HAMBURG — In its historic unanimous Advisory Opinion delivered on May 21, 2024, the International Tribunal for the Law of the Sea (ITLOS) fundamentally transformed ocean governance.
At the request of the Commission of Small Island States on Climate Change and International Law (COSIS), the Tribunal ruled that anthropogenic greenhouse gas emissions into the atmosphere legally constitute pollution of the marine environment under the UN Convention on the Law of the Sea (UNCLOS).
1. The Statutory Bridge: Article 1(1)(4) UNCLOS
UNCLOS Article 1(1)(4) defines marine pollution as:
“The introduction by man, directly or indirectly, of substances or energy into the marine environment… which results or is likely to result in such deleterious effects as harm to living resources and marine life…”
ITLOS applied a strict literal interpretation:
- Carbon dioxide is a substance;
- Thermal energy (excess ocean heat absorption) is energy;
- Both are introduced indirectly by human activity through the atmosphere, causing documented deleterious effects including ocean acidification, deoxygenation, and coral reef mortality.
By this determination, the entirety of UNCLOS Part XII—the most robust environmental protection framework in international law—now governs atmospheric greenhouse gas emissions.
2. Article 192 and the High Standard of Due Diligence
Under Article 192, states have the general obligation to “protect and preserve the marine environment”. Under Article 194(1), states must take all necessary measures to prevent, reduce, and control marine pollution.
The Tribunal established that this duty is an obligation of conduct governed by strict due diligence:
- States cannot satisfy their UNCLOS commitments merely by complying with national emissions goals under the Paris Agreement.
- Due diligence must be determined objectively based on the best available science (specifically IPCC assessments) and the international consensus to limit global heating to 1.5°C.
While recognizing Common But Differentiated Responsibilities (CBDR), the Tribunal emphasized that developing coastal states’ lack of capability does not excuse major industrialized nations from deploying their full technical and economic capacity to curtail emissions.