The deep sea and the Arctic must be included in efforts to tackle climate change

Animals on the seafloor, such as corals and crinoids, take carbon into their bodies. When they die, this carbon is taken into seafloor sediments, where it is stored for hundreds and even thousands of years. (Schmidt Ocean Institute/Erik Cordes), CC BY

This year’s COP30 comes after the international Agreement on Marine Biological Diversity of Areas beyond National Jurisdiction (BBNJ) finally acquired the required number of ratification votes by United Nations member states.

The treaty, effective from January 2026, is the first global agreement for marine areas beyond national jurisdictions, with a direct reference to climate change risks in its legal text. Its ratification comes at a crucial time for marine environments.

The momentum of COP30 and the BBNJ treaty creates a unique opportunity to further integrate the ocean, particularly the deep sea, into the climate agenda. By connecting the BBNJ under the United Nations Convention on the Law of the Sea and the 2015 Paris Agreement, UN member states now have the tools to better conserve the deep sea’s biodiversity and its role in the global carbon cycle.

The deeps sea’s role in our climate

The deep sea (areas deeper than 200 metres) covers more than half our planet’s surface and accounts for over 90 per cent of the ocean’s volume. It is Earth’s largest long-term carbon sink.

Since the Industrial Revolution, the deep sea has absorbed roughly 30 per cent of human-caused carbon dioxide emissions and about 90 per cent of excess heat, significantly slowing warming and buffering the planet against even more catastrophic impacts.

The deep sea stores 50 times more carbon than the atmosphere and 20 times more than all terrestrial plants and soils combined. It helps regulate the Earth’s climate and its importance in fighting climate change is immense, stretching from pole to pole.

The polar regions support essential climate functions. The Southern Ocean around Antarctica absorbs approximately 40 per cent of the global oceanic uptake of human-generated carbon. The opposite pole, the Arctic Ocean, is facing some of the most immediate threats from climate change.

Against this backdrop, COP30 is hosting an unprecedented number of Indigenous people, with around 3,000 participants. Inuit, Sámi, Athabaskan, Aleut, Yupiit and other Arctic and global Indigenous leaders are voicing the need for climate policy to reflect local knowledge, rights and values in line with claims by Arctic states to sovereignty and stewardship.

However, discontent exists given the lack of representation of Indigenous people in COP30 negotiations. More than 70,000 people participated in the parallel People’s Summit which produced the Declaration of the Peoples’ Summit towards COP30. The declaration calls for more equitable solutions to climate change that include Indigenous and other communities.

Indigenous Peoples already co-create scientific management of marine protected areas, such as the Primnoa resedaeformis coral habitats and glass sponge reefs in Nova Scotia. However, more efforts are needed to reach the 30x30 target to designate 30 per cent of the Earth’s land and oceans as protected areas and achieve the goals of the Paris Climate Agreement.

Closing the ocean gap

Recent sessions of the United Nations Framework Convention on Climate Change (UNFCCC) have focused on co-ordination across major international agreements like the BBNJ. These sessions, along with the latest vulnerability assessments from the Intergovernmental Panel on Climate Change and UNFCCC’s Ocean Climate Change Dialogues, have urged parties to align ocean actions with climate commitments and close measurement and reporting gaps.

In the summer of 2024, Brazil and France started the Blue NDC Challenge, encouraging countries to include ocean-based climate solutions in their National Determined Contributions (NDCs) and National Adaptation Plans.

The UNFCCC requires NDCs to increase carbon uptake rather than historical storage to mitigate. Carbon uptake is the process, activity or mechanism by which natural sinks remove CO2 from the atmosphere. On the other hand, National Adaption Plans may protect deep-sea ecosystems and their biological pump roles.

While recent syntheses show that about 75 per cent (97 out of 130 coastal states that have submitted their NDCs) of UN member states now reference marine and coastal actions in their NDCs, the formal mechanisms for implementing adaptation efforts that include the ocean are lagging behind.

Of the roughly 100 climate indicators being considered at COP30 to monitor the progress of the Paris Agreement’s global goal on adaptation, only 14 include marine or ocean dimensions, with the majority focusing on coasts or shallow waters.

Although those with marine dimensions could be extended to include the deep sea, a persistent omission of deep-sea ecosystems risks undermining both mitigation and adaptation goals. While the final indicators are yet to be determined, it’s critical to ensure that deep-sea ecosystems are explicitly incorporated.

The global stocktake — the Paris Agreement’s process to evaluate the world’s climate action progress — determines if countries are meeting goals and identifies gaps. The stocktake must also identify the deep ocean and deep-sea life specifically, and elaborate on appropriate ocean-based climate actions, comparable to elaborations on the need to halt and reverse deforestation and forest degradation.

Supporting the Paris Agreement

photo of bivalves and yeti crabs under water — A hydrothermal vent community of bivalves and yeti crabs (Kiwa hirsuta). Chemosynthesis converts inorganic compounds like sulphide/methane via microbial communities where light is unavailable in the deep sea. (Schmidt Ocean Institute/Erik Cordes)

Emerging activities, misguidingly branded as helping the energy transition — like deep-sea mining — further threaten oceans by causing irreparable damage to the sea floor and in the water column.

Geoengineering technologies to remove excess CO₂ from the atmosphere are so far costly and ineffective, but may be necessary to meet the Paris Agreement’s 1.5 C target. However, marine-based technologies may disrupt seafloor habitats, alter ocean chemistry and disrupt the natural carbon cycle in unpredictable ways.

The largest uncertainties in future climate projections stem from potential changes in ocean circulation and biological activity that could reduce the ocean sink efficiency. Even if emissions are stopped, a substantial fraction (20 to 40 per cent in some models) of emitted CO₂ will remain in the atmosphere for a millennium or longer, persisting until slow geological processes complete the sequestration.

If deep-sea carbon sinks were to weaken due to these climate-induced changes, CO₂ would accumulate faster in the atmosphere, making the 1.5 target significantly more difficult to achieve. Therefore, the deep ocean’s capacity determines the long-term fate of CO₂ and the ultimate success of the Paris Agreement’s targets.

Acting without a precautionary approach and failing to incorporate Indigenous values could further damage marine ecosystems and increase inequalities. In addition, failing to establish appropriate protocols for research ethics, project implementation and scientific assessments could result in negative outcomes in terms of CO₂ sequestration.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Juliano Palacios Abrantes, University of British Columbia and Narissa Bax, University of Tasmania

The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.