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The ICJ's Landmark Advisory Opinion on Climate Change: An Opinion that matters…
by Dr Louise Smail
On the 23rd of July, the International Court of Justice (ICJ)[1] issued a unanimous advisory opinion in response to questions posed by the UN General Assembly regarding the obligations of states in respect of climate change. This advisory opinion can be seen as a way of looking at states' legal obligations and responsibilities concerning climate change. Although the ICJ's advisory opinions are not legally binding and the Court cannot compel countries to abide by its findings it could be argued that a Governments' failure to act on climate change could be considered to be a breach of law, with potential legal, financial, and diplomatic consequences.
As can be read in the book Climate Change Law and Practice, from the number of legal cases already going through the courts internationally, this advisory opinion could have significant implications. The question is whether the threat of exposure to litigation in national courts will force governments to urgently reduce emissions and demonstrate their compliance with treaty negotiations. This opinion comes months before COP30, scheduled for November in Brazil.
Key Findings of the Opinion
The opinion finds that international law on climate change is derived from multiple sources, including climate change and environmental treaties, international human rights law, and customary international law. It lays out several significant findings:
Kyoto Protocol: State parties must act with due diligence to fulfil the commitments made in the protocol, including common but differentiated responsibilities for high emitters.
Paris Agreement: State parties are obliged to prepare, communicate, and maintain nationally determined contributions (NDCs) which, when taken together, can contain global warming to 1.5°C above pre-industrial levels.
Responsibility of States: The International Law Commission's Articles on Responsibility of States for Internationally Wrongful Acts (2001) applies to climate change law, increasing certainty when pursuing remedies for environmental harms that cross borders.
Duties to Prevent Harm and Cooperate: The opinion enshrines two duties: to prevent significant harm to the environment and to cooperate internationally. These duties are customary law, applicable to all states regardless of their signatory status with climate change treaties.
Whilst the advisory opinion lacks binding force, the opinion can be seen as an authoritative interpretation of law and has the potential to reshape global climate governance as a tool of 'preventive diplomacy'. The legal principles clarified in the opinion are binding as part of international law. For example, it clarifies the core principles of attribution and causation in meeting legal obligations to prevent harm. The opinion serves as a signal to governments that national and regional policies should align with evolving international legal norms.
The opinion expands countries' legal exposure by confirming that all states have binding duties regardless of their participation in climate treaties. However, the question whether this will apply to the US after its withdrawal from the Paris agreement remains to be seen. For businesses, the opinion stops short of creating direct obligations under international law but confirms the duty of states to regulate private companies more effectively.
The ICJ's advisory opinion on climate change represents a significant step forward in the global effort to address climate change. By clarifying state responsibilities and expanding legal exposure, the opinion has the potential to influence future treaty-making, shape climate-related litigation, and strengthen global climate governance. At COP30, the opinion provides a crucial tool for smaller countries to demand accountability and action from high-emitting nations. The ICJ's opinion underscores the importance of aligning national and regional policies with evolving international legal norms and highlights the need for urgent and sustained action to combat climate change.
[1] OBLIGATIONS OF STATES IN RESPECT OF CLIMATE CHANGE
https://www.icj-cij.org/sites/default/files/case-related/187/187-20250723-adv-01-00-en.pdf
