What are the Legally Binding Obligations of States in Respect of Climate Change?

By Payam Akhavan and Rozemarijn Roland Holst

One of the most remarkable developments in the history of international law is the leadership of small island States in addressing the obligations of States in respect of climate change. This has taken the form of two complementary requests for advisory opinions from the International Tribunal for the Law of the Sea (ITLOS) in December 2022 and the International Court of Justice (ICJ) in March 2023.

These unprecedented initiatives were born out of long-standing frustration with the lack of progress on climate change mitigation, adaptation, and loss and damage under the 1992 UN Framework Convention on Climate Change (UNFCCC) and the 2015 Paris Agreement. Small island States are the canary in the coal mine. They face existential threats from rising sea levels and extreme weather events, and some could become uninhabitable or simply disappear under the waves in the near future.

In recent times, they have become aware that many of their demands are already part of international law, including the general obligation of major polluters to prevent transboundary harm. While advisory proceedings are not a solution to climate change, they are an important piece of a larger puzzle. They can help reframe the annual negotiations under the UNFCCC and the Paris Agreement in terms of what is legally required, rather than what is politically expedient.

One of the protagonists of this campaign is the Commission of Small Island States on Climate Change and International Law (COSIS). It was established on 31 October 2021 at the 26th session of the Conference of the Parties (COP 26) to the UNFCCC in Glasgow by Antigua and Barbuda and Tuvalu. Palau, Niue, Vanuatu, Saint Lucia, Saint Kitts and Nevis, Saint Vincent and the Grenadines, and The Bahamas have since become members of COSIS.

The COSIS Agreement authorizes the Commission to request an advisory opinion from ITLOS on legal questions within the scope of the 1982 UN Convention on the Law of the Sea (UNCLOS) – also known as “the Constitution of the Oceans.” The questions COSIS submitted to ITLOS on 12 December 2022 concern States’ obligations under UNCLOS to protect and preserve the marine environment from the impacts of climate change and ocean acidification.

Around the same time, Vanuatu was spearheading the initiative for the UN General Assembly (UNGA) to adopt a resolution to request an advisory opinion on climate change from the ICJ. Unlike ITLOS which allowed for a request to be made pursuant to an international agreement, the ICJ requires a resolution of a UN organ or specialized agency. Contrary to the sceptical view that small island States could not succeed in such an enormous undertaking, the UNGA adopted the resolution requesting an advisory opinion from the ICJ by consensus on 29 March 2023. The questions submitted to the ICJ are broader in scope than those before ITLOS – which is a specialized tribunal – and include additional dimensions of human rights, transboundary harm under general international environmental law, and state responsibility for breaches of international obligations.

The relationship between the two requests is one of complementarity, as is evidenced by Vanuatu becoming a member of COSIS and by COSIS’ participation in the ICJ proceedings. The wide participation in both proceedings is further testament to their significance. An unprecedented number of 42 States and international organizations have made written submissions to ITLOS, and 91 States and international organizations are participating in the ICJ proceedings. In addition, numerous non-governmental organizations (NGOs) have made submissions that, although not formally part of the case file, have been published on the ITLOS website.

The sequencing of the two proceedings is also significant. ITLOS was the first to speak on the matter when it delivered its unanimous advisory opinion on 21 May 2024. In doing so, the ITLOS opinion laid several important foundations which are likely to shape the ICJ’s jurisprudence, consistent with its role in the harmonization of international law as the principal judicial organ of the UN.

It is noteworthy that while the ICJ has a wider mandate to address different dimensions of climate change, the ITLOS opinion on protection of the marine environment addresses a fundamental aspect of the Earth’s climate system. The ocean has absorbed a quarter of atmospheric carbon dioxide (CO2) emissions and 93% of excess heat. As UNCLOS governs the protection of the marine environment from all sources of pollution, including land-based and atmospheric pollution, the questions answered by ITLOS are key to ensure, on the one hand, the effective protection of the ocean from climate impacts and, on the other hand, the preservation of the balancing functions of the ocean in the climate system. ITLOS’ main findings can be summarized as follows:

Greenhouse gas (GHG) emissions into the atmosphere constitute “pollution of the marine environment” for the purposes of UNCLOS. This triggers a range of substantive and procedural obligations set out in UNCLOS Part XII.
States have specific obligations under UNCLOS Article 194 to take all necessary measures to prevent, reduce, and control marine pollution from anthropogenic GHG emissions. These measures should be determined objectively, informed, inter alia, by the best available science, relevant rules and standards contained in other treaties, and the temperature goal of 1.5°C. The obligation to take all necessary measures is one of due diligence and is stringent, given the serious risks of irreversible harm. The standard can be even more stringent in cases of transboundary pollution. Implementation of the obligation may vary according to States’ capabilities and available resources.
States have an obligation under UNCLOS Article 192 to protect and preserve the marine environment. This obligation is of dual significance in that it requires mitigation as well as resilience-enhancing and adaptation measures, which may include measures to restore the marine environment.

A particularly important takeaway from the ITLOS advisory opinion is that obligations under UNCLOS cannot be satisfied simply by complying with commitments under the Paris Agreement. While obligations under different regimes may complement and inform each other, the Tribunal stressed that these are separate agreements, with separate sets of obligations.

ITLOS’ affirmation that the Paris Agreement does not supersede UNCLOS on matters of marine pollution from anthropogenic GHG emissions is all the more pertinent because States’ voluntary commitments in their nationally determined contributions (NDCs) under the Paris Agreement and its ambition-raising mechanism are falling well short of what is required to meet the 1.5°C temperature goal by 2100 in order to avert catastrophic harm. With current efforts under existing NDCs, the world is on track to hit 2.8°C by the end of the century, as underlined by the 2023 Global Stocktake and the 2023 NDC Synthesis Report. The reason why going beyond the climate change regime is so important is because this model of global governance – based entirely on voluntary and non-enforceable commitments – has clearly failed to make the necessary progress over the past thirty years.

ITLOS’ clarification of the relationship between the climate change regime and UNCLOS is also important with an eye to the ICJ proceedings where the relationships between various branches of international law and the UNFCCC and Paris Agreement will be a central issue. While international negotiations under the UN climate regime are imperative to navigate the complexities of climate change, the ITLOS and ICJ advisory opinions could potentially shape this process by clarifying the existing legally binding obligations of major polluters to avert catastrophic harm caused by climate change and to make reparations for breaches of such obligations.

One thing is clear, the Earth will not wait for humankind to take the necessary action. The challenge is to appreciate that international law must be informed by irrefutable scientific evidence and that compliance with legally binding obligations is not merely desirable, but a matter of our common survival. Put differently, the international law of climate change reflects the laws of the natural world, which the Earth will no doubt vigorously enforce.

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Payam Akhavan is Human Rights Chair and Senior Fellow at Massey College, University of Toronto, Member of the Permanent Court of Arbitration, and legal counsel to COSIS.

Rozemarijn Roland Holst is a Lecturer in International Environmental Law, University of Edinburgh, and legal advisor to COSIS.

This Guest Article 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.