Why today’s International Court of Justice (ICJ) Opinion on Climate Change matters for Our Oceans

oday’s Advisory Opinion from the International Court of Justice (ICJ) marks a pivotal moment for ocean protection and international environmental law. It acknowledges that greenhouse gas emissions are “unequivocally caused by human activities” and recognises that States must act urgently to address the “existential threat” of climate change. In a world grappling with the consequences of climate change, which has significant impacts on the health of our oceans, this presents a historic moment for ocean conservation. In this article, I highlight why this Advisory Opinion marks a historic moment for our oceans—though not the first of its kind, and explore some of the positive developments we can take from it.

Impact of Climate Change on Our Oceans

Climate-related marine harm includes ocean acidification, rising sea temperatures, habitat destruction, sea level rise, and coastal erosion. The retreat of mountain glaciers contributes to displacement of affected populations while further threatening food security, water availability, and livelihoods.

What Is an Advisory Opinion, and Is This the First?

Unlike an ICJ judgment on a case between States, an Advisory Opinion is a legal opinion given by a court at the request of a UN organ or specialised agency. It is not binding, but it is authoritative. It tells us how international law is understood by the court, and can shape future state behaviour, legislation, and advocacy. It can also help strengthen the positions of those seeking to hold governments and companies accountable.

The ICJ’s recent opinion follows similar moves from other courts. In May 2024, the International Tribunal for the Law of the Sea (ITLOS) issued its own Advisory Opinion, requested by the Commission of Small Island States, concluding that greenhouse gas emissions constitute marine pollution under the UN Convention on the Law of the Sea (UNCLOS). This was a major step in connecting the climate crisis to legal obligations at sea.

Similarly, the Inter-American Court of Human Rights (IACtHR), in its 2017 Advisory Opinion on environmental protection, clarified that states can have extraterritorial obligations– meaning they may be responsible for human rights harms beyond their borders, even without effective control over a territory, if the harm is foreseeable and originates from their conduct. This was an early endorsement of a now-growing trend in international legal thinking: moving from control-based to impact-based State accountability.

Key Legal Findings of the ICJ Advisory Opinion

1. Broad Legal Obligations: The Court confirmed the existence of numerous obligations to address climate change spanning multiple bodies of international law, including key treaties such as UNCLOS (sometimes referred to as the “constitution for the law of the sea”) (paras. 123-124).
2. Clean, Healthy and Sustainable Environment as Precondition to Human Rights Enjoyment: The Opinion affirms that a clean, healthy, and sustainable environment is essential for the enjoyment of international human rights. Main human rights treaties, including the ICCPR and ICESCR, include several rights relevant to ocean-based activities, such as the right to life, work, food, and labor rights like freedom of association. This legal recognition strengthens a growing global consensus and supports climate litigation efforts (paras. 388-393).
3. Obligation to Prevent Significant Harm: Under customary international law, the ICJ confirms that States are obliged to prevent significant harm to the environment, including to the environments of other States (para. 132). The duty to cooperate on climate action is also confirmed as a binding norm of international law, underscoring that climate-related harm must now be seen as a shared legal challenge (paras. 140-142).
4. Clarifying Causation in Climate Cases: The Court addressed the concept of causation, which is absolutely key for any legal argument. While acknowledging that the causal link between State conduct and climate harm can be more complex than with local pollution, the Opinion clarified that “identification of a causal link is not impossible in the climate change context; it merely means that the causal link must be established in each case through an in concreto assessment” (para. 438).

A Note of Caution

I wouldn’t be me if I didn’t add some nuances to all that positive news. Because as always, despite this positive legal momentum, I think it is important to be aware of some practical challenges:

• Non-Binding Nature: Advisory Opinions do not force governments to act. Their strength lies in shaping expectations, driving policy reforms, and providing advocacy tools, rather than direct enforcement.
• Implementation Gaps: Even well-established legal doctrines, such as extraterritorial obligations, are often ignored or weakly enforced. Most glaringly obvious in the case of the ongoing genocide in Palestine. This highlights the limits of law in the absence of political will and effective accountability mechanisms.
• The Need for Multi-Level Pressure: Turning legal theory into practical safeguards will require political leadership, climate litigation at all levels, and persistent public scrutiny.

Stay tuned for our next article focusing specifically on human rights at-sea! Coming this Friday.

Sources: ICJ Advisory Opinion of July 23, 2025 (case 187); International Tribunal for the Law of the Sea (ITLOS), Advisory Opinion, Request for an Advisory Opinion Submitted by the Commission of Small Island States (Request No. 31), 21 May 2024.