Advisory Opinion on Climate Change and the Law of the Sea

The International Tribunal for the Law of the Sea (“ITLOS” or “Tribunal”) is a judicial body that was established by the 1982 U.N. Convention on the Law of the Sea (“UNCLOS” or “Law of the Sea”). The Tribunal settles disputes over the interpretation or application of the Law of the Sea.

In 2022, the Commission of Small Island States on Climate Change and International Law sent a letter to ITLOS asking the Tribunal to issue an advisory opinion on climate change. Specifically, the Commission asked ITLOS to clarify state obligations to:

1. prevent pollution of the marine environment in relation to greenhouse gas (GHG) emissions, which are causing climate change; and,
2. “protect and preserve the marine environment in relation to climate change impacts, including ocean warming and sea level rise, and ocean acidification” (Request for an Advisory Opinion, p. 2)

The Tribunal subsequently took up the request and invited parties to weigh in on the Commission’s questions. Dozens of countries and interested organizations submitted written statements and provided oral testimony to the Tribunal.

ITLOS: Emissions Pollute the Marine Environment

In May 2024, ITLOS became the first international judicial body to issue an opinion on climate change. The unanimous opinion stated, in no uncertain terms, that states have an obligation, under the U.N. Convention on the Law of the Sea (UNCLOS or “Law of the Sea”), to protect and preserve the world’s oceans from climate change.

Through careful textual and scientific analysis, the Tribunal first determined that GHG emissions into the atmosphere constitute “pollution of the marine environment” under UNCLOS Article 1(1)(4). GHGs are directly absorbed by the oceans and they trap heat within the atmosphere, which the ocean then stores (Advisory Opinion, ¶172).  The introduction of CO2 and heat has a variety of negative impacts on the oceans, such that they can be considered pollutants (¶172). As a result, GHG emissions into the atmosphere cause pollution of the marine environment by introducing carbon and energy to the oceans. This broad, but carefully reasoned, interpretation of the Law of the Sea laid a foundation for the Tribunal’s sweeping advisory opinion on climate change.

States Must Reduce Emissions

In multiple provisions, the Law of the Sea requires states to “prevent, reduce and control marine pollution” and take steps to protect and preserve “rare or fragile ecosystems” and the habitat of “depleted, threatened, or endangered” marine life (¶195).

ITLOS explained that states have an obligation to take “all necessary measures” to reduce and control GHG emissions, however this does not “entail the immediate cessation of marine pollution from anthropogenic GHG emissions” (¶199). Some states, particularly those in the Global South, may not be able to rapidly eliminate their GHG emissions. The Tribunal explained that states should take action individually or jointly, and that states cannot meet their obligations “exclusively through participation in the global efforts to address . . . climate change” (¶202). In this way, the Tribunal rejected the argument advanced by some countries that only joint, international action can prevent climate change.

Notably, the Tribunal clarified that state action must be evaluated by an objective metric. While states are free to determine how they will prevent, reduce, and control GHG emissions, this does not mean that they can meet their legal obligations through whatever measures they deem necessary (¶206). Rather, the best available science, state capabilities, and international standards (such as those in the Paris Agreement), among other considerations, will determine what state action is necessary (¶¶207, 214). ITLOS further specified that “the best available science is found in the works of the IPCC,” however, “scientific certainty is not required . . . [as] States must apply the precautionary approach” in regulating GHG emissions (¶¶208, 213). This means that complying with the Paris Agreement will not, on its own, be sufficient to satisfy a country’s obligations under the Law of the Sea.

To satisfy its obligations, a state must act with due diligence to reduce GHG emissions. This must be a “stringent” standard, given the severe risk posed by climate change (¶241). Indeed, “States must apply the precautionary approach in their exercise of due diligence” (¶242).

The Tribunal also noted the differentiated responsibilities of states. It explained that “States with greater means and capabilities must do more to reduce such emissions than States with less means and capabilities” (¶227). However, this should “not be used as an excuse to unduly postpone,” or avoid taking, steps to reduce GHG emissions, as “[a]ll states must make mitigation efforts” (¶¶226, 229). Additionally, the Law of the Sea sets out an obligation to assist developing states, particularly climate-vulnerable states, with their efforts to address GHG pollution (¶339). This could include scientific, technical, or educational assistance.

ITLOS also elaborated on several specific state obligations related to mitigation efforts. Under the Law of the Sea, states must attempt to establish global and regional rules, standards, and practices to regulate GHG emissions (¶273). Similarly, states have a duty to cooperate on creating a joint regulatory framework, conducting scientific research, and exchanging such research (¶¶301-321). They also must regulate emissions from ships “flying their flag or of their registry,” adopt laws and regulations to limit GHG pollution, and enforce these laws and regulations. (¶¶279, 284-285). Lastly, states are obligated to “monitor the risks or effects of pollution, to publish reports and to conduct environmental impact assessments” (¶367).

States Must Protect the Marine Environment

In response to the Commission’s second question, ITLOS recognized that states have a general obligation to combat degradation of the marine environment caused by climate change. This obligation extends beyond the obligation to prevent and reduce GHG pollution, requiring states to take action even after this pollution has occurred.

The Tribunal explained that “[w]here the marine environment has been degraded, this may require restoring marine habitats and ecosystems” (¶400). In other words, states must help the marine environment adapt to climate change and repair climate-induced damage to the marine environment, in addition to mitigating GHG emissions. This includes a specific obligation to “to protect and preserve 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 and ocean acidification” (¶406). The Tribunal also observed that marine protected areas may be an effective strategy for protecting the oceans from climate change impacts (¶438).

To effectively conserve marine life, states will need to consider the economic and cultural impact of climate change on coastal communities.  Climate change and ocean acidification affect fish distribution and reduce fish populations, which may put pressure on the income, livelihoods, and cultural practices in communities that depend on marine life (¶410).

Articulating an obligation to cooperate internationally

The ITLOS Advisory Opinion is notable for its clear articulation of an obligation to cooperate internationally. The Tribunal held:

[The Law of the Sea] impose[s] specific obligations on States Parties to cooperate, directly or through competent international organizations, continuously, meaningfully and in good faith in order to prevent, reduce and control marine pollution from anthropogenic GHG emissions . . . [they] are required to cooperate in formulating and elaborating rules, standards and recommended practices and procedures, consistent with the Convention and based on available scientific knowledge, to counter marine pollution from such emissions . . . [and they] are required to cooperate to promote studies, undertake scientific research, and encourage the exchange of information and data on marine pollution from anthropogenic GHG emissions, its pathways, risks and remedies, including mitigation and adaptation measures . . .

(¶321)

ITLOS further specified that this is a continuing set of obligations, such that the adoption of a particular treaty “does not discharge a State from its obligation to cooperate” (¶311).

Additionally, states have an obligation to cooperate on conserving marine life, promoting studies, undertaking scientific research, and encouraging the exchange of information and data on marine pollution from GHG emissions and potential responses (¶441(3)(j)).

In total, this represents one of the most comprehensive and authoritative judicial commands to cooperate on climate change.

Tying countries’ / corporations’ climate and human rights obligations to international climate and environmental law, including, for example, the temperature target established by the Paris Agreement

ITLOS explained that state obligations under the Law of the Sea should be informed by standards set by international climate law, such as the UNFCCC and the Paris Agreement. In particular, the obligation to mitigate GHG emissions should be assessed according to the global temperature goal set out in the Paris Agreement (¶441(3)(b)). This gives added force to the Paris Agreement, since it establishes a binding legal obligation to act with due diligence in mitigating GHG emissions at a pace that aligns with the Paris Agreement goals. The Paris Agreement itself does not bind states to any level of ambition.  

The Law of the Sea may prove to be a valuable tool in climate litigation. The Advisory Opinion establishes the Law of the Sea as an instrument of climate law. The opinion sets out a comprehensive set of legal obligations that interlock with and reinforce other instruments of climate law, such as the UNFCCC and the Paris Agreement. This decision applies to 169 parties to the convention. As a result, the Law of the Sea now serves as an additional legal basis for government action to reduce GHG emissions. Litigants demanding government action on climate change will be able to cite state obligations under the Law of the Sea. For many states, this Advisory Opinion establishes the first legal obligation to take action on climate change, since many jurisdictions have not recognized a legal obligation to reduce GHG emissions. The Advisory Opinion changes this. In doing so, the opinion gives advocates a new tool for legal action.

The Law of the Sea requires environmental impact assessments that take GHG emissions into account. One key element of the opinion is the Tribunal’s recognition of a legal requirement to conduct an environmental impact assessment (EIA) that includes consideration of GHG emissions. ITLOS explained:

Any planned activity, either public or private, which may cause substantial pollution to the marine environment or significant and harmful changes thereto through anthropogenic GHG emissions, including cumulative effects, shall be subjected to an environmental impact assessment. Such assessment shall be conducted by the State Party under whose jurisdiction or control the planned activity will be undertaken with a view to mitigating and adapting to the adverse effects of those emissions on the marine environment. The result of such assessment shall be reported [publicly].

(¶367)

ITLOS further indicated:

[EIAs may consider] not only the specific effects of the planned activities concerned but also the cumulative impacts of these and other activities on the environment . . . In the context of pollution of the marine environment from anthropogenic GHG emissions, planned activities may not be environmentally significant if taken in isolation, whereas they may produce significant effects if evaluated in interaction with other activities.

(¶365)

These passages provide key guidance for EIA assessments and serve as valuable precedent for legal proceedings around the world. Many climate change cases have involved challenges to EIAs that failed to consider GHG emissions and their downstream, systemic impacts. Communities challenging such EIAs can now cite the ITLOS Advisory Opinion.

The Law of the Sea provides a stringent due diligence standard for evaluating government action on climate change. The Advisory Opinion spent considerable effort establishing that states have a stringent duty of due diligence to take action on climate change. This duty serves as a metric for evaluating whether states have, on an objective level, taken steps to reduce GHG emissions and protect the marine environment.

The duty of due diligence helps to fill a conceptual gap in climate law: the general absence of a standard for assessing government action on climate change. Governments often argue that they are taking sufficient action on climate change, or that the standard for evaluating their climate action is fundamentally a political question (and therefore non-justiciable). The duty of due diligence, assessed according to the best available science and the temperature goals set out in the Paris Agreement, offers a fairly concrete answer to whether a state is taking sufficient action. And courts often apply due diligence standards in other legal contexts, such that it is clearly a justiciable question. In other words, a court can clearly and fairly assess whether or not a government has made a reasonable effort to reduce GHG emissions at a pace that would allow the world to stay well below 2° C of warming.

The Tribunal explained that the standard of due diligence is stringent in the context of climate change, given the serious risk posed by falling short. This standard will not be merely met by a vague set of ‘best efforts;’ due diligence requires concrete legislation and enforcement. Additionally, due diligence requires states to apply the precautionary principle and err on the side of disallowing GHG pollution (¶242).