Summary
On May 21st, the International Tribunal for the Law of the Sea (ITLOS) issued a landmark, unanimous Advisory Opinion on climate change, in response to a request from the (COSIS).
The Tribunal concluded that the United Nations Convention on the Law of the Sea (UNCLOS) obliges its 169 States Parties to implement specific, concrete measures to prevent, reduce, and control marine pollution caused by greenhouse gas emissions.
This ruling marks the first time where an international court has explicitly ruled on countries’ international legal obligations to mitigate climate change within the framework of the 1982 United Nations Convention on the Law of the Sea (UNCLOS).
To read the full case note in Portuguese, click here.
Case Note: ITLOS Advisory Opinion on Climate Change
Case Background: The Impact of Climate Change on Small Island States
Small island states face an existential threat from climate change, experiencing its effects more intensely and urgently than many other regions. The ocean’s absorption of 90% of excess heat from greenhouse gases leads to gradual ocean acidification and warming, resulting in sea level rise that endangers these nations by potentially submerging low-lying areas, intensifying coastal erosion, and causing land loss.
Without adequate adaptation measures, projections suggest certain island states could be completely submerged by the century’s end due to current warming trends. Moreover, sea level rise risks contaminating freshwater aquifers with saltwater, compromising access to clean drinking water and irrigation for island inhabitants, thereby jeopardizing food security and public health, and potentially rendering these states uninhabitable.
The warming and acidification of the oceans profoundly affect marine life critical to the biodiversity and economy of these states, with coral reefs being vulnerable. The loss of coral reefs weakens the protective barrier against waves and jeopardizes tourism and fishing industries. Additionally, climate change leads to extreme weather events such as tropical cyclones, causing havoc on infrastructure and displacing populations.¹ Thus, small island states are on the front line of climate change and urgently seek redress and protection under international law.
The Request by COSIS
The Commission of Small Island States on Climate Change and International Law (COSIS) is an intergovernmental organization comprising small island states from the Caribbean and the Pacific. It was formed in October 2021 by Antigua and Barbuda and Tuvalu as original signatories, coinciding with the COP26 United Nations climate negotiations in Glasgow.
COSIS aims to promote and contribute to the definition, implementation, and progressive development of rules and principles of international law concerning climate change, including the obligations of states relating to the protection and preservation of the marine environment and their responsibility for injuries arising from internationally wrongful acts regarding such obligations.²
On December 12, 2022, COSIS requested an advisory opinion from the International Tribunal for the Law of the Sea (ITLOS) concerning State Parties’ obligations under the 1982 United Nations Convention on the Law of the Sea (UNCLOS), which provides the legal framework governing ocean space and maritime activities.
In its request, COSIS sought clarification on state parties’ obligations regarding the prevention, reduction, and control of marine pollution due to climate change effects, such as ocean warming, sea level rise and ocean acidification caused by human-generated greenhouse gas (GHG) emissions.
Additionally, they sought clarifications on state parties’ obligations concerning the protection and preservation of the marine environment in response to climate change impacts, including ocean warming, sea level rise and ocean acidification.
Throughout the process, 32 states, the European Union, and nine intergovernmental organizations, including COSIS, the African Union and the International Union for the Conservation of Nature, submitted contentions concerning states’ obligations under UNCLOS in light of the climate crisis.
ITLOS Advisory Opinion
On May 21, 2024, the Tribunal issued a landmark Advisory Opinion determining that GHG emissions constitute marine pollution according to UNCLOS, and consequent to this finding, states are obliged to undertake all necessary measures to reduce their GHG emissions to the maximum feasible extent, aligning with UNCLOS and other pertinent international legal obligations.
This Case Note wish to highlight three key findings of the Advisory Opinion regarding the meaning of pollution of marine environment, the obligation to implement all necessary measures and the duty to exercise due diligence.
The meaning of marine pollution
Since UNCLOS does not explicitly designate GHG emissions as a distinct pollutant, nor does it explicitly reference climate change and ocean acidification, the Tribunal faced the preliminary task of determining whether GHG emissions fall within UNCLOS’s definition under Article 1(1)(4) of “pollution of the marine environment.”
To do so, the Tribunal had to assess whether the three cumulative criteria determining such pollution are met; 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.
Following its analysis, the Tribunal concluded that human-generated GHG emissions released into the atmosphere—whether from vessels or aircraft, land-based sources or ocean-based activities—constitute pollution of the marine environment under the Convention’s provisions [159-179].
This determination was pivotal in establishing the obligations imposed on states regarding marine pollution, as will be discussed next.
The obligation to take all necessary measures
Article 194(1) of UNCLOS imposes upon states the obligation to implement individually or jointly, as appropriate, all necessary measures to prevent, reduce and control pollution of the marine environment from any source, using for this purpose the best practicable means at their disposal and in accordance with their capabilities. The Tribunal underscored that necessary measures encompass not only actions essential for the prevention, reduction and control of marine pollution, but also other interventions facilitating the achievement of this objective [203].
In the context of addressing climate change impacts, these interventions are commonly referred to as “mitigation measures”, and at their core lies the reduction of anthropogenic GHG emissions into the atmosphere [205]. The Tribunal highlighted that defining these measures does not mean accepting any measures states deem necessary to that end. Instead, the measures necessary should be grounded in an objective evaluation, taking into consideration relevant factor [206-207], including:
The best available scientific evidence, notably publications by the Intergovernmental Panel on Climate Change (IPCC), which the Tribunal acknowledged as reflecting ´´scientific consensus´´ [208]. When scientific certainty is lacking, ITLOS emphasised the importance of applying the precautionary and ecosystem-based approach, underscoring the heightened necessity of this approach for marine pollution resulting from anthropogenic GHG emissions, given the serious and irreversible damage that may be caused to the marine environment by such pollution [213].
International rules and standards, such as those outlined in the United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Agreement, which serve as crucial benchmarks for guiding these measures. Of particular significance is the global temperature target of limiting the temperature increase to 1.5°C above pre-industrial levels, as established in the Paris Agreement, along with the emission pathways necessary to achieve this objective. However, the Tribunal stressed that simply adhering to the obligations and commitments outlined in the Paris Agreement would not be adequate to fulfil the obligations under UNCLOS. While both agreements aim to tackle environmental concerns, they are distinct treaties with different sets of obligations. Therefore, ITLOS underscored that safeguarding the marine environment, a core objective of UNCLOS, requires compliance with its obligations regardless of those delineated in the Paris Agreement [222-223].
Best available means and capabilities, when exercising their obligation under Article 194 of UNCLOS to take all necessary measures to address marine pollution stemming from anthropogenic GHG emissions. Such flexibility acknowledges the varying resources and capabilities among states and aims to ease the burden on those with limited means. However, the Tribunal stressed that this flexibility should not be used as an excuse to delay or exempt from taking necessary measures [225-226]. The Tribunal clarified that states with greater means and capabilities are expected to ´´take the lead´´ and undertake more substantial efforts compared to those with fewer resources, recognizing the principle of common but differentiated responsibilities and respective capabilities, in line with the UNFCCC and the Paris Agreement. However, the Tribunal underscored that although measures to reduce anthropogenic GHG emissions causing marine pollution may vary between developed and developing states, all states are mandated to undertake mitigation efforts, irrespective of their developmental status [227-229] [338-339].
The obligation to exercise due diligence
When reaffirming that states are obligated to take all necessary measures to prevent, reduce, and control marine pollution, the Tribunal clarified that such obligation is one of conduct, requiring states to exert their best efforts to achieve the intended result, rather than guaranteeing the prevention, reduction, and control of marine pollution at all times [233].
According to the Tribunal, the obligation of due diligence, integral to this requirement, mandates states to establish a national system, including legislation, administrative procedures, and an enforcement mechanism necessary to regulate the activities contributing to marine pollution, and to exercise adequate vigilance to ensure the effective functioning of such a system, with the aim of achieving the intended objective of mitigating climate change impacts [232-238].
In this regard, the Tribunal further clarified that the standard of due diligence varies depending on factors such as scientific knowledge, international rules and standards and the level of risk and urgency involved [239]. Particularly in the context of marine pollution from anthropogenic GHG emissions, the Tribunal emphasized that the standard of due diligence must be stringent due to the high risk and severity of harm to the marine environment. Thus, all states must implement measures within their capabilities [241].
Finally, the Tribunal highlighted the close link between the obligation of due diligence and the precautionary approach, requiring states to consider and mitigate risks even in the absence of complete scientific certainty [242].
The significance of the Advisory Opinion
The ITLOS advisory opinion marks a significant step forward in integrating international maritime law with global climate governance. It outlines, for the first time, states’ obligations under UNCLOS to combat pollution of the marine environment from GHG emissions and mitigate climate change impacts. Serving as a vital reference, it enlightens policymakers on these obligations, shaping future climate negotiations.
Moreover, the opinion offers clear legal directives for courts, facilitating the interpretation of state duties and the adjudication of climate-related cases, especially related to small island states. By clarifying climate impacts and responsibilities, it establishes a precedent for future cases and underscores the necessity for environmental diligence and emission reduction policies.
The opinion underscores UNCLOS’s pivotal role in addressing climate challenges and advancing global environmental preservation. Thus, it emphasizes the need to assess states’ actions also according to UNCLOS guidelines and serves as warning of international accountability if UNCLOS obligations are ignored, urging major emitters to act proactively.
Footnotes:
- IPCC, 2023: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, 184 pp., doi: 10.59327/IPCC/AR6-9789291691647. OHCHR Press Release, Small Island Developing States summit: UN experts urge States and development banks to support endangered islands, 23 May 2024.
- Agreement for the establishment of the Commission of Small Island States on Climate Change and International Law. Edinburgh, 31 October 2021, Article 1 (3).
Author: Natalie Rosen
