On 23 July 2025, the International Court of Justice (ICJ) issued a landmark Advisory Opinion regarding the “Obligations of States in Respect of Climate Change.” This opinion was delivered in response to a request from the United Nations General Assembly (UNGA) and was unanimously adopted. It clarifies the existing international legal obligations of states to protect the climate system from anthropogenic greenhouse gas (GHG) emissions and the legal consequences for failing to meet these obligations.

The main aspects highlighted in the responses focus on the obligations of States under international law to protect the climate and environment from anthropogenic greenhouse gas emissions. The responses emphasise the broad legal framework considered, including the UN Charter, climate treaties, human rights instruments, and general principles such as sustainable development, equity, and precaution. They also discuss the recognition of these obligations as erga omnes, meaning they are of interest to the entire international community, and outline the legal consequences for States that fail to meet their obligations, including cessation, non-repetition, and full reparation. Additionally, the responses note the challenges of attributing responsibility due to the collective nature of emissions, but affirm the possibility of scientific attribution and the need for case-by-case assessment. The integration of human rights considerations into climate obligations is also underscored, with the ICJ limiting its role to identifying general obligations and consequences rather than resolving specific disputes or predicting future legal developments.

The ICJ confirmed its authority and discretion to issue the opinion, highlighting the “unprecedented challenge of civilizational proportions” posed by climate change. It extensively referenced the Intergovernmental Panel on Climate Change (IPCC) reports as the “best available science” regarding the causes and consequences of climate change, affirming that human activities unquestionably cause global warming and result in “widespread adverse impacts and related losses and damages to nature and people.”

Key takeaways include:

Comprehensive Legal Framework: States’ obligations derive from a broad spectrum of international law, including the UN Charter, climate change treaties (UNFCCC, Kyoto Protocol, Paris Agreement), UNCLOS, other environmental treaties, customary international law, and international human rights law. The principle of lex specialis does not generally exclude the application of other rules of international law.2)

Stringent Due Diligence: The duty to prevent significant environmental harm, a customary international law obligation, applies to the climate system and requires a “stringent” standard of due diligence, accounting for scientific information, relevant international rules, and states’ differentiated capabilities.

Paris Agreement Obligations: The Paris Agreement sets a primary temperature goal of limiting global warming to 1.5°C above pre-industrial levels. States have an obligation to prepare, communicate, and maintain “successive and progressive nationally determined contributions (NDCs)” that reflect their “highest possible ambition” and, when taken together, are “capable of achieving the temperature goal.” States are also obliged to “pursue domestic mitigation measures” with due diligence.

 Co-operation as a Legal Obligation: The duty to co-operate for environmental protection is a customary international law obligation, reinforced by treaties, and is “not a matter of choice for States but a pressing need and a legal obligation.” This includes financial assistance, technology transfer, and capacity-building.

Sea Level Rise and Statehood: The Court clarified that UNCLOS does not obligate states to update their maritime baselines and outer limits in response to climate change-related sea level rise. Furthermore, the “disappearance of one of its constituent elements would not necessarily entail the loss of its statehood” for an established state.

 Human Rights Linkage: The Court explicitly recognised that a “clean, healthy and sustainable environment is a precondition for the enjoyment of human rights,” and states have obligations under international human rights law to protect the climate system to ensure the effective enjoyment of rights like the right to life, health, and an adequate standard of living.

State Responsibility: Breach of any identified obligation constitutes an “internationally wrongful act” entailing state responsibility, including duties of cessation, non-repetition, and full reparation (restitution, compensation, satisfaction). The rules on state responsibility, including those on attribution and causation, are applicable in the climate change context, despite its complex and cumulative nature.

The ICJ’s Advisory Opinion underscores that international law provides a robust framework for addressing climate change, establishing clear and stringent obligations for states. While recognising the legal and scientific complexities, the Court emphasises that the crisis demands “human will and wisdom” beyond legal solutions, with the hope that its findings will “inform and guide social and political action to address the ongoing climate crisis”.

Carlos Torres