Precedent-Setting Advisory Opinion on Climate Change: An Urgent Call for Action

On May 21, 2024, the International Tribunal for the Law of the Sea delivered a groundbreaking advisory opinion on state parties’ climate change obligations under the United Nations Convention on the Law of the Sea (UNCLOS).

The unanimous opinion found that state parties have legal obligations to implement measures to prevent, reduce and control greenhouse gas (GHG) emissions, including by enacting laws and regulations. In developing those measures, states must consider the best available science and international treaties like the Paris Agreement and the United Nations Framework Convention on Climate Change (UNFCCC).

This is the first time an international court has issued such a decision, and it could have major consequences for states in the global effort to address the climate crisis. The landmark decision has significant implications for Canada, a party to the Convention, reinforcing its obligations under international law to combat climate change. As Canadians brace for another potentially devastating wildfire season, the timing of this opinion couldn’t be more critical.


Canada ratified UNCLOS in 2003. Legally binding on parties, the Convention sets out states’ rights and responsibilities regarding the use and environmental protection of oceans. Those rights and responsibilities include the following:

  • States must protect and preserve the marine environment (Article 192).
  • States must take necessary measures to prevent, reduce, and control marine pollution from any source (Article 194).
  • Those measures must include laws and regulations to prevent, reduce and control marine pollution from land-based sources, taking into account internationally agreed rules and standards and recommended practices and procedures (Article 207).
  • States must enforce their laws and regulations regarding marine pollution, and must also adopt laws, regulations and other measures to implement applicable international rules and standards (Article 213).

While we tend to think of GHGs as an air pollutant, the ocean absorbs about 30% of the carbon dioxide that burning fossil fuels spews into the atmosphere, resulting in increased ocean acidity that harms sea life. It also absorbs much of the heat generated by the blanket of greenhouse gases in the atmosphere. As a result, GHGs are harming the world’s marine environment on a massive scale.

In December 2022, the Commission of Small Island States referred two questions to the Tribunal seeking clarification on parties’ obligations under UNCLOS regarding climate change and marine protection. The questions (paraphrased) were:

  1. What are state parties’ obligations to prevent, reduce and control marine pollution caused by anthropogenic greenhouse gas (GHG) emissions? and
  2. What are state parties’ obligations to protect and preserve the marine environment in relation to climate change impacts, including ocean warming, sea level rise and ocean acidification?

What the Tribunal Found

The Tribunal found that state parties have a legal obligation to implement measures to prevent, reduce, and control GHG emissions, as well as measures to protect and preserve oceans from climate change impacts. These obligations include a duty to adopt laws and regulations to prevent, reduce and control those emissions.

As a starting place, the Tribunal recognized that the release of GHG emissions into the atmosphere constitutes marine pollution under UNCLOS. The Convention defines “pollution of the marine environment” as:

[T]he introduction by man, directly or indirectly, of substances or energy into the marine environment, including estuaries, which results or is likely to result in such deleterious effects as harm to living resources and marine life, hazards to human health, hindrance to marine activities, including fishing and other legitimate uses of the sea, impairment of quality for use of sea water and reduction of amenities (Art 1(1)(4)).

To meet this definition, (1) GHGs must be a substance or energy; (2) they must be directly or indirectly introduced by humans into the marine environment; and (3) introducing them must result or be likely to result in deleterious effects.

The Tribunal found that anthropogenic GHGs meet all three criteria. Gas is a substance, and GHGs are produced in large quantities “by man.” And as discussed above, carbon dioxide dissolves in the ocean and is therefore directly introduced by humans into the marine environment, while the ocean also stores the heat, a form of energy, that is trapped by GHGs (paras 164-65, 172). As a result, introducing GHGs into the marine environment causes ocean warming, sea level rise and ocean acidification, and the science is clear that these consequences have significant deleterious effects on the marine environment (para 175).

The fact that GHGs constitute “pollution of the marine environment” gives rise to the legal obligation that UNCLOS imposes on state parties to prevent, reduce, and control emissions pollution.

Article 194 requires states to take all necessary measures to prevent, reduce and control marine pollution from “any source,” including “the release of toxic, harmful or noxious substances, especially those which are persistent, from land-based sources, from or through the atmosphere or by dumping” (Art 194(3)(a)). States must ensure that any pollution from “activities under their jurisdiction or control” does not harm other states or their environment and does not spread beyond states’ jurisdictional boundaries (Art 194(2)). Article 194 also requires states to take measures to protect fragile ecosystems and at-risk species from marine pollution (Art 194(5)).

Thus, states have an obligation to take “all necessary measures” to prevent, reduce and control GHGs that they release or permit to be released into the atmosphere. The Tribunal held that the precautionary principle should help identify what “necessary measures” means (para 213). The precautionary principle posits that states should prevent pollution even where the science is not conclusive that the pollution is harmful, or that measures to prevent it will work. The Tribunal found that “necessary measures” therefore include any measures that make it possible to prevent, reduce and control marine pollution caused by GHGs (para 203).

Since UNCLOS requires states to adopt “internationally agreed rules, standards and recommended practices and procedures” (Art 207), the measures undertaken by states should also be informed by the Paris Agreement and UNFCCC. These agreements require states to pursue efforts to do their fair share towards limiting global temperature rise to within 1.5°C. Also, states with greater means (like Canada) must do more to reduce their emissions than states with fewer means and capabilities (paras 222, 227). States’ GHG mitigation policies should be harmonized, suggesting the need for states to have credible climate plans (para 230).

What is more, states must act with “due diligence” in taking necessary measures to prevent, reduce and control GHGs. According to the Tribunal, the standard of due diligence is stringent, and:

The obligation of due diligence requires a State to put in place a national system, including legislation, administrative procedures and an enforcement mechanism necessary to regulate the activities in question, and to exercise adequate vigilance to make such a system function efficiently, with a view to achieving the intended objective. (para 235)

In other words, measures include establishing national legislation and harmonizing policies (such as through credible climate plans) for reducing their GHGs, and states like Canada must do their due diligence in ensuring their measures constitute their fair share in the global effort to limiting temperature rise to 1.5°C.

Implications for Canada

Canada, as a State Party to UNCLOS, must heed the Tribunal’s opinion. The opinion confirms that Canada is legally bound to take robust action against climate change. That action must include strengthening Canada’s climate target to one that represents Canada’s fair share of emissions, enhancing its climate plan and implementing all measures necessary for meeting its target.

Given the outsized GHGs of the oil and gas industry, those measures must include a stringent oil and gas emissions cap that ensures the industry does its part in the national effort to reduce our emissions.

Canada has the longest coastline in the world, facing massive marine climate costs, from the death of marine life to rising sea levels that threaten to cost coastal communities billions of dollars. Inland, we face yet another year of wildfires and drought across Canada, threatening lives, ecosystems, and communities. The urgency of climate action cannot be overstated.

The Tribunal’s opinion serves as a wake-up call for elected leaders and the oil and gas industry. Climate change directly impacts marine ecosystems and exacerbates extreme weather events like wildfires. Those who perpetuate climate denialism, such as by claiming climate change is not an underlying cause of wildfires or obstructing strong climate action, would have Canada run afoul of international law and continue to put our ocean at risk. The future of the marine environment demands collective responsibility and immediate action.

Canada, as a coastal nation, must lead by example, demonstrating its commitment to safeguarding the ocean and combating climate change. Let this opinion be a clarion call for decisive action—our planet’s future depends on it. 🌎🔥🌊

— Anna Johnston, Staff Lawyer

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