Joyeeta Gupta
On 23rd July 2025, the International Court of Justice issued its unanimous advisory opinion on climate change, to the case referred to it by the UN General Assembly. However, individual judges went beyond the consensus to also make specific points.
This simplified summary highlights the key unanimous decisions:
- Since the case concerns legal questions, the ICJ has jurisdiction to answer it. However, international law cannot alone solve the problem – other disciplines and knowledge is necessary.
- The applicable laws on climate change include not just the climate change treaties and COP decisions, but also the UN Charter, the agreements on biodiversity, ozone depletion, desertification, oceans, as well as the human rights agreements, state responsibility and general principles of international law. This is because there is no discernible intention in the climate treaties to exclude or repudiate these other laws. This implies that all parties in these different legal bodies must also further climate action, but also that the Climate Agreement can be interpreted in the light of these other agreements.
- All states have a common concern to protect the climate system and the duty of not causing significant harm to the system is a duty erga omnes (towards all). The judgement states: “Consequently, States’ obligations pertaining to the protection of the climate system and other parts of the environment from anthropogenic GHG emissions, in particular the obligation to prevent significant transboundary harm under customary international law, are obligations erga omnes.” This repairs a significant omission in the list of principles of the Climate Change Convention. It also states that such duty is accompanied by stringent due diligence [high level of care in making informed decision] and is “in accordance with their common but differentiated responsibilities and respective capabilities”.
- With respect to the climate regime, there is enough evidence that states have agreed that 1.5℃ is the agreed temperature goal of the Parties, based on the COP decision which updates the Paris Agreement, and is in line with an IPCC report that stated that 2℃ has more risks than 1.5℃ which has more risks than 1℃.
- All successive Nationally Determined Commitments (NDCs) submitted by nations under the Paris Agreement must show (a) a progressive development of obligations. Together, (b) these NDCs should be “capable of achieving the temperature goal of limiting global warming to 1.5°C above pre-industrial levels; consistent with what it needs to do to achieve the 1.5℃ target”. This counters the current trend which shows that countries collectively are moving towards a 2.7℃ world.
- With respect to phasing out fossil fuel, the Court states: “Failure of a State to take appropriate action to protect the climate system from GHG emissions — including through fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licences or the provision of fossil fuel subsidies — may constitute an internationally wrongful act which is attributable to that State. The Court also emphasizes that the internationally wrongful act in question is not the emission of GHGs per se, but the breach of conventional and customary obligations identified under question (a) pertaining to the protection of the climate system from significant harm resulting from anthropogenic emissions of such gases.” This is a very explicit statement that if phasing out fossil fuel is required to protect the climate system at 1.5℃, then not doing so is an international wrongful act. Remedies include cessation of wrongful act, reparation and compensation.
- The state is also obliged to regulate the acts of private actors as a matter of due diligence. This aims to counter regulatory capture by powerful private actors.
While, the advisory opinion is explicit on state responsibility, the adoption of 1.5℃ as the main consensus temperature target, and the kind of remedies available, it did overlook a few issues, which the declarations and statements of individual judges clarify. For example, the Right to Development is not really addressed, although both the Principles under the Climate Change Convention were mentioned as well as Human Rights instruments. Moreover, there was little reference to trade and investment law, although one of the judges emphasizes the challenges of investment law for climate action (e.g. regulatory chill). Some judges wanted a more detailed exploration of what ‘stringent due diligence’ means in terms of fossil fuel. They state: “Thus, the stringent due diligence obligations to implement such NDCs and to prevent significant transboundary harm require States to adopt and enforce regulations consistent with reducing global dependence on fossil fuels, including by phasing out production and use of fossil fuels and subsidies and transitioning away from fossil fuels, inter alia, by taking account of downstream consequences and regulating in a manner that does not undermine global co-operation.” There is also some critique about the hesitation of the unanimous opinion to go beyond saying that harm to others is not allowed to also say who is more vulnerable to harm and who is causing the harm.
To watch the judgement, go to: THE HAGUE – The International Court of Justice (ICJ) delivers its Advisory Opinion on the Obligations of States in respect of Climate Change | UN Web TV See also: https://www.volkskrant.nl/buitenland/internationaal-gerechtshof-landen-zijn-verplicht-alles-te-doen-tegen-beangstigende-klimaatverandering~bfa58eb0/