A long-standing conundrum of international environmental law is that the territorially-based, sectoral legal structures we have created to address environmental issues do not match the interconnected, interdependent nature of ecosystems. For many, this problem is writ large in the climate context. Whereas the science—synthesized in recent assessments and special reports by the Intergovernmental Panel on Climate Change (‘IPCC’)—emphasizes the deep interlinkages between issues of climate change, marine and terrestrial biodiversity loss, and ocean degradation, the international legal response is fragmented and uncoordinated. This gives rise to concerns of conflict and inconsistency between different international legal regimes, as well as the potential for ‘forum shopping’ in dispute settlement where different aspects of an environmental issue are presented to different judicial forums, which may reach differing conclusions on the interpretation of relevant international rules.
After many years during which international courts and tribunals have been largely silent on climate questions, 2024 has witnessed convergent advisory opinion proceedings taking place in three different bodies: the International Tribunal on the Law of the Sea (‘ITLOS’ or ‘Tribunal’), the International Court of Justice (‘ICJ’) and the Inter-American Court of Human Rights (‘IACHR’). On one view, this might seem to set the stage for the exacerbation of a fragmented international legal response, ‘undermining the foundations of future cooperation combating climate change’.
But the first international advisory opinion on climate change—delivered by ITLOS in its decision of 21 May 2024—suggests a more hopeful outcome. Although primarily tasked with elucidating the ‘specific obligations of State Parties to the United Nations Convention on the Law of the Sea (‘UNCLOS’), including under Part XII’, the Tribunal’s decision interweaves law of the sea requirements with those of other international laws relevant to climate change. In the process, the Tribunal illustrates how the fragmentation of international legal responses to climate change need not be seen as a weakness but could rather be a strength. The ITLOS advisory opinion crafts a series of interlocking and mutually reinforcing obligations across international climate law and international law of the sea that may ultimately serve to strengthen states’ duties to reduce greenhouse gas (‘GHG’) emissions and minimize the serious environmental harms resulting from climate change.
Unlocking UNCLOS as an Instrument of Climate Protection
When it comes to addressing the problem of climate change through international law, the global climate treaties—the 1992 United Nations Framework Convention on Climate Change (‘UNFCCC’) and the 2015 Paris Agreement—are undoubtedly the main game in town (see ITLOS advisory opinion, para. 222). But even from early on, they were not the sole locus of international climate law. The UNFCCC is applicable only to GHGs not controlled by the Montreal Protocol on Substances that Deplete the Ozone Layer and specific responsibilities for international aviation and maritime transport emissions are conferred on the International Civil Aviation Organization (‘ICAO’) and the International Maritime Organization (‘IMO’). As the significance of climate threats has increased and the science has firmed, climate change is increasingly addressed in other areas of international law, from human rights, to international humanitarian law and trade law.
In this regard, international law of the sea is not an obvious candidate as a major site for action on climate change. UNCLOS was concluded in 1982 before climate change became a prominent issue of international concern, and the treaty lacks express references to GHG emissions or climate impacts. As argued in some of the state submissions before ITLOS, this might have led to a conclusion that law of sea obligations should give way to those of the international climate regime in dealing with the question of states’ obligations to address the impacts of GHG emissions and resultant climate change on the marine environment (see ITLOS advisory opinion, para. 220).
Instead, the Tribunal, in its advisory opinion, uses a series of interpretive ‘keys’ to unlock the potential of UNCLOS as a climate protection instrument. These include:
- A ‘broad’ approach to interpreting treaty language and the scope of relevant provisions relating to protection and preservation of the marine environment; and
- Seeking to ensure coordination and harmonization between UNCLOS and ‘external rules’ to ‘clarify and inform the meaning of the provisions of the Convention and to ensure that the Convention serves as a living instrument’ (see ITLOS advisory opinion, para. 130 [and also Christina Voigt’s contribution to this series]). In particular, ITLOS’ reference to rules of international climate law allowed the Tribunal to draw conceptual links between the animating concepts of climate law and the law of the sea.
Broad Treaty Interpretation Approach
An illustration of the Tribunal’s ‘broad’ approach to interpretation of UNCLOS treaty language is found in its analysis of whether anthropogenic GHG emissions to the atmosphere can be considered ‘pollution of the marine environment’ for the purposes of UNCLOS. (The Tribunal adopted a similar approach in its interpretation of UNCLOS article 192 dealing with the obligation to protect and preserve the marine environment (see, e.g. ITLOS advisory opinion, paras 385, 388)). Although UNCLOS does not provide a list of pollutants or forms of pollution of the marine environment, the Tribunal found it provides (cumulative) criteria to determine what constitutes such pollution (see UNCLOS, Art. 1(1)(4)), namely:
‘(1) there must be a substance or energy; (2) this substance or energy must be introduced by humans, directly or indirectly, into the marine environment; and (3) such introduction must result or be likely to result in deleterious effects.’
ITLOS noted that this ‘definition is general,’ meaning that ‘it encompasses whatever satisfies these criteria’ (see ITLOS advisory opinion, para. 161). Taking each of these components to have a ‘broad’ or ‘ordinary’ meaning (see, e.g., ITLOS advisory opinion, paras 163, 171, 172) the Tribunal reached a conclusion that ‘anthropogenic GHG emissions into the atmosphere constitute pollution of the marine environment within the meaning of article 1, paragraph 1, subparagraph 4, of the Convention’ (see ITLOS advisory opinion, para. 179).
Coordination with the Rules of International Climate Treaties
The Tribunal’s use of rules under international climate laws—particularly the Paris Agreement—to craft a coherent framework of climate protection across those rules and requirements of the international law of the sea is perhaps most evident in its analysis of the obligation under Article 194(1) of UNCLOS to take all measures ‘necessary to prevent, reduce and control pollution of the marine environment from any source’.
Referring to Article 4(1) of the Paris Agreement, which sets the aim of reaching net zero GHG emissions in the second half of this century, ITLOS sees consistency between this aim and the objective of Article 194(1) of UNCLOS (ITLOS advisory opinion, para. 200). Moreover, while acknowledging that UNCLOS does not provide specific criteria as to what constitute necessary measures to address pollution of the marine environment, the Tribunal found coherence between the kinds of measures articulated as examples under UNCLOS provisions (e.g. Article 194(3)) and the ‘mitigation measures’ to reduce GHG emissions specified by the international climate regime (ITLOS advisory opinion, para. 205).
Finally, the Tribunal included ‘[i]nternational rules and standards relating to climate change’ among the ‘various factors States should consider in their objective assessment of necessary measures to prevent, reduce and control marine pollution from anthropogenic GHG emissions’ (ITLOS advisory opinion, paras. 207, 214 and 222). It identified the Paris Agreement’s temperature goal (Art. 2(1)(a)) and its ‘timeline for emission pathways’ (Art. 4(1)) as ‘particularly relevant’ for informing the content of ‘necessary measures’ addressing marine pollution (see ITLOS advisory opinion, paras 215 and 222).
Separate Obligations but Mutually Reinforcing International Laws
While ITLOS in its advisory opinion sought harmony between obligations under UNCLOS and the requirements of international climate law, it nevertheless staked out a clear space of operation for law of the sea provisions in addressing GHG emissions and marine-related climate impacts. In so doing, the Tribunal showed how the law of the sea can play a complementary role to reinforce global goals to reduce GHG emissions and minimize the impacts of climate change.
This approach came to the fore in the Tribunal’s consideration of arguments from some participants that compliance with the UNFCCC and Paris Agreement would satisfy the specific obligation under UNCLOS to take measures regarding pollution of the marine environment arising from anthropogenic GHG emissions, and that Part XII of UNCLOS should not be interpreted as imposing emissions reduction obligations that are inconsistent with, or go beyond, those agreed under international climate treaties (ITLOS advisory opinion, paras 219-220). As the Paris Agreement leaves to each party decisions about domestic targets and timelines for reducing GHG emissions, this reasoning would have left the adoption of ‘necessary measures’ for addressing GHG-related ocean pollution entirely within the discretion of individual states, which might ‘frustrate the very goal of [UNCLOS]’ to protect and preserve the marine environment (ITLOS advisory opinion, para. 224).
The ITLOS advisory opinion charts a different course. It finds that the obligation under Article 194(1) of UNCLOS cannot be satisfied ‘simply by complying with the obligations and commitments under the Paris Agreement’ (ITLOS advisory opinion, para. 223; see also paras 201-2). According to the Tribunal, the Paris Agreement and UNCLOS ‘are separate agreements, with separate sets of obligations’ (ITLOS advisory opinion, para. 223). Hence the relationship between the two is complementary as regards the obligation to regulate marine pollution from anthropogenic GHG emissions; ‘the former does not supersede the latter’ (ibid). Indeed, the requirements of Article 194(1) of UNCLOS impose a distinct legal obligation on states parties ‘to take all necessary measures to prevent, reduce and control marine pollution from anthropogenic GHG emissions, including measures to reduce such emissions’ (ibid). Accordingly, if a state fails to comply with this specific obligation, its international responsibility would be engaged (ibid).
Conclusion: A Holistic Vision of Climate-relevant International Law
In this ‘critical decade’ for climate action, it can be easy to see the multiplicity of international laws with potential relevance for addressing climate change as more of a hindrance than a help. Some states and commentators have expressed anxiety that seeking multiple advisory opinions on climate obligations from different international courts and tribunals will only exacerbate the complexity of the international legal landscape for climate protection. But by advancing a more holistic vision of climate-relevant international law—one that seeks to harmonise but also allow for complementary interaction amongst the obligations set under different regimes—the ITLOS advisory opinion offers hope. It holds out the promise of a synergistic international legal response to climate change that better maps to the integrated and interconnected nature the ecosystems at stake and to the multi-pronged regulatory effort that will be needed to safeguard our climate system.
Jacqueline Peel
Jacqueline Peel is a Professor of Law at the Melbourne Law School and Director of the multidisciplinary climate initiative, Melbourne Climate Futures, at The University of Melbourne, Australia. She served as a Lead Author on the IPCC’s 6th Assessment Report, Working Group III (Mitigation) and led the Hague Academy of International Law’s first-ever Centre for Studies and Research on Climate Change Law in 2022.
