Fragmentation Remains Out There

In her opinion, Marìa Santillán argued that the recent Advisory Opinions of ITLOS, IACtHR, and the ICJ “mark a definitive shift from legal fragmentation toward a harmonized framework for state climate obligations.” She elaborates by debating that the “law of the sea and human rights law traditionally operated on separate tracks” and that the climate crisis “threatens marine ecosystems and human rights simultaneously, demanding an integrated legal response.” Moreover, she discusses that by building upon one another’s findings the Courts constructed “a cohesive legal order through systemic integration.”

In this short contribution, I propose two comments in response to Santillán’s post. First, while systemic integration is a desirable interpretative technique when legal reasoning involves multiple treaty regimes, not every interaction between distinct regimes per se requires its application. There should be an element of incompatibility between them, or as the ILC Fragmentation Report puts it, conflict-avoidance techniques apply when “the relevant treaties seem to point in different directions in terms of their application by a party” (para. 23). In my view, this is not the case in the examples mentioned in Santillán’s post. Second, although the Courts concurred on the principle of systemic integration as an interpretative approach, there remains a certain degree of divergence in its application, particularly with respect to principles such as lex specialis, Common But Differentiated Responsibility and Respective Capabilities (CBDR-RC) and Sustainable Development.

Pointing in Different Directions

The ILC Report on Fragmentation observes that the phenomenon of specialized legal regimes gives rise to “problems of coherence in international law” (para. 15). It further explains that “]t[his report examines techniques to deal with conflicts (or prima facie conflicts) in the substance of international law” (para. 21). In this context, the Commission understood a conflict “as a situation where two rules or principles suggest different ways of dealing with a problem” (para. 25).

In my view, the examples analyzed, namely the principles addressing marine pollution under UNCLOS, and their repercussions under human rights law and environmental law principles, do not, in fact, point in different directions. Rather, they do complement one another. For instance, highlighting the adverse human implications arising from marine pollution, concurrently conceived as environmental harm, is already embedded in both the UNCLOS framework and the human rights regime. This complementarity is also reflected in other instruments, such as the 2024 Human Rights Council’s Report of the Special Rapporteur on the promotion and protection of human rights in the context of climate change, which Marìa Santillán also cites (A/HRC/56/46, para.17).

This is not to suggest that I downplay the significance of systemic integration in areas where no apparent conflict exists. On the contrary, it remains both necessary and valuable, as it reinforces the relevant principles, enhances their systemic application, and promotes the overall protection of the rights at stake. Rather, while the Courts have meaningfully complemented one another in interpreting these mentioned principles, they have not, in fact, harmonized conflicting principles. Moreover, the Courts, particularly the ICJ and ITLOS, have overlooked certain areas of genuine conflict and, in some instances, have diverged from the IACtHR in precisely those contexts where greater integration would have been most warranted.  For instance, in its Advisory Opinion, the IACtHR adopted sustainable development as a general principle that informs both environmental and human rights regimes (para. 213). Such systemic interpretation was omitted by the ICJ and ITLOS, as further illustrated below. Another example concerns Maritime entitlements and the consequences of sea-level rise. Although ITLOS would have been the appropriate forum to discuss this issue, the Tribunal entirely avoided doing so, relying on a restrictive understanding of the Commission’s request (para. 150). A further point of reticence and divergence appears in the protection of nature. While the IACtHR explicitly recognized nature as a “subject of rights” under the sustainable development framework (paras. 279, 280), this recognition was entirely absent from the Opinions rendered by the ICJ and ITLOS.

Fragmentation Remains Out There

To clarify my argument in this section, I do not claim that the law of the sea, human rights law, and environmental law operate in perfect harmony. Rather, my argument is that certain areas urgently require systemic integration – yet the Courts have been too conservative in meaningfully engaging with them. Moreover, the Courts’ approach to certain principles, such as sustainable development and CBDR-RC, reveals a certain degree of divergence that might generate adverse implications in future contentious cases. It is insufficient for a Court to merely declare its commitment to systemic integration or to assert that it interprets obligations across regimes as part of a single legal system; this commitment should also be consistently reflected throughout the Court’s reasoning.

One of the fragmentary areas that calls for greater judicial engagement is the relationship between environmental law, international trade and investment law. The ICJ entirely avoided addressing this question, confining its reasoning to the laws it deemed “most directly relevant for answering question (a)]concerning the obligations of States to ensure the protection of the climate system from anthropogenic GHG emissions[”. Although the Court acknowledged that other rules of international law, such as international trade law and international investment law, might be relevant, it refrained from engaging with these branches of international law (para. 173). This caveat reflects a missed opportunity for the Court to confront a crucial issue of fragmentation: whether climate change norms could operate as lex specialis vis-à-vis potentially incompatible rules within the international investment law or WTO regimes. In line with its unduly cautious approach, the ICJ ultimately held that it “cannot find any actual inconsistency between the provisions of the climate change treaties and other rules and principles of international law that may be relevant for the response to question (a)” (para. 168). By excluding the international trade and investment law regimes and adopting a narrowly framed understanding of ‘conflict’, the Court made it easy to reach the conclusion that there is no “actual inconsistency” between the climate change treaties and other “relevant” applicable rules and principles of international law (para. 168).

By contrast, the IACtHR addressed the fragmentation between environmental obligations and international investment treaties in the context of the right to development. It held that international investment treaties are usually inconsistent with States environmental obligations as noted by the Expert Mechanism on the Right to Development of the United Nations Human Rights Council. The Court further concluded that there should be a balance which permits the regulatory policies adopted by States to address climate change, while protecting the legal certainty and predictability required for international investment agreements to incentivise foreign direct investment (para. 163). The approach adopted by the IACtHR represents a genuine example of systemic integration. While acknowledging the existing misalignment between the two regimes, the Court emphasized the need to strike a balance between the States’ right/obligation to adopt regulatory measures addressing the climate crisis and their duty to safeguard investors’ interests. Although the Court did not elaborate on how such a balance should be achieved, which would have been a valuable dictum, it nonetheless confronted the problem rather than avoiding it.

The principle of sustainable development, together with the related principle of CBDR-RC, constitutes another area in which the three Courts diverged in their approach. The IACtHR adopted a broad and integrated understanding of sustainable development, highlighting its dual function “as a path to securing the joint protection of human rights and the environment” (para. 213). This systemic conception is further reflected in the Court’s pronouncement that “the task of interpretation with which this Court has been entrusted on this occasion will be undertaken under the guidance not only of the principles inherent in the international protection of human rights […]; but also, taking into consideration fundamental principles and obligations in the context of the climate emergency such as [….], common but differentiated responsibilities […]” (para. 216) (emphasis added). This interpretative approach exemplifies the IACtHR’s willingness to integrate such a principle across regimes, thereby maximizing the potential benefits in both fields of human rights and environmental law.

Such a systemic approach towards the CBDR-RC principle was rejected by ITLOS on two occasions. First, the Tribunal held that “while the obligation under article 194, paragraph 1, of the Convention does not refer to the principle […] as such, it contains some elements common to this principle” (para. 229). Second, it found that articles 202 and 203 of UNCLOS do not refer to the CBDR-RC principle. Nevertheless, the obligation to assist developing countries according to those articles is correlated to the principle only in that developing States need assistance from the more developed (para. 326). This cautious and fragmented reading effectively deprives the CBDR-RC principle of its systemic potential, reducing it to a mere expression of technical assistance rather than a structural principle guiding the allocation of environmental responsibilities needed to achieve climate justice.

In a similar vein, the ICJ adopted a distinct approach to the CBDR-RC principle, holding that the latter constitutes a “core guiding principle for the implementation of the climate change treaties” and that it “reflects the need to distribute equitably the burdens of the obligations in respect of climate change” (para.148). It could therefore have been expected that the Court would seize this opportunity to elaborate on how such a “core guiding principle” generates specific obligations, and the possible consequences arising from their breach. However, the ICJ ultimately stressed that “]t[he principle […] does not establish new obligations but is relevant for the interpretation of treaties and the determination of rules of customary law relating to the environment” (para.151). In contrast to the IACtHR’s systemic approach, the understanding adopted by the ICJ and ITLOS confines the principle within the boundaries of the climate change regime. This narrow reading fails to reflect a genuinely integrative approach. Rather, it appears to weaken the principle’s normative force, limit its systemic potential, and further fragment its capacity to advance climate justice.

Conclusion

Systemic integration remains an essential technique to achieve the much-needed coherence and harmonization within an increasingly fragmented international legal order. Although the ICJ, ITLOS, and IACtHR might have converged on certain interpretative aspects of climate change rules in relation to other branches of international law in their recent Advisory Opinions, their overall approaches fall short of what could be described as “creating a powerful synergy where distinct legal regimes mutually reinforce one another”, as argued by Marìa Santillán. Moreover, the distinctness of legal regimes should not be conflated with fragmentation. The ICJ’s formal and conservative stance may be understandable given the institutional constraints and functions under which it operates. However, its restraint is not justified in all instances. Being a World Court, there remains considerable scope for it to advance and systematize its interpretative approach. By doing so, it could provide pathways for other courts and tribunals to further develop international legal protection, particularly in moments of urgency such as the ongoing climate crisis.