Symposium on the ICJ Climate Change Advisory Opinion: Carrying the Flag of the Progressive Development of International Law (Part II)

[Dr. Fabián Cárdenas is a Professor of international environmental law at Pontificia Universidad Javeriana]

The decision of 23 July 2025, issued by the International Court of Justice (ICJ), displays the progressive yet cautious trend recently adopted by this traditionally orthodox tribunal. With the banners of climate change, the Court, also carry the flag of the progressive development of international law, providing a fresh approach, not only to the topic itself, but to the way in which it intends to renew international legal discourses in the midst of a contemporary world characterized by political chaos and increasing legal indifference, particularly of those who boast power. Carrying the flag of climate change, the Court championed the progressive development of international law (defined by the ILC Statute as the preparation of new rules “on subjects which have not yet been regulated by international law or in regard to which the law has not yet been sufficiently developed in the practice of States”). 

We could certainly assure that, on the one hand, the world has a renewed and significantly more robust legal framework on climate change that will indeed strengthen and increase climate litigation around the world. On the other hand, it seems that we also count on a more open perspective on international law that not only smashes old theoretical ideas of fragmentation but also prepares approaches capable of reaching those who thought they could get away with it by being absent, evasive, and indifferent. In other words, the Court got rid of the idea that different branches of international law develop independently, causing overlaps and inconsistencies, as ICL studies have been arguing. Quite the opposite, the Court decisively reaffirmed the unity of international law as a whole and resolved possible conflicts through the idea of crosspollination of distinct fields. 

In part I, we tackled the specific contributions made by the Court amid these historical advisory proceedings. In the following part, we present questions declined by the Court -all that was expected yet unfortunately missing-, as well as the implications of the decision as a whole, from a critical southern perspective. Needless to add that these two posts, rather than solving the debate, only aim at opening it up for further and deeper analysis.  

Questions Declined

Undoubtedly, the ruling by the Inter-American Court of Human Rights and the International Tribunal for the Law of the Sea significantly influenced the ICJ’s decision. Among highlighted aspects are the customary obligation to prevent significant environmental harm, the inseparable link between human rights and environmental protection, the need to utilize the “best available science,” and “strict due diligence.” Nonetheless, notably absent were elements that the Inter-American Court of Human Rights took into account, but the ICJ omitted. These include:

The ICJ did not explicitly identify certain legal principles as ius cogens just as the ICHR did (ICHR Opinion, para. 287). It acknowledged the IPCC’s scientific validity but overlooked indigenous communities’ traditional knowledge. It did not address the rights of human rights and environmental defenders as depicted by the Escazu Agreement. The Court also failed to explicitly recognize the precautionary principle, the common but differentiated responsibilities principle, and the polluter-pays principle as customary international law (though it indirectly gave them legal value as criteria for assessing strict due diligence). It did not elaborate on international organizations’ climate obligations, including those participating in proceedings. It provided limited guidance on multinational corporations’ responsibilities regarding climate change, aside from stating states’ obligations to regulate corporate activities. It did not establish criteria for identifying or measuring environmental harm, nor did it clarify evidentiary boundaries of shared legal responsibilities. It also did not specify implementation phases, timelines, or concrete plans to achieve the revised temperature target of 1.5°C. Additionally, the Court completely overlooked the recognition of nature as a subject of rights, a fundamental international legal contribution recalled from judicial experiences in countries such as Colombia, New Zealand, Bangladesh, Ecuador, Bolivia, as well as the Inter-American system, and which are explored in detail in our book Standing for Nature – 2025. Furthermore, the ICJ scarcely references the principle of Sustainable Development, despite previously recognizing it as custom in the 2010 Pulp Mills case, which we argue, constitutes the contemporary legal paradigm, as elaborated in our book Derecho y Sostenibilidad – 2025, as well as in our paper “The path towards a new paradigm” – 2025.

All that was omitted by the Court could indeed have profound implications in international law; however, I believe that such a deeper analysis would require a further publication since the present one aims at opening the academic discussion regarding the climate change advisory opinions. 

Opinion’s Implications 

This ruling is not merely about morals, as incorrectly stated by some international actors. We surely know that advisory opinions are not legally binding per se as confirmed by the Court itself since the 1950 Advisory Opinion on the Interpretation of Peace Treaties with Bulgaria, Hungary and Romania (p. 10). However, this decision codifies and systematizes binding law. Hence, while the decision itself is non-binding, all its content references binding international law. This unprecedented development necessitates that international as well as domestic normative systems adapt to the parameters set by the advisory opinion, prompting significant structural changes, requiring national legislatures to implement these standards, national judges to apply them in adjudication, as well as governments to promote policymaking with a view to implementing the set objectives.  

As stated previously, legislatures around the world must act. They must ensure the elimination of incompatible norms and introduce new laws aligning with these international developments, setting standards. This requires legislative innovation, regulatory adaptation, budgetary allocation, and institutional mobilization to realize these objectives. Additionally, international relations must be seriously and technically managed. Such global commitment should be taken earnestly also by all multilateralism institutions, both at the regional and international levels. We believe that states from the global south, such as Colombia, for instance, who only contributes 0.5% of global greenhouse gas emissions, must assert Common but Differentiated Responsibilities, demanding wealthier countries’ historical obligations while defending their right to socio-economic development to effectively address environmental challenges. While the international community as a whole possesses a common interest in managing the climate crisis, not every State has the same amount of responsibilities. Developing states must certainly carry the greatest burden, not only because they have more resources -including financial, technical, and technological-but because their state of development is due to their highest historic responsibility caused by their much larger contribution to the earth’s depletion. It’s not help; it’s debt. That’s what the Global South wants the rest to acknowledge.     

Moreover, although the ICJ is well known for being rather cautious and attached to its traditions, I nevertheless deem this advisory opinion to be even more overreaching and avant-garde than we expected. It emphasizes the unity of international law, explicating the interdependence of environmental law, human rights law, the law of the sea, and other relevant fields. It sends a clear message to those States that have intentionally been avoiding environmental obligations that they cannot escape from this common global crisis, it sets a unified stricter goal of not getting beyond 1.5 C, it sets out defined parameters of stringency for the application of due diligence and makes clear that international law is not static at all but it is rather a dynamic social phenomenon that must be always keep in line with the world’s greatest challenges. In this case, the very survival of our species. Although in the South we are not very happy with the distribution of burdens as lightly referred to with the CBDR principle, we nonetheless accept the decision as an advancement. Nevertheless, it is both an explicit recognition and a clear regulation of the CBDR principle.     

This recent ICJ decision does not conclude the debate; it initiates it. Careful reading, internalization, and alignment with currently absent Foreign Legal and Environmental Policies are urgently required, more than ever.