The ICJ Gives ‘Common Concern’ Principle Legal Teeth

“For the first time, the world’s highest court clarified that cooperation on climate change isn’t politics or diplomacy. It is the law,” writes Ye-Eun Uhm, an attorney and professor of international law at Ajou University.

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By Ye-Eun Uhm

International lawyers have long wrestled with an elusive phrase: climate change is a “common concern” of humankind. 

It first appeared in 1988, when the United Nations General Assembly Resolution (43/53) formally declared that climate change threatened all of humanity and had to be addressed collectively. The phrase found its way into the climate treaties that followed, including the UNFCCC and later the Paris Agreement. 

For decades, it remained more symbol than substance—diplomatic wallpaper, a polite preamble with little real bite. The International Court of Justice (ICJ) has now breathed new life into it.

From Vague Beginnings to State-Centered Limits

Until recently, the common concern principle was almost entirely – and unambitiously – shaped by states. “Common concern” was mostly code for “let’s cooperate when convenient.” In practice, common concern functioned as a political premise, not a binding ecological or legal standard. 

International lawyers also tended to describe the principle as it existed, rather than reimagining its potential. Much of the literature framed “common concern” in terms of state-to-state cooperation, but lacked analysis of its legal consequences or its relevance for non-state actors. Without a clear definition, states fell back on vague duties of cooperation.

What the ICJ Said

In its recent 140-page opinion on states’ obligations in respect of climate change, the ICJ mentioned “common concern” 11 times—and not just in passing. 

The court affirmed the phrase as a legal principle with concrete implications. It declared climate change a common concern of humankind and tied it directly to states’ customary obligations, namely the duty to co-operate for the protection of the environment (para 308). 

This is a monumental shift. For the first time, the world’s highest court clarified that cooperation on climate change isn’t politics or diplomacy. It is the law.

Due Diligence, Not Discretion

The Court also stressed that the duty to cooperate is judged by due diligence. In other words, it is not enough for states to show up at conferences or submit emissions reduction plans that look good on paper. What matters is how they cooperate—whether their actions are diligent and progressive (paras 218 & 280-300). 

On Nationally Determined Contributions, the ICJ was blunt: they are not just procedural. They must reflect the highest possible ambition and be collectively capable of meeting the 1.5C target (paras. 237-249). That language gives advocates and negotiators a powerful new lever. Weak pledges can now be called out not only as bad policy but also as a failure of legal duty.

Beyond States: Regulating the Private Sector

In paragraph 95, the court also clarified that states’ obligations extend beyond their own actions to include non-state actors under their jurisdiction or effective control. That means corporations, especially fossil fuel companies and heavy emitters, are now squarely in the frame. If they emit, states are responsible for ensuring that adequate regulations are in place to control those emissions. 

What is striking is that the court linked this directly to the UN General Assembly’s description of climate change as a “common concern of mankind”, adding that such a broad scope is particularly apt given the magnitude of the problem. The point is reinforced later, in paragraph 282, where the court stressed that states must adopt “appropriate measures that regulate both public and private operators.”

New Wave of Climate Lawsuits

The other sphere where the principle could prove powerful is civil society, particularly through legal action. Although advisory opinions are not binding, they often set interpretive baselines that ripple through domestic and international law. 

By affirming that climate change is a common concern, that states have concrete obligations to cooperate and exercise due diligence, and that these obligations extend to the conduct of non-state actors within their jurisdiction, the ICJ has given lawyers, activists, and ordinary citizens new hooks for litigation.

More on the topic: Climate Litigation No Longer a ‘Niche Concern’, 226 New Cases Filed in 2024: Report

A New Dimension

Common concern always carried more potential. The ICJ has now marked the beginning of that shift. When the UN first acknowledged the concept in 1990, it highlighted the effects across three dimensions: spatial, temporal and social. They stated that climate damage crosses national borders; its effects last for multiple generations; and addressing it requires action from all parts of society – including governments, courts, businesses, those in academia, and the public.

For decades, those broader possibilities were left underdeveloped. By affirming common concern as a legal obligation, the advisory opinion brings those dimensions back into view.

It means lawmakers must legislate not just for their own citizens but also in recognition of shared global duties, especially given the disproportionate climate impacts in developing countries and Small Island Nations. Courts can turn the principle into enforceable standards of cooperation and due diligence. Companies are accountable not only for domestic compliance but also for their contribution to a collective crisis. And at every turn, citizens can press governments and industries to honor obligations under international law.

Taken together, these shifts make clear that while states remain the primary duty-bearers, climate change cannot be addressed by states acting in isolation. Their conduct unfolds in the broader arena of global climate governance—subject to scrutiny and reinforced by parallel action from diverse actors.

Way Forward

The common concern principle is not confined to climate change. Rather, it is embedded in the Convention on Biological Diversity and can also extend to other transboundary environmental challenges, such as the ongoing plastics treaty negotiations. By defining these matters as common concern, international law gives rise to corresponding obligations that frame how state and non-state actors must respond.

The principle is now the code that defines adequate climate action and recognizes the role of every actor within global governance. The ball is now in our court: to use that guidance to demand greater accountability from those complicit in the climate crisis.

Featured image: UN Photo/ICJ-CIJ/Frank van Beek. Courtesy of the ICJ.

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About the author: Ye-Eun Uhm is an adjunct professor of international law at Ajou University and a diplomacy associate at Solutions for Our Climate. She is a New York-licensed attorney with an LL.M. and S.J.D. in international environmental law from American University Washington College of Law. Ye-Eun’s career has focused on sustainability, with experience across consulting firms, international organizations, and the nonprofit sector.