Advocacy update

ITLOS Advisory Opinion on Climate Harm and the Marine Environment: a Summary

May 21, 2024
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On May 21, 2024, the International Tribunal for the Law of the Sea (ITLOS) delivered the first international judicial opinion on state obligations concerning climate change. ITLOS’s much-anticipated advisory opinion clarifies the obligations of states under international law to protect the marine environment from the adverse effects of climate change. It found unanimously that greenhouse gas emissions (GHG) constitute pollution of the marine environment and that States are under an obligation to take all necessary measures to control pollution from GHG emissions. The Tribunal also found that States are under special obligations to protect and preserve the marine environment in relation to climate change impacts. This authoritative legal opinion will fortify international climate commitments and compel stronger actions to mitigate climate harm.  


Applicability of Convention Obligations to Climate Change 

1. Anthropogenic Greenhouse Gases Constitute Marine Pollution 

The Tribunal unanimously concludes that GHG emissions constitute pollution of the marine environment within the meaning of Article 1(1)(4) of UNCLOS. This article defines pollution as the introduction by humans, directly or indirectly, of substances or energy into the marine environment that results in ocean warming, sea level rise, acidification, and deoxygenation that causes harmful effects such as hazards to marine life, human health, hindrance to marine activities, impairment of water quality, and reduction of amenities. 

2. State Obligations Under Article 194(1) of UNCLOS 

Article 194(1) of UNCLOS requires states to take all necessary measures to prevent, reduce, and control pollution of the marine environment from any source, including GHG emissions. The Tribunal emphasizes that this obligation does not mandate the immediate cessation of pollution from GHG emissions. Instead, states must take all practicable measures individually or jointly, as appropriate. This includes the obligation to adopt mitigation measures, including to reduce GHG emissions into the atmosphere. Such measures should be based on the best available science. 

Application of the Precautionary Approach: In determining the necessary measures, the Tribunal clarifies that scientific certainty is not required. States must apply the precautionary approach, which mandates proactive measures to prevent environmental harm even in the face of scientific uncertainty. The damage that may be caused to the marine environment by GHG emissions must be assessed based on the best available science.  

Relevance of UNFCCC and Paris Agreement: The Tribunal acknowledges that the UNFCCC and the Paris Agreement are the primary legal instruments addressing climate change and are relevant to the interpretation and application of UNCLOS. ITLOS clarified that State obligations are not limited to the commitments in the Paris Agreement since it does not override or modify the obligations under Article 194(1) of UNCLOS. 

Due Diligence Obligation: Obligations under Article 194(1) require states to act with due diligence. This entails taking all necessary and appropriate measures to prevent, reduce, and control marine pollution. States must apply the precautionary approach in their exercise of due diligence, ensuring that their actions are effective in mitigating climate-related harms. ITLOS explained, “The standard of due diligence is stringent, given the high risks of serious and irreversible harm to the marine environment from such emissions.” 

Due Diligence extends to Non-State Actors: States must ensure that non-state actors under their jurisdiction and control comply with the obligation to protect and preserve the marine environment. This obligation is one of due diligence, requiring states to exercise appropriate oversight and enforcement to prevent harm from non-state activities. If a State has acted with due diligence in relation to private actors, ITLOS noted that it would not be reasonable to hold a State accountable for pollution occurring from the activities of private actors. Conversely, therefore, a State which has failed to exercise due diligence, because it did not put in place a system to regulate the activities of private actors may be held accountable for the resulting pollution.  

2. State Obligations Under Article 194(2) of UNCLOS 

States are under a particular obligation in relation to transboundary pollution under Article 194(2). States have to take all necessary measures to ensure that activities under their jurisdiction do not cause damage by pollution to other States and their environment and that pollution arising from their activities does not spread beyond the limits of their national jurisdiction.  

Due Diligence Obligation: The Tribunal emphasised that the obligation in relation to transboundary pollution under Article 194(2) is also an obligation of due diligence. Because of the nature of transboundary pollution, ITLOS emphasised that the standard of due diligence under Article 194(2) may be more stringent than the due diligence standard under Article 194(1). The Tribunal considered that the questions concerning whether a State’s emissions were causing harm to a remote state were distinguishable from the application of the obligations under Article 194(2) to marine pollution from anthropogenic GHG. 

3. Duty to Cooperate 

The Tribunal finds that Articles 197, 200, 201, 194, and 192 impose specific obligations on states to cooperate. States must work together directly or through competent international organizations continuously, meaningfully, and in good faith to control pollution from GHG emissions. This cooperative duty is crucial for addressing the transboundary nature of climate change impacts. 

Special Obligations to Protect and Preserve the Marine Environment 

The second question that had been asked to ITLOS was on whether States have special obligations to protect and preserve the marine environment in relation to climate change impacts and ocean acidification. 

1. Obligation Under Article 192 

Article 192 of UNCLOS imposes a general obligation on states to protect and preserve the marine environment. This includes preventing or mitigating environmental harm and, where degradation has occurred, restoring the environment. The Tribunal reiterates the obligation to take mitigation measures as discussed in response to Question A. 

2. Obligation under Article 194(5) 

Article 194(5) imposes a specific duty to the general obligation of Article 192 to adopt measures necessary to protect rare or fragile ecosystems as well as the habitat of depleted, threatened or endangered species and other forms of marine life from climate change impacts. As noted by ITLOS, these rare or fragile ecosystems may be particularly threatened by glowing warning and acidification. The Tribunal noted that this may call for specific measures, including enacting and enforcing laws and regulations and monitoring and assessing these ecosystems.  

3. Obligations under other provisions of the Convention 

Conservation and Management of Living Resources: Under Articles 119 and 61 of UNCLOS, states must adopt objectively reasonable approaches to the conservation and management of living resources on the high seas. This includes applying the precautionary approach and the ecosystem approach to account for the impacts of climate change and ocean acidification on marine biodiversity. 

Obligations to Seek Agreement and Cooperate: Articles 63(1) and 64(1) of UNCLOS require states to consult in good faith with a view to adopting effective measures necessary for the conservation and development of shared stocks. This cooperation must consider the impacts of climate change and ocean acidification. Additionally, Article 118 imposes a specific obligation on states to cooperate in conserving living marine resources in the high seas threatened by climate change impacts. 

Prevention of Non-Indigenous Species Introduction: Article 196 of UNCLOS obliges states to take appropriate measures to prevent, reduce, and control pollution from the introduction of non-indigenous species due to climate change and ocean acidification. This requires the application of the precautionary approach to mitigate the significant and harmful changes these species can cause to the marine environment. 


What is ITLOS? 

ITLOS is an international court established under the United Nations Convention on the Law of the Sea (UNCLOS). Based in Hamburg, Germany, ITLOS adjudicates disputes arising out of the interpretation and application of UNCLOS. The tribunal has jurisdiction over a wide range of maritime issues, including the protection and preservation of the marine environment. It has the discretionary authority to issue advisory opinions in response to requests from international organizations. 

What is COSIS? 

The Commission of Small Island States on Climate Change and International Law (COSIS) is an international organization established by a coalition of countries highly vulnerable to the impacts of climate change. Formed in 2021 by Antigua and Barbuda and Tuvalu, COSIS aims to define and enforce state obligations under international law to safeguard the marine environment. COSIS member states now include Antigua and Barbuda, Tuvalu, Palau, Niue, Vanuatu, Saint Lucia, Saint Vincent and the Grenadines, Saint Kitts and Nevis, and the Bahamas. 


In December 2022, COSIS submitted a legal request to ITLOS seeking an advisory opinion on the scope of state obligations under UNCLOS to protect the marine environment from climate harms. This request specifically asks whether states’ failure to limit greenhouse gas emissions, which negatively affect the marine environment, constitutes a breach of UNCLOS, and whether states must take steps to mitigate such harm. 

The request focuses on the obligations of States Parties under the United Nations Convention on the Law of the Sea (UNCLOS) to address marine pollution and protect the marine environment from the impacts of climate change. Thirty-four states and nine international organizations filed submissions to ITLOS and were part of the proceedings. 


The Open Society Justice Initiative supported submissions of the Republic of Mozambique and Republic of Sierra Leone, working with Professor Phoebe Okowa, Professor Charles Jalloh, Professor Dire Tladi, and Foley Hoag LLP partners Christina Hioureas and Andrew Loewenstein, as well as climate scientists from the Union of Concerned Scientists.  

The submissions argued that the Convention must be interpreted and applied to give effect to the best scientific evidence, which conclusively establishes that greenhouse gas emissions are causing devastating harm to the world’s oceans. States are thus legally required, as an absolute minimum, to take all necessary measures, individually and collectively, to limit the increase in global average temperatures to 1.5˚C above pre-industrial levels. 



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