Belém is located on a peculiar yet stunning edge of the globe, where the Amazon slowly and brownly empties into the Atlantic. It was an almost too obvious choice for a climate summit. The rainforest, Indigenous rights, and the timelines for fossil fuels, which always seem to move forward by five years, were among the topics discussed by the delegates. During COP30, the word “deep” was frequently used to describe deep divisions, deep disappointment, and deep concern. But the actual deep sea hardly emerged at all.
It is worthwhile to sit with that absence. Roughly 90% of the ocean is below 200 meters, a location that most of us will never see and that most negotiators seem to never consider. It has stored more than thirty percent of our carbon emissions and absorbed about ninety percent of the excess heat that humans have produced since the Industrial Revolution. Nevertheless, the deep sea was not mentioned once in the final decision texts that were hammered out under the muggy Pará sky. Not one.
Observing these summits year after year gives one the impression that the ocean has at last forced its way into the space. For that, Brazil is truly deserving of praise. As host, it was one of only a few nations to incorporate the ocean into its Nationally Determined Contribution. During one session, Dr. Marinez Scherer, COP30’s Special Envoy for the Ocean, stated unequivocally that action with and for the ocean is necessary to address the climate crisis. The line touched down. Everyone then proceeded to the following item on the agenda.
The actual carbon storage machinery resides in the deep. What scientists refer to as the “biological pump” is powered by tiny, mostly unidentified organisms that transport carbon from the sunlit surface to the chilly, dark seafloor, where it can remain trapped for centuries. It’s a low-key, antiquated process that doesn’t use press releases or subsidies. And it’s starting to falter. The increasing damage to Arctic deep-sea ecosystems—warming, acidification, and oxygen loss reaching depths that have seen virtually no change for millennia—was highlighted by new research released during the conference. Under continued warming, it is predicted that over 80% of deep-sea biodiversity hotspots, such as sponge beds, seamounts, and cold-water coral reefs, will drastically decline.
Then there’s the active changes that people are making to the area. Ecosystems that took thousands of years to form can be destroyed in a single bottom trawler pass, turning cold-water corals into rubble in a matter of minutes. Whales, sharks, and turtles use seamounts as underwater stepping stones; we are blowing up the staircase. The strange new field of marine geo-engineering, which sounds reasonable in a slide deck but is far less reasonable in practice, and the impending possibility of industrial-scale deep-sea mining both add another layer of risk.
A tiny, easily missed flicker of progress was present. The social and environmental hazards of unsustainable critical mineral extraction were recognized for the first time in the draft COP text. The final document, which tells a silent tale about who has power in these rooms, did not include that language. Even though the conversation isn’t quite over, the fact that it showed up at all indicates that it is starting.
The solution is not enigmatic. Governments can pursue the goal already indicated by IUCN Motion 32 and ultimately prohibit bottom trawling on seamounts before the UN bottom fisheries review next year. In 2026, they can definitively reject deep-sea mining instead of using another ambiguous “maybe.” The deep ocean is the planet’s largest and least understood climate ally. Instead of viewing it as a side effect, they should treat it as such.
As we watch Belém’s lights flicker out, it’s difficult to ignore the fact that we continue to design climate policy as though the ocean ends at our ankles.
