the broad foundation of climate obligations has attracted much commentary and discussion, including through data visualisations connecting applicable treaties, while the CBD’s relevance to climate has long been analysed in legal scholarship (including by van Asselt, McCormack and Caddell). This blogpiece has shown that the Court has endorsed the CBD’s enduring role in the protection of the climate system, and its COP decisions – above all the GBF – are given potential interpretive weight. For CBD parties and non-state actors, the Convention is an important source of legal obligations that are increasingly enforceable. The Secretariat has a responsibility to disseminate the effects of the Advisory Opinion on the CBD and the obligations of its parties. 

The views expressed herein are those of the author and do not necessarily reflect the views of the United Nations.

The image attached to this post is attributed to McCoy,  Frederick, et al. Natural History of Victoria : Prodromus of the Zoology of Victoria. By authority: J. Ferres, government printer, 1885, https://www.biodiversitylibrary.org/page/41695986.