Forging a Synergistic Path: Tackling Climate Change Through UNCLOS and Beyond


This week, the International Tribunal for the Law of the Sea (ITLOS) delivered its highly anticipated Advisory Opinion requested by the Commission of Small Island States (COSIS) on Climate Change and International Law. It marks a significant milestone in international climate change law, particularly in establishing and clarifying States’ obligations to reduce anthropogenic greenhouse gas (GHG) emissions affecting the marine environment. The Advisory Opinion holds importance for five key reasons, although its actual impact remains to be seen.

Firstly, the Advisory Opinion expands ITLOS’ jurisdictional basis for advisory opinion proceedings. Secondly, it is noteworthy that an international court acknowledged the relevance and evidential basis of the 2023 Synthesis Intergovernmental Panel on Climate Change (IPCC) Report. Thirdly, the Tribunal rejected the lex specialis argument, in respect of the Paris Agreement, illustrating that the Paris Agreement and UNCLOS entail separate obligations for States to fulfil independently. Fourthly, the Tribunal endorsed a synergistic approach to addressing climate change, incorporating obligations to reduce pollution from bunker fuels emitted by vessels and aircrafts throughout the opinion. For instance, States are obliged to reduce not only sea-based but also land-based pollution (para 441(e)). Fifthly, the Advisory Opinion embraced the due diligence principle within the United Nations Law of the Sea (UNCLOS) regime, aligning with the trend established in the Seabed Disputes Chambers (SDC), where States have a primary duty to enact domestic legislation to mitigate marine pollution from GHGs, through a common but differentiated responsibilities and respective capabilities (CBDRRC) lens.

II. Unlocking ITLOS Advisory Opinions: Exploring Jurisdictional Foundations

Advisory proceedings before the ITLOS are rare compared to the International Court of Justice (ICJ) and even the Inter-American Court of Human Rights (IACtHR), which have established advisory opinion procedures. Without an explicit jurisdiction (see here, here and here), ITLOS interpreted its authority to deliver advisory opinions through Article 21 of its Statute. The SRFC Advisory Opinion extended the jurisdictional basis to “all matters” stemming from other agreements, which would in this case be the COSIS Agreement (para 87). Thus, Article 21, together with “other agreements”, like the COSIS Agreement, enabled ITLOS to render an advisory opinion. This approach, supported by State Parties, is further endorsed by the recent BBNJ Agreement, which allows ITLOS to institute advisory proceedings per Article 47(7) BBNJ (see also here). This trend seems to further solidify and develop a technique of conferring an advisory jurisdictional basis to ITLOS through “other agreements” which expressly allow the Tribunal to answer advisory opinion requests.

Additionally, Article 138 of its Rules outlines three further preconditions for exercising advisory jurisdiction (paras 94-95). The Tribunal analysed questions (a) and (b) of the advisory request, concluding they involved legal issues requiring interpretation of UNCLOS and the COSIS Agreement, thus establishing jurisdiction (paras 102-104, 109).  Recognising climate change as a ‘common concern of humankind’ with significant impacts on the marine environment, the Tribunal decided to consider the request (para 122).

In terms of applicable law, the Tribunal chose not to follow the approach in the 2011 Advisory Opinion of the SDC of using both primary and secondary obligations. Instead, it focused on primary sources of international law, referring to secondary norms only if necessary (para 150). The Tribunal emphasised that relevant rules on anthropogenic GHG emissions are found not only in UNCLOS but also in other international instruments like the UNFCCC, the Kyoto Protocol, the Paris Agreement, Annex VI to MARPOL, Annex 16 to the Chicago Convention, the Montreal Protocol and its 2016 Kigali Amendment. This highlights the operation of systemic integration through Article 293 UNCLOS, requiring harmonious interpretation with external rules. Overall, the approach of ITLOS opening the gates of its advisory proceedings power, is innovative.

III. Combatting Marine Pollution: Prevention, Control, and Reduction

The Tribunal addressed the request for an advisory opinion in two parts, question (a) dealing with the actual prevention, control and reduction of pollution caused by anthropogenic GHG to the marine environment; and question (b) examining the specific obligations of States to preserve and protect the marine environment (para 139). The Tribunal’s answers to these questions are discussed in turn below.

a) GHG Emissions and Marine Pollution?

In relation to question (a) of the Advisory Opinion request, the Tribunal first analysed whether anthropogenic GHG emissions fall under the concept of “marine pollution” set out in UNCLOS (para 159). The Tribunal noted that there is no exhaustive list mentioned in UNCLOS that would prescribe what pollutants classify as marine pollution, as the Convention utilises a flexible three-tier criteria stemming from Article 1(1)(4) UNCLOS (para 161). Due to this flexible nature of the criteria, the Tribunal affirmatively answered that GHG emissions fall under Article 1(1)(4) UNCLOS (para 178). As such, this firmly establishes that GHGs are contributing to marine pollution.

i) State Obligations under Article 194 UNCLOS

The Tribunal addressed State Parties’ obligations under Article 194(1) UNCLOS to reduce, control, and prevent marine pollution through necessary measures (para 193). It emphasised the importance of scientific evidence, notably IPCC reports, in determining these measures (paras 208-212). However, in cases of scientific uncertainty, the precautionary principle should be applied (para 213).

The Tribunal highlighted the relevance of external treaties like Annex VI to MARPOL and Annex 16 to the Chicago Convention, which require control of pollution from vessels and aircrafts. This shows UNCLOS’s integration with sectoral international law regimes related to bunker fuels and GHG emissions.

The Tribunal clarified that measures under Article 194(1) UNCLOS are separate from and complementary to the Paris Agreement. Simply following the Paris Agreement’s mitigation measures is insufficient for addressing GHG emissions affecting the marine environment. Separate to the Paris Agreement, States must reduce marine pollution through UNCLOS and relevant international standards, or attract State responsibility under international law. The argument that the Paris Agreement is lex specialis was, therefore, rejected (paras 222-224).

The obligation to reduce, control, and prevent marine pollution is based on due diligence, a principle that ITLOS and the SDC applied even to deep seabed mining, finding that Sponsoring States must establish domestic legislative frameworks (paras 229, 233, 239). Citing the 2023 IPCC Synthesis Report, the Tribunal emphasised the imminent threat of climate change to the marine environment, concluding that a “stringent” standard is necessary (para 241). However, this standard will vary among States, in line with the CBDRRC principle, meaning richer States must do more than developing and more vulnerable States with fewer capabilities (para 441(c)).

Regarding Article 194(2) UNCLOS, the Tribunal noted that States must ensure activities within their jurisdiction do not cause pollution damage to other States or the environment (para 245). This includes preventing pollution incidents from spreading beyond areas of their sovereign rights. The Tribunal applied the due diligence standard from the SDC to prevent transboundary harm, indicating that this obligation is even more stringent than under Article 194(1) UNCLOS due to its focus on transboundary prevention. This is apt evidence that the due diligence principle is the centrepiece of effectively reducing, controlling and preventing marine pollution from GHGs.

ii) Synergistic Approach

The Tribunal concluded its response to the first question on the obligation of States to prevent, control, and reduce pollution from GHGs by establishing specific obligations of States regarding pollution sources, focusing particularly on Articles 207 to 212 UNCLOS (paras 259-264). The Tribunal highlighted three primary sources of marine pollution: land-based pollution, vessels, and aircrafts.

For land-based pollution, the Tribunal stated that States have a duty to participate in climate change regimes, such as the Paris Agreement via Article 207(4), and implement national legislation to reduce GHGs (paras 266-273). As such, it found that States must continually endeavour to strengthen the entire climate change regime through various global or regional legal instruments. For aircrafts, under Article 212 UNCLOS, States are required to enact national laws to reduce atmospheric pollution and follow international standards, including Volume IV of Annex 16 to the Chicago Convention, which established the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA). Similar due diligence duties apply to States in relation to pollution emitted by vessels by implementing International Maritime Organisation (IMO) standards and rules (para 277).

The Tribunal’s approach integrates the climate change regime under the UNFCCC and its protocols with GHG emissions from shipping and aviation sectors, which the Kyoto Protocol “arguably” delegated to the IMO and the International Civil Aviation Organisation (ICAO) under Article 2(2) (see here, here and here). This synergistic method connects sectoral approaches to bunker emissions with broader climate change targets, moving away from a fragmented approach to a cohesive international climate change regime consistent not only of one legal instrument. This approach is highly appreciated.

b) More Adaptation and Corporate Accountability is Needed!

In addressing question (b) regarding States’ obligations to protect and preserve the marine environment in relation to climate change, the Tribunal first emphasised the broad scope of Article 192 UNCLOS in safeguarding and conserving the marine environment (para 385). A notable aspect developed by the Tribunal is the obligation on States to restore degraded areas of the marine environment affected by pollution through the ecosystem approach (para 386). This underscores the importance of not only mitigating, preventing, controlling, and reducing marine pollution from GHGs but also implementing adaptation measures, which are often deemed inadequate and slow under the UNFCCC regime, according to Leiter. Given the ocean’s significant role as a blue carbon sink, States must address both GHG emissions affecting the marine environment and implement measures to adapt to adverse climate change impacts (para 392-393). A significant advancement forward, is the development of the obligation of States to ensure that non-State actors, such as corporations and carbon majors, comply with preservation and protection measures under their jurisdiction (para 396). This provision marks progress in corporate accountability, requiring States to take due diligence actions, potentially even against fossil fuel companies and subsidies.

IV. Looking Forward

Looking ahead, there is hope that the ICJ will adopt a similarly synergistic approach in its forthcoming advisory opinion. States are currently preparing their written submissions, due by June 24, 2024. It is anticipated that the ICJ will address one or more of the key features mentioned earlier, potentially fostering additional synergies between various international legal instruments to further advance efforts in combating climate change.

Renatus Otto Franz Derler LLB (Buckingham), LLM (Cantab), and MPhil in Environmental Policy Candidate at the University of Cambridge. He is also a Researcher at the Centre for International Sustainable Development Law, and Blog Manager and Managing Editor (2023-24) with the Cambridge International Law Journal.

The author would like to thank Professor Harro van Asselt and Richard Wagenlander, BA (Oxon), LLM (Cantab), for their invaluable comments. Any remaining mistakes are my own.