The climate crisis is not only an environmental and scientific emergency – it is a fundamental legal and ethical challenge. Nowhere is this more evident than in small island developing states (SIDS), which face the most immediate and severe consequences of global warming. Rising sea levels, saltwater intrusion, extreme weather events, and ecosystem collapse pose an existential threat to these nations, many of which contribute minimally to global greenhouse gas emissions. Yet, these vulnerable states have emerged as moral and legal leaders in global climate governance.
Their leadership was recently recognized through the historic advisory opinion issued by the International Court of Justice (ICJ) in July 2025. The opinion, which addresses the legal obligations of states in relation to climate change, was the result of a concerted effort led by small island states like Vanuatu and Tuvalu. This essay examines the legal strategy and diplomatic leadership of these states, the arguments presented during the ICJ proceedings by various countries, and the significance of the Court’s judgment in the evolving landscape of international climate law.
Why the Small Island States Turned to the ICJ?
Small island states have long sought stronger global climate action through political and diplomatic means. However, frustrated by the slow and often inadequate pace of international negotiations under the United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Agreement, they turned to international law as a more robust and principled avenue. Recognizing the urgency of their situation, SIDS spearheaded a campaign – supported by youth movements, civil society groups, and sympathetic states – to seek an advisory opinion from the ICJ.
The legal questions posed to the Court focused on two key issues: what obligations do states have under international law to protect the climate system for present and future generations, and what legal consequences arise when states fail to fulfil these obligations. The aim was not to assign blame or seek compensation directly, but to clarify the scope of existing legal duties and to reinforce the principle that climate inaction is not merely a policy failure but a breach of international law.
Legal Arguments by Small Island States and their Allies
The submissions presented by small island states and a wide range of supporting countries were grounded in a multidimensional legal framework. First, they invoked the customary international law principle of preventing transboundary environmental harm. This well-established norm obligates states to ensure that activities within their jurisdiction do not cause significant damage to the environment of other states. The argument was made that emissions of greenhouse gases, which contribute to global climate disruption, clearly fall within the scope of this principle.
Second, the Law of the Sea was cited as a foundational source of state obligations. Under the United Nations Convention on the Law of the Sea (UNCLOS), states have a duty to protect and preserve the marine environment. The argument was that climate change – through ocean warming, sea level rise, and acidification – constitutes a form of marine pollution. Accordingly, states that contribute significantly to climate change are failing to uphold their legal obligations under UNCLOS.
Third, the submissions relied heavily on international human rights law. It was argued that climate change directly undermines a range of fundamental rights, including the rights to life, health, housing, food, and cultural integrity. Treaties such as the International Covenant on Civil and Political Rights and the Convention on the Rights of the Child were invoked to support the claim that states must prevent foreseeable harms caused by climate change. The human rights framing also emphasized the importance of intergenerational equity – the idea that legal obligations extend not only to current citizens but also to future generations.
This comprehensive legal approach presented climate change as an issue that intersects with environmental, human rights, and maritime law. It underscored the idea that states have a collective and individual responsibility to act, and that failure to do so can result in legal consequences.
Counterarguments by Major Emitters
In contrast to the expansive and integrated approach advocated by small island states, several major emitting countries took a more cautious and restrictive position. The United States, China, and several European nations argued that existing international climate agreements – particularly the Paris Agreement – already regulate state obligations. They contended that the Paris framework, based on nationally determined contributions (NDCs), was intentionally designed as a flexible and non-binding system that respects national sovereignty.
These states expressed concern that the ICJ might impose binding legal duties that go beyond what was negotiated under the Paris Agreement. They warned that such an outcome could create legal uncertainty, politicize climate diplomacy, and potentially disrupt ongoing international cooperation. Moreover, they argued that holding states legally accountable for historical emissions or for not meeting voluntary climate targets would be legally problematic and politically divisive.
Despite these reservations, a clear majority of states and international organizations supported the request for an advisory opinion. They argued that the gravity of the climate crisis, and the inadequacy of current mitigation efforts, justified a more authoritative legal interpretation of state responsibilities.
Influence of Other International Courts
The ICJ proceedings were informed by recent decisions from other international judicial bodies that have increasingly recognized the legal dimensions of climate change. Notably, the International Tribunal for the Law of the Sea (ITLOS) issued an advisory opinion in 2024 that classified greenhouse gases as marine pollutants under UNCLOS. This ruling established that states have an obligation to take all necessary measures to reduce such pollution and to protect the marine environment.
Similarly, in 2025, the Inter-American Court of Human Rights delivered an opinion affirming the right to a healthy environment as a legally protected human right. This reinforced the growing body of jurisprudence linking environmental degradation with human rights violations. In Europe, the European Court of Human Rights, in the KlimaSeniorinnen case, found that Switzerland had violated the rights of elderly women by failing to implement adequate climate policies.
These judicial developments helped shape the ICJ’s understanding of the legal context and supported the argument that climate change implicates a broad range of state duties under existing international law.
The ICJ’s Advisory Opinion
On 23 July 2025, the ICJ delivered its long-anticipated advisory opinion, confirming that states have clear legal obligations under international law to address climate change. The Court held that these obligations arise not only under climate-specific treaties such as the UNFCCC and Paris Agreement but also under customary international law, the law of the sea, and international human rights law.
The Court affirmed that states must act with due diligence to prevent significant harm to the global climate system. This includes a duty to take concrete and timely measures to mitigate emissions and to cooperate internationally in climate response efforts. The ICJ also recognized that states bear responsibilities toward both present and future generations, reinforcing the principle of intergenerational equity.
Importantly, the Court found that failure to meet these obligations may entail legal consequences. While the opinion did not impose reparations or liability in a strict sense, it stated that breaches of international climate obligations could require states to take remedial action, to cease harmful conduct, and to prevent its recurrence. This aspect of the opinion provides a legal foundation for future litigation and accountability mechanisms.
The Strategic Leadership of Small Island States
The ICJ opinion is a testament to the strategic leadership of small island states. Despite their limited geopolitical power and financial resources, they were able to build a broad international coalition, frame the legal questions effectively, and navigate the procedural complexities of the ICJ. Their success was grounded in a sophisticated understanding of international law and a compelling moral narrative centered on survival, dignity, and justice.
Small island states demonstrated that even the most vulnerable actors in the international system can influence global legal norms. They also showed how legal tools can be used not just defensively, but proactively, to shape the rules of the game and to compel more powerful actors to act with responsibility.
Implications for Global Climate Governance
The ICJ’s advisory opinion will likely have wide-ranging impacts. It is expected to influence national courts considering climate-related cases, bolster the credibility of climate litigation brought by civil society and affected communities, and guide the development of more stringent international agreements. The opinion also supports ongoing efforts to establish “loss and damage” financing mechanisms within the UN climate process, by affirming that states have obligations to assist those suffering irreversible climate harms.
More broadly, the opinion shifts the narrative around climate change. It reinforces the view that climate inaction is not merely a failure of politics, but a violation of international law. It elevates the moral and legal urgency of climate action and provides a platform for more equitable and effective global governance.
Conclusion
The 2025 advisory opinion of the International Court of Justice represents a pivotal moment in the legal recognition of climate change as a matter of international obligation. It affirms that states must act to prevent environmental harm, protect human rights, and uphold their duties to future generations. This achievement would not have been possible without the vision and determination of small island states, whose advocacy transformed the global legal landscape.
By turning to the law, these states have reframed climate change as a matter of justice, accountability, and survival. Their efforts serve as a powerful reminder that those most affected by global crises can also be the most effective advocates for transformative change. As the world continues to confront the challenges of a warming planet, the leadership and legal ingenuity of small island states will remain a beacon for equitable and just climate governance.