Historic Advisory Opinion Issued By The International Tribunal For The Law Of The Sea On States' International Obligations Regarding Oceans And Climate Change

Miller Thomson LLP


Miller Thomson LLP (“Miller Thomson”) is a national business law firm with approximately 525 lawyers working from 10 offices across Canada. The firm offers a complete range of business law and advocacy services. Miller Thomson works regularly with in-house legal departments and external counsel worldwide to facilitate cross-border and multinational transactions and business needs. Miller Thomson offices are located in Vancouver, Calgary, Edmonton, Regina, Saskatoon, London, Waterloo Region, Toronto, Vaughan and Montréal.
On May 21, 2024, the International Tribunal for the Law of the Sea ("ITLOS" or the "Tribunal") issued its advisory opinion (read the opinion here) on State obligations under international law...
Canada Environment
To print this article, all you need is to be registered or login on Mondaq.com.

On May 21, 2024, the International Tribunal for the Law of the Sea ("ITLOS" or the "Tribunal") issued its advisory opinion (read the opinion here) on State obligations under international law to prevent, reduce, and control pollution of the marine environment, and to protect and preserve the marine environment (the "Advisory Opinion").

The Advisory Opinion was issued in response to a request made in December 2022 by the Commission of Small Island States ("COSIS"), an alliance of small island States committed to the development and implementation of international law concerning climate change. COSIS is responsible for a small portion of greenhouse gas ("GHG") emissions, yet it bears the brunt of climate change impacts today.

In this blog post, we examine the existing legal landscape for ocean protection, discuss the recent Advisory Opinion issued by the Tribunal, and consider the implications of this opinion both internationally and for Canada.


The world's oceans cover approximately 70% of the surface of the earth and constitute the largest livable space on the planet. As oceans transcend geographic borders, they are governed by international law, and in particular, the United Nations Convention on the Law of the Sea ("UNCLOS"). UNCLOS defines jurisdiction via maritime zones – click here to see a list of some of these definitions.

Every State has complete legislative and enforcement jurisdiction in its territorial seas – subject to the rule of international law, which entails an obligation to grant foreign ships the right of innocent passage. Beyond granting this right, coastal States have the freedom to exploit and conserve natural resources, both living and non-living, and have rights and duties related to marine pollution from vessels, land-based sources, and sea-bed activities.

The legal regime for the high seas is rapidly developing. Prior to UNCLOS, this area was subject to the freedom of the seas doctrine, which entailed expansive freedom and minimal duties for States beyond the laws of maritime war. However, with the entry into force of UNCLOS in 1994, a global and regional framework was established to protect and preserve the marine environment, and obligations were created to protect and preserve the marine environment from pollution.

Today, UNCLOS has been ratified by 169 parties. However, despite this widespread adoption, the high seas are under extreme stress from pollution, climate change, and illegal fishing. The UNCLOS framework requires States to be responsible for the ships that fly their flags and for the pollution that emanates from their jurisdiction. Penalties only arise when a State's interests have been harmed by another state. Therefore, plastic, oil, and chemical pollution coming from both land and fishing vessels (which are difficult to observe and regulate on the high seas) continue to threaten marine biodiversity with impunity.

The UN Intergovernmental Panel on Climate Change ("IPCC") warns that climate change has caused "substantial damages and increasingly irreversible loss" to ocean ecosystems, causing impacts such as sea-level rise, increasing ocean heat content and marine heat waves, ocean deoxygenation, and ocean acidification (IPCC 2019 Report on the Ocean and Cryosphere, p. 46, 79).

The extent to which the existing legal regime obligated States to address these impacts was unclear. Were States required to protect the marine environment, reduce GHG emissions, and address the deleterious effects of climate change? This uncertainty led to the submission of the request for the Advisory Opinion.


ITLOS is a dispute resolution tribunal created pursuant to UNCLOS with jurisdiction to adjudicate on submitted disputes, as well as to provide advisory opinions. Advisory opinions are a judicial function that elaborate and clarify the understanding of international obligations; though they are non-binding, they are significant authorities of international law. Advisory opinions clarify the application of rules and illustrate the legal consequences for States that flow from that application, authoritatively informing members of a legal system of their international legal obligations.

COSIS asked ITLOS to answer the following legal question:

What are the specific obligations of State Parties to the UNCLOS, 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 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?


While the Tribunal made numerous findings as to specific obligations under UNCLOS, they also made several general pronouncements that are groundbreaking advancements in international climate law.

Importantly, the Tribunal determined that anthropogenic GHG emissions fall under the definition of "pollution of the marine environment" in Article 1 of UNCLOS. The Tribunal found that GHGs, both as substances and the heat energy they increase, constitute the requisite "substance or energy" under the Convention, which are introduced by humans into the marine environment, causing deleterious effects such that they constitute pollution (paragraphs 159 – 178). This finding is significant, given that Article 194 of UNCLOS outlines measures to prevent, reduce, and control pollution of the marine environment.

The Tribunal held that Article 194 of UNCLOS established the legal framework for State obligations to:

  • prevent, reduce and control marine pollution;
  • take necessary measures to ensure marine pollution does not occur; and
  • protect and preserve threatened ecosystems, habitat, and marine life (paragraph 195).

The Tribunal then considered how States should act, and what constitutes necessary measures regarding anthropogenic GHG pollution.

First, while the Tribunal found that joint action should be pursued, it did not follow that these obligations could be discharged solely through participation in international efforts. States are required to take individual action as appropriate (paragraph 202).

Second, the Tribunal stated that necessary measures should be determined objectively, with reference to IPCC Reports as authoritative sources of the best available science. In the absence of scientific certainty, States must apply a precautionary approach to regulating marine pollution from anthropogenic GHGs (paragraphs 206-208).

Finally, the Tribunal noted that necessary measures should also be established with reference to available means and capabilities. In keeping with the common but differentiated responsibilities and respective capabilities principle established by the UN Framework Convention on Climate Change ("UNFCCC"), the Tribunal recognized that the scope and content of necessary measures will vary depending on States' economic and technical capabilities, and that States with greater capabilities must do more to reduce GHG emissions (paragraph 227). However, the Tribunal found that capability should not be used as an excuse to postpone or be exempt from action (paragraph 226).

The Tribunal also rejected the argument raised by Australia, Saudi Arabia, and India that the Paris Agreement authoritatively articulates all State obligations to regulate GHG emissions under international law. This argument contended that the UNFCCC and the Paris Agreement are lex specialis (i.e., specialized, specific law) as regards the regulation of GHG emissions, and therefore displace any general obligations under international law, such as under UNCLOS, to regulate anthropogenic GHGs. In rejecting this argument, the Tribunal found that compliance with the Paris Agreement would not satisfy State obligations to address GHG pollution under UNCLOS (paragraphs 223-224). The Paris Agreement constitutes a floor, not a ceiling, for State action. States continue to have obligations under UNCLOS that engage international responsibility to take all necessary measures to prevent, reduce, and control marine pollution from anthropogenic GHG emissions.

Beyond the obligations under Article 194 to prevent, reduce, and control anthropogenic GHGs, the Tribunal also found that UNCLOS obligates States to: (i) address GHG pollution from land, through the atmosphere, and from vessels flying their flag; (ii) take part in global and regional cooperation efforts; (iii) provide technical assistance to assist developing States in addressing GHG pollution; and (iv) undertake monitoring and environmental assessment – including assessing harmful changes caused by GHG emissions and cumulative effects.

In answer to question (b), with reference to State obligations to protect and preserve the marine environment, the Tribunal found that State obligations were broad and potentially open-ended. First, this obligation does not specify relevant harms and threats to which it applies and can therefore be invoked against degradation, including climate change impacts, ocean warming, sea level rise, and ocean acidification. While preservation could entail restoration, the Tribunal held that other international instruments could inform further measures that may be implemented, including the Paris Agreement and the Convention on Biological Diversity ("CBD") (paragraphs 385 – 388).

Finally, with reference to both questions (a) and (b), the Tribunal found that States had a stringent due diligence obligation to prevent, reduce, and control marine pollution, as well as to protect and preserve the marine environment, based on the assessment that the combined risk and severity of harm are significant (paragraphs 243, 398). Given this risk to the marine environment, the Tribunal found that States are required to take measures "as far-reaching and efficacious as possible" (paragraph 399). Notably, the Tribunal also considered that in taking necessary measures to address GHG pollution, States have a due diligence obligation to ensure that non-State actors under their jurisdiction or control comply with such measures (paragraph 396).


First and foremost, the Advisory Opinion informs State obligations under UNCLOS, providing much-needed clarity and guidance to the 169 signatories to UNCLOS – including Canada – on their treaty obligations as they relate to the oceans and climate change. State signatories are bound by international law to fulfill the obligations spelled out by the Tribunal in the Advisory Opinion. These obligations can form the basis for litigation between States before international courts and tribunals, but can also be given effect when States enact domestic law to comply with their international legal obligations.

The Advisory Opinion also constitutes a legal authority that can affect national, international, and transnational climate litigation. Previous ITLOS advisory opinions have helped develop international law. For example, in the Sub-Regional Fisheries Commission Advisory Opinion (2015), the Tribunal found that under UNCLOS, the primary responsibility for the conservation and management of living resources within exclusive economic zones rests with the coastal State. However, the Tribunal also determined that the flag state of a ship (i.e., where the ship is registered) bears the responsibility of ensuring that vessels flying their flag do not conduct illegal, unreported, and unregulated fishing in the exclusive economic zones of other States (paragraphs 104 and 119).

Canada has established a legal regime for its territorial waters under Canada's Oceans Act (the "Act"), which came into force in 1997. The Act legislated UNCLOS into Canadian law and created an ecosystem-based approach to marine management, which was considered an innovative approach at the time. In 2019, the Act was amended to increase conservation ambition, and Canada has since committed to further increase designated marine and costal protected areas from 14.66% to 30% by 2030, in line with the Kunming-Montreal Biodiversity Framework target. However, the Advisory Opinion outlined that Canada cannot fulfill its obligations to protect and preserve the marine environment through marine protected areas and conservation action alone. The Canadian government's GHG regulations, technology transfer, and international development assistance for climate mitigation now form part of its marine law regime. Furthermore, environmental impact assessments must account for the cumulative impacts of increased GHG emissions on the marine environment.

The Advisory Opinion bolsters the existence and strength of international legal obligations to take action on climate change and reduce anthropogenic GHG emissions, and could therefore function in Canadian courts similarly to the Paris Agreement (for example, as in References re Greenhouse Gas Pollution Pricing Act, 2021 SCC 11).

The Tribunal's finding that "all necessary measures" include ensuring compliance by non-State actors within a State's jurisdiction may contribute to further regulation of corporate emissions in the future. However, like the Paris Agreement, the Advisory Opinion ultimately clarified that UNCLOS contains an obligation to act on climate change and to reduce GHG emissions, but does not quantify a legally-binding amount. Fundamentally, the Advisory Opinion states that Canada has a due diligence obligation under UNCLOS to reduce emissions and protect the marine environment, alongside obligations to monitor and assess the marine environment, and to cooperate with and assist other States, particularly developing ones.


The Advisory Opinion comes at a critical time for ocean governance. On one hand, the IPCC has assessed that the ocean is "a fundamental climate regulator on seasonal to millennial time scales," and that "[a]bout a quarter of carbon dioxide (CO2) released by human activities is taken up by the ocean" (IPCC 2019 Report on the Ocean and Cryosphere, p. 78, 218). At the same time, GHG regulation and climate mitigation efforts during this decade will determine whether global warming can be limited to 1.5 degrees Celsius above pre-industrial levels (IPCC, 2019). Such outcomes have profound impacts on the oceans and the planet – determining the frequency and intensity of extreme weather, drought, sea level rise, ocean acidification, and ecosystem loss (IPCC, 2019).

Under a patchwork of domestic and international laws, the oceans remain a common resource extremely vulnerable to climate change, biodiversity loss, and pollution. The legal regime being developed to address these challenges is rapidly evolving. In 2023, an agreement on Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (the "BBNJ Agreement") was adopted under the auspices of UNCLOS. The BBNJ Agreement addresses four themes: (i) marine genetic resources, including the fair and equitable sharing of benefits; (ii) area-based management tools, including marine protected areas; (iii) environmental impact assessments; and (v) capacity-building and the transfer of marine technology. However, the BBNJ Agreement does not address climate change and ocean governance. Canada signed the BBNJ Agreement on March 4, 2024. The BBNJ Agreement has not yet entered into force. In this context, the Advisory Opinion is a key piece in the emerging ocean governance framework which uniquely addresses the nexus between the oceans and climate change. The Advisory Opinion has spelled out significant State obligations to protect and preserve the marine environment, precisely at a time when the world's oceans are undergoing major ecological crises.

The Advisory Opinion also represents a major contribution to international climate change law. Notably, two other requests for advisory opinions on international legal obligations relating to climate change were filed with the Inter-American Court of Human Rights and International Court of Justice in 2023. As the first of three anticipated advisory opinions from international judicial bodies in the near future, the Advisory Opinion will likely be an influential development in international environmental law, which both aforementioned international courts are expected to consider. While this opinion – and hopefully the ones to follow – marks a historic development in international environmental law, the onus remains on States to reduce GHG emissions and to act on climate change mitigation and adaptation.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

See More Popular Content From

Mondaq uses cookies on this website. By using our website you agree to our use of cookies as set out in our Privacy Policy.

Learn More