ICJ AO Litigation Notes Digest

This guide, published by the Center for International Environmental Law (CIEL) in February 2026, provides a structured digest of key excerpts from the International Court of Justice's (ICJ) unanimous advisory opinion (AO) delivered on 23 July 2025 regarding States' obligations in relation to climate change. The document is designed as a practical tool for climate litigation practitioners to integrate the ICJ's normative clarity into domestic, regional, and international legal cases.

• The ICJ identifies the reports of the Intergovernmental Panel on Climate Change (IPCC) as the authoritative source of the 'best available science' and confirms that cumulative greenhouse gas (GHG) emissions are the primary cause of risks from anthropogenic climate change. The Court notes that fossil fuel combustion in energy conversion systems—including power plants, aircraft, automobiles, and home/business heating—accounts for approximately 64 per cent of CO2 emissions.
• The Court establishes that the 1.5°C threshold is the primary temperature goal for limiting global average temperature increase under the Paris Agreement. It asserts that Nationally Determined Contributions (NDCs) must reflect a party's 'highest possible ambition' and be capable of contributing to this temperature goal; the mere formal preparation of NDCs is insufficient for compliance.
• The ICJ rules that the applicable law for climate change is not limited to climate treaties but includes the UN Charter, UNFCCC, Kyoto Protocol, Paris Agreement, UNCLOS, the Biodiversity Convention, the Desertification Convention, international human rights law, and customary duties to co-operate and prevent significant environmental harm. The Court explicitly rejects the argument that climate change treaties constitute the only relevant law via the principle of lex specialis.
• The Court defines the 'duty to prevent significant harm' as a primary obligation applying to all States, regardless of treaty membership. This duty is measured by a 'stringent' standard of due diligence, which requires States to use all means at their disposal to avoid activities in their territory or jurisdiction that cause significant damage to the environment of another State. This includes the obligation to regulate both public and private operators and to conduct environmental impact assessments for activities with potential transboundary impacts.
• The ICJ concludes that obligations to protect the climate system from anthropogenic GHG emissions, specifically the customary duty to prevent significant transboundary harm, are obligations 'erga omnes' (owed to the international community as a whole). Consequently, all States parties have a legal interest in the main mitigation obligations of climate treaties and may invoke the responsibility of other States for failures to fulfill them.
• The Court recognizes the human right to a clean, healthy, and sustainable environment as essential for the enjoyment of other human rights, such as the right to life, health, and an adequate standard of living. It states that the protection of the climate system is a precondition for the enjoyment of human rights, and States must take mitigation and adaptation measures to guarantee these rights.
• Regarding legal consequences, the Court states that a State may be held responsible for failing to exercise due diligence in limiting emissions from private actors. Legal remedies include obligations of cessation (which may require revoking administrative or legislative measures), non-repetition, and full reparation. Reparation may take the form of restitution (e.g., restoring ecosystems), compensation for financially assessable damage, or satisfaction (e.g., formal apologies).

APA

Center for International Environmental Law (2026). ICJ AO Litigation Notes Digest. https://www.ciel.org/wp-content/uploads/2026/03/ICJ_AO_Selected-ICJ-AO-Excerpts-of-Overarching-Importance_Feb-2026.pdf

Chicago

Center for International Environmental Law. ICJ AO Litigation Notes Digest. 2026. https://www.ciel.org/wp-content/uploads/2026/03/ICJ_AO_Selected-ICJ-AO-Excerpts-of-Overarching-Importance_Feb-2026.pdf.

Wikipedia

{{cite report |author=Center for International Environmental Law |title=ICJ AO Litigation Notes Digest |date=February 2026 |url=https://www.ciel.org/wp-content/uploads/2026/03/ICJ_AO_Selected-ICJ-AO-Excerpts-of-Overarching-Importance_Feb-2026.pdf |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{centerforinternationalenvironmentallaw2026icj, author = {{Center for International Environmental Law}}, title = {{ICJ AO Litigation Notes Digest}}, institution = {Center for International Environmental Law}, year = {2026}, month = feb, url = {https://www.ciel.org/wp-content/uploads/2026/03/ICJ_AO_Selected-ICJ-AO-Excerpts-of-Overarching-Importance_Feb-2026.pdf}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }