The International Tribunal for the Law of the Sea (ITLOS) delivered an advisory opinion clarifying the specific obligations of States under the UN Convention on the Law of the Sea (UNCLOS) with respect to climate change.

On 12 December 2022, the Commission of Small Island States on Climate Change and International Law (COSIS) requested the Tribunal to issue an advisory opinion on the following questions:

What are the specific obligations of UNCLOS State Parties, including under Part XII:

• To prevent, reduce, and control pollution of the marine environment in relation to the deleterious effects that result or are likely to result from climate change, including through ocean warming and sea level rise, and ocean acidification, which are caused by anthropogenic greenhouse gas (GHG) emissions into the atmosphere?
• To protect and preserve the marine environment in relation to climate change impacts, including ocean warming and sea level rise, and ocean acidification?

On 21 May 2024, ITLOS delivered a 153-page unanimous ruling, responding to the questions posed by COSIS.

With respect to the first question, the Tribunal finds that anthropogenic GHG emissions into the atmosphere constitute pollution of the marine environment. It further finds that under UNCLOS, countries “have the specific obligations to take all necessary measures to prevent, reduce and control marine pollution from anthropogenic GHG emissions and to endeavour to harmonize their policies in this connection,” based on the best available science and relevant international rules and standards, including the UNFCCC and the Paris Agreement on climate change. While the scope and content of such measures may vary depending on countries’ capabilities, ITLOS finds they should be determined taking into account the Paris Agreement’s 1.5°C temperature goal.

The Tribunal finds that the obligation to take all necessary measures to prevent, reduce, and control marine pollution from anthropogenic GHG emissions is an obligation of due diligence and that given the risks of serious and irreversible harm to the marine environment, the due diligence standard is “stringent.”

According to the advisory opinion, States do not only have the obligation to take all necessary measures to prevent, reduce, and control marine pollution from anthropogenic GHG emissions with respect to areas under their jurisdiction or control, but also in a transboundary setting.

In terms of sources, the Tribunal distinguishes three categories of marine pollution from anthropogenic GHG emissions: pollution from land-based sources; pollution from vessels; and pollution through the atmosphere. It finds that States have the specific obligations to adopt laws and regulations to prevent, reduce, and control marine pollution from GHG emissions with respect to all three sources.

In addition, ITLOS finds States have the specific obligations to, inter alia:

• Cooperate, directly or through competent international organizations, to prevent, reduce, and control marine pollution from anthropogenic GHG emissions, including on: formulating and elaborating rules, standards, and recommended practices; promoting studies, undertaking scientific research, and encouraging the exchange of information and data; and establishing appropriate scientific criteria for rules and standards;
• Assist developing States, in particular vulnerable developing States, in their efforts to address marine pollution from anthropogenic GHG emissions, including through technical, technological, financial, and capacity-building assistance; and
• Monitor and publish reports of the activities they permit, and conduct environmental impact assessments (EIAs) as a means to address marine pollution from anthropogenic GHG emissions.

With respect to the second question, the Tribunal finds that the obligation under UNCLOS to protect and preserve the marine environment is broad in scope, “encompassing any type of harm or threat to the marine environment.” Therefore, according to the advisory opinion, States “have the specific obligation to protect and preserve the marine environment from climate change impacts and ocean acidification,” including restoring marine habitats and ecosystems where the marine environment has been degraded.

ITLOS describes this obligation as one of due diligence, accompanied by a stringent standard due to “the high risks of serious and irreversible harm to the marine environment from climate change impacts and ocean acidification.”

Per the advisory opinion, the specific obligations of States also extend to, inter alia:

• Protecting and preserving rare or fragile ecosystems;
• Taking measures necessary to conserve the living marine resources threatened by climate change impacts and ocean acidification;
• Cooperating with a view to adopting effective measures necessary to coordinate and ensure the conservation and development of shared stocks; and
• Taking appropriate measures to prevent, reduce, and control pollution from the introduction of non-indigenous species due to the effects of climate change and ocean acidification.

In the context of preventing, reducing, and controlling pollution of the marine environment, “specific obligations” refer to “concrete or particularized obligations, in contrast to general obligations.” “It may also mean obligations specific to pollution of the marine environment in relation to the deleterious effects arising from climate change and ocean acidification,” according to the advisory opinion. The Tribunal considered both aspects of the term “specific” in responding to the two questions before it.

Several other proceedings seeking to clarify responsibilities of States in relation to climate change are ongoing, including the high-profile request for an advisory opinion from the International Court of Justice (ICJ). The ICJ is expected to deliver its ruling later this year. [Publication: Request for an Advisory Opinion Submitted by the Commission of Small Island States on Climate Change and International Law: Advisory Opinion] [ITLOS Press Release] [Request for an Advisory Opinion]

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This story is part of a project that seeks to raise awareness and build momentum and knowledge around the ICJ advisory opinion on obligations of States in respect of climate change and to promote a better understanding of the implications of the advisory opinion among sustainable development decision makers.