The Common Concern of Humanity: Has the ICJ Advisory Opinion on Climate Change Helped it “Cross into the Kingdom of Law”?

[Omar Grech is Associate Professor within the Department of International Law, University of Malta]

Several excellent posts on this blog have already explored different facets of the ICJ’s Advisory Opinion on Climate Change, including its treatment of state responsibility and obligations erga omnes. This post takes a different tack. It argues that the Opinion marks a doctrinal breakthrough for the concept of the common concern of humanity (CCH), a notion long present in treaty preambles and scholarly debate but rarely given legal force.

For decades, the concept has floated in the preambles of treaties and the pages of scholarship — normatively appealing but legally unsettled. With this Opinion, the UN’s principal judicial organ has for the first time integrated CCH into the very structure of its reasoning, nudging the concept across the line from rhetorical affirmation toward juridical consolidation.

This post situates the ICJ’s Opinion within the longer genealogy of CCH and argues that it represents a doctrinal shift. Whereas earlier courts treated CCH implicitly or rhetorically, the ICJ used it as a legal principle to shape obligations erga omnes, treaty interpretation, and human rights protection. The result is the elevation of CCH from aspirational idea to potential bridge norm in international law.

A Short Genealogy of CCH

The idea that climate change is a matter of common concern dates back to Malta’s initiative at the UN General Assembly in 1988, resulting in Resolution 43/53. The UNFCCC (1992) and later the Paris Agreement (2015) reiterated the language, declaring climate change a “common concern of humankind.” Similar formulations appear in the Convention on Biological Diversity and other instruments.

Yet for decades these references remained largely preambular. Scholars and states worried about sovereignty, enforcement, and doctrinal clarity. As Judge Manfred Lachs put it at a meeting of legal scholars held in Malta in 1990, CCH had not yet “crossed the threshold into the kingdom of law.”

A Typology of Judicial Engagement

To assess how courts have handled CCH, we can distinguish three types of engagement, which may be summarised into three broad categories: (i) implicit engagement: where the reasoning of the court is consistent with CCH without naming it; (ii) rhetorical engagement ehere the court explicit mention CCH without a direct legal consequence; and (iii) doctrinal engagement: where the court integrates CCH into the operative reasoning.

This typology helps explain the uneven jurisprudential trajectory of CCH. In Urgenda v. Netherlands, the Dutch Supreme Court imposed binding mitigation duties on the state, reasoning in line with CCH’s logic of collective responsibility — but without naming it. The UN Human Rights Committee in Torres Strait Islanders v. Australia (2022) and the German Constitutional Court in Neubauer (2021) adopted similar reasoning, linking climate harms to rights and intergenerational equity, but again avoided the terminology.

By contrast, the ITLOS Advisory Opinion on climate change (2024) explicitly recalled that climate change is a “common concern of mankind,” but treated it largely as context — a rhetorical rather than doctrinal move. The real breakthrough came when the European Court of Human Rights in Verein KlimaSeniorinnen Schweiz v. Switzerland (2024) held that insufficient climate action violated rights under the ECHR. The Court invoked CCH to expand standing and interpret state obligations, marking one of the first doctrinal deployments of the concept.

The ICJ has now gone further.

Doctrinal Integration 

In its 2025 Advisory Opinion, the ICJ repeatedly cited CCH and operationalized it across multiple registers. From a rhetorical perspective, the Court underscored the transboundary and intergenerational nature of the climate crisis. Normatively it utilised CCH to ground principles of cooperation and equity. Finally, from a doctrinal perspective interpreting treaties and obligations through CCH.

Most significantly, the Court linked CCH to obligations erga omnes partes. Recalling that the UNFCCC and Paris Agreement characterize climate change as a “common concern of humankind,” the Court concluded that the obligations under these treaties safeguard an essential interest of all states and therefore carry erga omnes character.

This is no small move. By embedding CCH into the interpretive framework of treaty and customary law, the Court positioned it as a structural principle of international law. While it stopped short of declaring CCH a binding rule of custom, the Opinion sets a new benchmark: climate stability is not just a political priority but a legal concern of all states.

CCH as a Bridge Norm

The ICJ’s Opinion also reframes CCH as a bridge norm. Rather than being siloed in environmental law, it now connects climate treaties such as the UNFCCC and Paris Agreement with human rights law, where the protection of life, health, housing, and other fundamental interests are directly threatened by climate instability, and with general international law, particularly the erga omnes obligations and the duty to cooperate. In doing so, the Court strengthens CCH’s consolidative potential. It is no longer merely a preambular flourish, but a concept that organizes legal reasoning across different regimes.

This bridging function is significant. By drawing human rights explicitly into the ambit of climate law, the Court acknowledged that climate stability underpins the enjoyment of core rights. That interpretive move opens the door for future litigants to argue that failures in mitigation or adaptation constitute violations of internationally protected rights, not just breaches of environmental commitments. Situating CCH within the framework of obligations erga omnes likewise elevates climate duties to the level of foundational norms owed to the international community as a whole. Taken together, these moves suggest that CCH may evolve into a general principle of international law, providing a common vocabulary that links fragmented regimes and fosters coherence across treaty law, human rights adjudication, and domestic constitutional orders.

Missed Opportunities

Not all courts have taken the same step. The Inter-American Court of Human Rights, for example, in its recent climate advisory opinion aligned with the logic of CCH but avoided the term. The German Constitutional Court and Colombian Supreme Court likewise drew on its logic without naming it.

This terminological inconsistency matters. As early critics such as Judge Lachs warned, uneven usage risks diluting legal coherence. The ICJ’s Opinion is therefore significant not only for its substantive conclusions but also for its contribution to terminological consolidation. If other courts follow its lead, CCH may crystallize more fully as a general principle.

Conclusion: A New Benchmark?

The ICJ has shifted the terrain. For the first time, the common concern of humankind is not just a political slogan or a preambular statement, but part of the juridical infrastructure of international law.

Whether this marks the beginning of CCH’s crystallization into binding customary law remains to be seen. But by linking it to erga omnes obligations, situating it at the crossroads of environmental, human rights, and general international law, and explicitly naming it as such, the Court has provided a doctrinal anchor for future courts and litigants.

From Malta’s proposal in 1988 to The Hague in 2025, the journey of CCH reveals how concepts evolve in international law: from political aspiration, to rhetorical device, to legal principle. The ICJ’s Advisory Opinion sets a new benchmark in that trajectory — one that future jurisprudence will either build upon or erode. For now, the common concern of humankind stands closer than ever to becoming a general principle of international law.