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Realising the Climate Benefits of the High Seas Treaty

Isabella Notarpietro | Climate Change Fellow

Image credit: Matt Hardy via Unsplash

On the 5th of March, following almost two decades of international discussions, nearly 200 countries agreed to the draft text of the first UN High Seas Treaty. The treaty was widely heralded as a ‘historic win for the planet’ as it establishes a global governance approach to sustainably managing and conserving the two-thirds of the world’s oceans which fall beyond national jurisdiction known as the ‘high seas’.

Critically, the treaty also has the potential to be a win for climate action. For a long time, the high seas have been overlooked as a tool for climate mitigation and adaptation due to their limited governability. With the world’s oceans storing 90 per cent of the world’s excess heat and absorbing over 25 per cent of the world’s carbon emissions, the new agreement offers an opportunity to shift this dynamic and reframe the high seas critical for addressing the climate crisis. Realising this opportunity requires forefronting climate mitigation and adaptation in the implementation of the new treaty and better integrating the high seas within regional and international climate policy approaches.

The Ocean-Climate Nexus

The planet’s climate and oceans are closely interlinked, a dynamic known as the ‘ocean-climate nexus’. Recognition of this nexus has increasingly filtered down into climate policy approaches. ‘Blue carbon’ initiatives which focus on carbon capture in coastal and oceanic ecosystems were a focus of both COP25 in 2019 and COP26 in 2021, the latter of which hosted an Ocean Action Day and advanced the message that ‘ocean action is climate action’. This focus was furthered by the UNFCCC’s dedicated Ocean and Climate Change Dialogue 2022.

Following these conferences, a record number of coastal nations now have at least one ocean-related element in their Nationally Determined Contribution submissions which outline strategies countries will adopt to reduce their emissions. Regional initiatives are also emerging; for example, Amazon and Conservation International have established the International Blue Carbon Institute to advance climate mitigation through the ‘restoration and protection of coastal blue carbon ecosystems in Southeast Asia and beyond.’ Meanwhile, the recently created multi-sector Sea Change Impact Financing Facility (SCIFF) aims to close the ocean investment deficit by channelling at least USD$1 billion of private finance into coastal and ocean climate initiatives by 2030.

By and large, the focus of these blue carbon policy approaches has been on coastal ecosystems. Meanwhile, the high seas have largely been overlooked due to the difficulty in governing and implementing initiatives in areas which fall beyond national jurisdiction. The new treaty offers a unique opportunity to change this dynamic and start employing the high seas as a tool to combat the climate crisis.

Potential Climate Benefits of the New Treaty

The recently agreed-upon treaty establishes a governance framework for the high seas across four key focus areas, including the establishment of large-scale marine protected areas (MPAs) in which human activities are heavily limited to protect marine biodiversity. With just over one per cent of the high seas currently protected, expanding high seas MPAs will yield significant climate mitigation and adaptation benefits if appropriately designed, implemented and managed.

Concerning mitigation, MPAs can enhance biological carbon capture and sequestration. A 2018 study identified nine mechanisms by which marine vertebrates capture and sequester carbon, the majority of which only occur in the high seas. These include the ‘whale pump’, a mechanism by which whales’ ‘buoyant, nutrient-rich faecal plumes’ float to the ocean surface and stimulate the growth of phytoplankton, a type of marine plant which captures carbon dioxide and converts it to oxygen. Further, when whales (and other large marine vertebrates) die, they sink to the sea floor and bring with them a lifetime’s worth of carbon which is then sequestered in marine sediment. To realise these potential mitigation benefits, the selection and design of the MPAs should aim to maximise carbon sequestration opportunities.

The treaty could also be used to prevent the release of carbon already stored in the ocean. The top one meter of the seafloor sediment stores more than twice the carbon of terrestrial soil. Disturbance of this sediment through activities such as bottom trawling and deep sea mining (a practice which could be ‘just around the corner’), can release this stored carbon into the ocean and atmosphere. Those implementing the new treaty must thus focus on protecting the seabeds—and carbon stored within—in addition to broader marine biodiversity.

Furthermore, the treaty could advance climate adaptation. One study found that 14 of the 16 climate benefits produced by MPAs were related to adaptation. For example, the enhanced biodiversity and reproductive capacity of marine species in MPAs resulted in increased resilience and adaptive capacity to climate change. Local communities can also benefit, with MPAs increasing fish stocks in nearby areas and thereby increasing food security for people dependent on seafood (of which there are more than three billion). Realisation of these adaptation benefits should be an explicit aim in the treaty’s implementation and management.

Importantly, not all social impacts of the MPAs are positive. The creation of MPAs can threaten the rights of Indigenous Peoples and Local Communities (IPLCs) by limiting access to and traditional usage of marine areas and delegitimising Indigenous knowledges and management practices. As shown by Australia’s Marine Indigenous Protected Areas scheme, however, if MPAs are designed appropriately to enable Indigenous-led management, these areas deliver significant biodiversity and sociocultural benefits.

The Oceans Ahead

Ratification of the treaty is not expected to occur before 2025 and implementation will only take place after that. Despite this long lead-time, some actions can—and should—be taken now. For example, policymakers should start strategising now on how the design, implementation, and management of the treaty can be tuned to maximise the potential climate adaptation and mitigation benefits. Anticipating the increased governability that the new treaty brings forth, the high seas should similarly start being integrated more explicitly into regional and international climate policy approaches. With time rapidly running out to address the climate crisis, we need as many weapons in our arsenal as possible – even whale poo.

Isabella Notarpietro is the Climate Change Fellow for Young Australians in International Affairs.


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