Last week I had the tremendous honor of providing expert testimony on the ocean effects of climate change to the International Tribunal for the Law of the Sea (ITLOS) in Hamburg, Germany. Described by some as “the Supreme Court of the Sea,” ITLOS is an independent judicial body that adjudicates and administers international maritime law (formally known as the United Nations Convention on the Law of the Sea or UNCLOS for short). 

In December, the Coalition of Small Island States (COSIS), which is co-chaired by the Prime Ministers of Antigua and Barbuda and Tuvalu, asked the Tribunal for an advisory opinion on specific obligations of countries that have signed on to UNCLOS are regarding climate change prevention and preservation of the ocean from climate change impacts. Although an advisory opinion is a nonbinding interpretation of the law, it would clarify how UNCLOS’ environmental obligations are interpreted in the future and lead to further consideration of how UNCLOS’ provisions should be enforced. Currently, 168 countries are party to UNCLOS, and this is the first time that climate change-related matters have been applied to the Law of the Sea. Last week the Tribunal began to hear oral arguments on the issue. 

My job was to distill the latest Intergovernmental Panel on Climate Change (IPCC) assessment findings and the outcomes of the recent Global Stocktake, which measured how well national climate commitments are meeting the goals of the Paris Agreement. The COSIS team had selected me from the handful of global experts involved in writing the IPCC report because of my background in ocean chemistry, physics, biology and science communication and my experience in connecting science to policy. After writing and submitting 60 pages of testimony months ago with COSIS’ filings, last week I had 30 minutes to summarize this information to the 21 Tribunal Justices—who are experts in international marine policy and law, not climate science. I had to explain in plain language how climate change is affecting the ocean and people who depend on it and what the effects of different global emissions pathways could be. My fellow IPCC report author, Dr. Shobha Maharaj, shared IPCC findings about how climate change is impacting small island nations now and what the future may hold. These scientific insights are just part of the information the Tribunal will weigh as it makes its determination. 

This case requires the Tribunal to decide on several sub-questions. First, the Tribunal oversees how UNCLOS evolves over time and must decide how the Law of the Sea should address emerging marine issues such as climate change. Second, the Tribunal must decide whether human-released carbon dioxide, and the heat that CO₂ traps, constitute marine pollution. Third, it must also consider how UNCLOS and other international policies, like the Paris Agreement and the Biodiversity Beyond National Jurisdictions (BBNJ) Treaty, complement each other. 

It’s hard to explain the weight of the moment—presenting to the Tribunal was unlike any other presentation I’ve given. The justices listened attentively from a tall, imposing curved dais while the unusually muggy weather outside reminded us that climate change is even touching Hamburg. Presenters before me—including the co-chairs of COSIS and a lawyer who’s also a youth leader, a Tuvaluan, and a mother—spoke movingly about what their communities and families stand to lose. Like other times, I was under pressure to share a vast amount of information simply, quickly and objectively. But this time truly moved me. So much was at stake; so many international policy experts had come together to provide input; so many people were listening. During my testimony, as I listed the many marine ecosystems that are at a minimum at moderate risk from climate change under a middle-of-the-road emissions future—estuaries, salt marshes, mangrove forests, seagrass meadows, kelp forests, sandy beaches, rocky shores, epipelagic systems, eastern boundary upwelling systems and seamount systems—I was fighting back tears. Grief about what we will lose if we don’t quickly curb climate change threatened to burst through my carefully composed scientific presentation. I paused. I thought of the thousands of climate experts whose work I was sharing and all those who depended on me to present the scientific evidence to the Tribunal. I breathed deeply—once, twice—and steadied my voice. I made it through. 

Countries party to UNCLOS made oral arguments to the Tribunal about this case by September 25. Afterwards, the Tribunal will deliberate and provide their opinion around March 2024. It’s anyone’s guess how the Tribunal will rule. So far, countries have largely agreed with COSIS’ argument that carbon dioxide and heat are a type of pollution, and that UNCLOS and Paris Agreement goals are complementary. How the Tribunal’s ruling will alter international marine and climate policies is anyone’s guess.

I often explain my job to people as making sure that the best available science can be reflected in marine policy. There’s nothing quite like having two sitting Prime Ministers and an Attorney General from three different nations thank you for doing your job. I’m thrilled to have been asked to provide the Tribunal with the latest scientific information to support their decision-making. I, and countless others, can’t wait to learn the outcome of this precedent-setting case. It’s been an enormous privilege to bring science into the discussion.