On 23 July 2025, the International Court of Justice (ICJ) issued an advisory opinion regarding States’ legal obligations in relation to addressing climate change (hereafter referred to as “the Opinion”) at the request of the Republic of Vanuatu and 91 others. The ICJ is the highest court of the United Nations (UN) and while the Opinion is not a legally binding judgment, it carries significant influence on how international law is understood and used.
The Opinion is expected to be used in State to State litigation as well as climate litigation at the domestic level against a State. Together with the advisory opinions published by the International Tribunal for the Law of the Sea and the Inter-American Court of Human Rights[1], this Opinion sets the stage for governments and major private actors to find it increasingly difficult to permit or allow inaction in the climate and nature-related transition.
The Opinion
The Opinion clarifies that States under UNFCCC agreements including the Paris Agreement and subsequent agreements have an obligation to:
- adopt mitigation and adaptation measures;
- create and publish ambitious Nationally Determined Contributions (NDCs) with due diligence and in line with best available science to deliver a 1.5 degree world[2]; and
- implement the ambition of their NDCs in their domestic laws including enforcement mechanisms.
The Opinion also notes that the positions of States as developed or developing is not static. States can be held liable for the acts or omissions of private actors (including companies) in their jurisdiction and the failure by States to avoid foreseeable harm. For example, to regulate or constrain production of fossil fuels or to subsidise it, could constitute a breach of international law. Per the Opinion, the legal consequences for breaching obligations could include:
- stopping and/or agreeing not to repeat wrongful actions or omissions; and
- full restitution, compensation and/or damages if certain conditions are met.
The Opinion noted that States’ obligations are also present in customary international law, human rights law and environmental law and therefore obligations are not limited to UNFCCC signatory parties.
There remain areas where the Opinion is silent, such as issues of causation and attribution that the ICJ did not address. It will take time to see how this is applied in specific cases. Interestingly this is the first ICJ Opinion in its almost 80 year history in which all 15 judges unanimously concurred.
In addition to the possibility of increased litigation or threat of litigation, it is possible that there will be new efforts both to amend existing international frameworks to further implement the findings of the ICJ or to change or alter the obligations identified in the Opinion.
The intersection with transition plans
Both NDCs and private transition plans can be interrelated tools in the delivery of States commitments. Ambitious NDCs that set clear directionality and policy priorities provide certainty to business and finance in committing time and money to the transition now as the opportunities grow, rather than later when the costs of inaction exacerbate losses from extreme weather and status quo investments embed obsolesce. Reasonable transition plan disclosure requirements could be a component of a States’ domestic law response in line with the Opinion’s position. Transition plans from businesses and finance, based on materiality assessments and consistent with existing disclosure standards, can benefit those that undertake them as a key strategy building exercise for future proofing. Published transition plans can also enhance transparency and assist States in understanding how business and finance can accelerate the transition and for prioritising areas for policy support.
In the best possible world, the Opinion will be seen as an opportunity for States to analyse the cost and benefits of government time and resources. It is possible that States may focus on generating support for amendments to lower the bar on what is required of States under the existing obligations considered by the ICJ, which could lead to more negotiation of legal documentation. A second – but not mutually exclusive – option is spending time and resources on upgrading regulatory frameworks and rules to accelerate the tripling of renewables, doubling energy efficiency and reaping the benefits of natural capital and biodiversity gains to enable resilient energy security with increased jobs and increased opportunities for business.
[1] Advisory opinions were published in May 2024 by the International Tribunal for the Law of the Sea (addressing the duty of States to prevent environmental harm and protect the marine environment) and in July 2025 by the Inter-American Court of Human Rights (recognising the right to a healthy environment as a fundamental human right and highlighting extraterritorial responsibility of States for environmental harm that affects human rights in other countries). As at October 2025, an advisory opinion request is pending at the African Court of Human and Peoples’ Rights (seeking to clarify human rights obligations of African States concerning climate change mitigation and adaptation, particularly in the context of the disproportionate impact of climate change).
[2] Best available science is the IPCC reports, as agreed by the parties to the Advisory Opinion.