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Greenhouse gases are ocean pollution, international court rules – Expert Reaction

The International Tribunal for the Law of the Sea has ruled that greenhouse gas emissions are a form of marine pollution. 

The ruling is an ‘advisory opinion’ and not legally binding, but it means that obligations to prevent, reduce and control marine pollution also apply to atmospheric greenhouse gas emissions under the UN Convention on the Law of the Sea.

The case was brought to the Tribunal by nine Pacific and Caribbean island nations seeking better protection from climate change.

The SMC asked experts to comment.

Dr Dalila Gharbaoui, Postdoctoral Climate Crisis Research Fellow, Macmillan Brown Centre for Pacific Studies, University of Canterbury, comments: 

“A major milestone for international climate justice led by Small Island States at the forefront of the sea level rise threat on their territories. The opinion is advisory but could be replicated as precedent for other cases and likely to inform future climate justice cases in national, regional and international courts.  This historical win is a critical step towards protecting oceans across the world and mitigating the effect of carbon dioxide on a global scale.

“Countries now have an obligation to take measures to mitigate the impacts of carbon dioxide on oceans. This decision is instrumental in shaping the scope of future climate litigation involving greenhouse gas emissions and provides an opportunity to raise awareness and recentre focus on protecting our oceans as an essential part of our sustainable futures.

“Scientific knowledge on greenhouse gas emissions absorbed by the ocean considered as marine pollution isn’t new, but it is always a victory when decisions are made towards bridging the gap between sciences and practical policy and legal outcomes; even if it is a slow process, each step matters.

“This decision is also of symbolic importance as it extends the scope of the Paris climate agreement towards obligations for countries to protect their marine environments and Oceans. As always, the issue of how this will be practically implemented by States is there but nevertheless it is one more “drop in the ocean” in the ongoing battle for climate justice, and each step matters.”

No conflict of interest

Dr Karen Scott, Faculty of Law, University of Canterbury, comments:

“This is an important decision that has confirmed that greenhouse gas emissions comprise ‘pollution’ for the purposes of the law of the sea convention and that the obligations under the Convention to ‘prevent, reduce and control pollution of the marine environment’ apply to activities causing greenhouse gas emissions on land, from ships and through the atmosphere.

“The Tribunal confirmed that the obligation is not one of result but an obligation of conduct. States must take best efforts in respect of their measures on the basis of due diligence, but the standard of due diligence is ‘stringent’ in light of the risks climate change and ocean acidification pose to the marine environment.

“The Tribunal drew extensively on the climate regime and other instruments in terms of identifying what types of measures states should take, but importantly, the Tribunal found that the obligations under the law of the sea convention are satisfied by only complying with obligations under the climate change regime. The Tribunal did not specify exactly what measures states should take but said that factors in developing measures included science, international rules on climate change as well as the capacity of the state developing those measures. The Tribunal went on to find a number of other general obligations to protect and preserve the marine environment applied to climate change and ocean acidification including obligations relating to cooperation, environmental assessment and monitoring and fisheries management.

“Although this decision is advisory only, and technically addresses only the Commission of Small Island States on Climate Change and International Law (COSIS) and its members, it is significant in that it is the first international court to apply law of the sea obligations to protect the marine environment in the context of climate change and ocean acidification. It makes it clear that states have obligations under the law of the sea convention to address climate change and ocean acidification in support of but independently of the climate regime. This decision will have implications for all states, including New Zealand.”

No conflict of interest

Our colleagues at the Australian Science Media Centre also gathered comments:

Dr Constantinos Yiallourides, Senior Lecturer in International Law and Deputy Director of the Centre of Environmental Law (CEL) at Macquarie University, comments:

“The connection between oceans and climate change is clear and undisputed. Oceans control the climate system by absorbing heat and carbon dioxide, while climate change from greenhouse gas (GHG) emissions causes ocean acidification, ocean warming and sea level rise, threatening many low-lying island nations. These island nations are urgently seeking protection under international law.

“A crucial step in this effort was achieved on 21 May 2024. For the first time, an international court addressed the obligations of the 168 States parties to the UN Convention on the Law of the Sea (UNCLOS), including Australia, concerning climate change impacts on the oceans, such as ocean acidification, and sea level rise. The International Tribunal for the Law of the Sea (ITLOS) ruled unanimously that anthropogenic GHG emissions absorbed by the oceans constitute ‘pollution of the marine environment’ due to their harmful effects on marine ecosystems and marine biodiversity. This means GHG emissions, introduced indirectly into the oceans, whether from CO2-emitting industrial facilities, airplanes, or vessels, whether land-based or ocean-based, are now legally recognised as a form of ocean pollution that must be mitigated, controlled, and eventually prevented.

“The significance of this finding should not be underestimated, as it triggers States’ international law obligation to take ‘all necessary measures’, individually and collectively, against GHG emissions. In adopting these necessary measures, States should follow the science, notably the scientific conclusions of the Intergovernmental Panel on Climate Change (IPCC). This includes assessing the cumulative carbon footprint of all planned projects on the oceans before allowing them to go ahead.

“It also includes an obligation to take all necessary actions to address the impacts of climate change on developing and climate-vulnerable countries, including low-lying island nations, by providing them with economic and other assistance.

“While the ITLOS ruling is not legally binding, it holds immense authoritative value in interpreting and applying States’ environmental obligations under UNCLOS to modern climate change challenges. It directs States and courts, both national and international, to apply and enforce these obligations consistently to combat climate change.

“It is likely that other international and national courts will consider the ITLOS advisory opinion when making their own assessments on climate-related cases, including challenging the legality of high-emitting activities due to their potential carbon footprint on the oceans.

“ITLOS’ ruling is expected to influence climate proceedings at the International Court of Justice and the Inter-American Court of Human Rights, as well as over 2,000 domestic climate litigation cases seeking to hold governments and corporations accountable for inadequate climate action.”

Conflict of interest statement: Constantinos has declared he is a member of several energy-focused research groups at Macquarie and Research Leader in Law of the Sea at the British Institute of International and Comparative Law. He has provided advice to governments and institutions and has had research funded by several organisations including private and third parties.