Strengthening the Climate-Ocean Nexus

How BBNJ and the ICJ Advisory Opinion Are Reshaping Global Governance

Author: Angelique Pouponneau, Research Fellow with Global Ocean Accounts Partnership

We stand at a pivotal moment in international environmental law—one where the ocean and climate are finally being recognized not as separate challenges, but as interconnected systems requiring integrated legal responses.

Our oceans absorb over 90% of excess heat and 30% of carbon dioxide from human activities. Yet for decades, ocean and climate governance have operated in silos. All that is changing now, thanks to two groundbreaking legal developments that are reshaping how we approach planetary stewardship.

The BBNJ Agreement: Climate-Smart Ocean Governance

In June 2023, the world adopted the Agreement on Biodiversity Beyond National Jurisdiction—the BBNJ Agreement—our first comprehensive framework on the conservation and sustainable use of marine biodiversity in areas beyond national jurisdiction. But this treaty is far more than a biodiversity instrument. The BBNJ Agreement (aka the High Seas Treaty) addresses core issues in an integrated manner, bridging the ocean, climate, and biodiversity crises.

The Agreement explicitly embeds climate considerations into its foundation. In the principles and approaches section that guides implementation, there's a commitment to "an approach that builds ecosystem resilience, including to adverse effects of climate change and ocean acidification, and also maintains and restores ecosystem integrity, including the carbon cycling services that underpin the role of the ocean in climate."

One of the key objectives for area-based management tools is to "protect, preserve, restore and maintain biological diversity and ecosystems, including with a view to enhancing their productivity and health, and strengthen resilience to stressors, including those related to climate change, ocean acidification and marine pollution."

When we establish marine protected areas under BBNJ, we're not just protecting species—we're safeguarding blue carbon ecosystems. 

When we mandate environmental assessments, we're ensuring climate considerations guide all high seas activities. The Agreement also includes robust provisions on capacity-building and technology transfer to address "stressors on the ocean that affect marine biological diversity of areas beyond national jurisdiction, including the adverse effects of climate change, such as warming and ocean deoxygenation, as well as ocean acidification."

But here's the fundamental truth: without healthy oceans, we cannot achieve the Paris Agreement's 1.5°C temperature limit. And without achieving the 1.5°C temperature limit, we may jeopardize any wins from marine protected areas. The interdependence is absolute.

The ICJ Game-Changer

July 23, 2025 will be remembered as a watershed moment for climate law. The International Court of Justice (ICJ) delivered its advisory opinion on climate obligations, and the ruling affirms what many legal scholars and advocates have long argued: states have binding obligations to prevent climate harm and can be held responsible for failing to do so.

The Court was unequivocal: the ICJ determined that the 1.5°C temperature target is legally binding under the Paris Agreement and that all states, particularly the largest emitters, must take ambitious mitigation measures in line with the best available science.

What makes this ruling transformative for ocean governance is the Court's emphasis that treaties must be read as part of an interlinked system of law.

Climate change treaties cannot be treated in isolation—they must be read in the context of the United Nations Convention on the Law of the Sea (UNCLOS), other environmental treaties, and customary law.

The Powerful Synergy

The ICJ ruling doesn't just strengthen climate law—it turbocharges the BBNJ Agreement. The Court emphasized that the duty to cooperate is not a matter of choice but a pressing need and legal obligation. The BBNJ Agreement embeds this principle throughout, including the need to cooperate on marine scientific research and transfer of marine technology.

This creates what legal experts call "a symbiotic relationship" between these frameworks. When states implement BBNJ's area-based management tools, they're now legally required to consider climate impacts. This will increase the movement to resolve certain debates about whether activities in areas beyond national jurisdiction can contribute to Nationally Determined Contributions (the national climate action plans submitted by each country under the Paris Agreement).

The Court also ruled that "COP decisions are relevant to treaty interpretation. That keeps agreements like BBNJ alive and adaptable." This means BBNJ will evolve with our growing understanding of climate science, ensuring ocean protection keeps pace with climate urgency. The critical question now is: at what points will we activate this principle, and what will its operationalization look like?

The Path Forward

As we head toward COP30 in Brazil—where the Amazon meets the Atlantic—we have unprecedented legal clarity. Brazil, which demonstrated clear interest in ocean issues at COP29 and included ocean-based measures in its revised Nationally Determined Contribution, will play a crucial role with its COP30 Presidency.

The ICJ has now made clear that adaptation can no longer be treated as an option, but as a legal obligation—and healthy oceans are our greatest adaptation infrastructure. 

Adaptation and mitigation strategies will need to account for the impacts of climate change on people, the economy, and the ocean environment. With ocean accounting we have the framework to make decisions based on a structured compilation of economic, social and environmental data. With this we can make visible the vital connection between human wellbeing and ocean health in shaping an equitable response to climate change.

Moving Beyond Silos

We have the legal tools. We have scientific evidence. We have data. We have international courts affirming our obligations. What we need now is the political will to implement these frameworks as the integrated system they were designed to be.

The ocean doesn't recognize the boundaries between our legal agreements. Neither should we. The future of climate stability depends on how quickly we can translate these legal breakthroughs into concrete protection for our blue planet.

The time for siloed thinking is over. The era of integrated ocean-climate governance begins now.