Laying waste to the deep: parallel narratives of marine carbon dioxide removal and deep-seabed mining

The deep ocean (below 200 m depth) is facing mounting, and often compounding, anthropogenic impacts including climate change, pollution, and resource extraction¹. Two nascent threats currently motivated by climate change are marine carbon dioxide removal (mCDR) and deep-seabed mining (DSM). mCDR seeks to enhance atmospheric carbon removal and deposition of carbon into the deep ocean in the form of artificially fertilized phytoplankton blooms, macroalgae, crop, and wood waste or direct injection of liquid CO₂². DSM seeks to extract cobalt, nickel, and copper from nodules, crusts, and sulfides on the seafloor to support electric battery production³. Because these enterprises both target the deep ocean, they face similar challenges: the location of operations is remote and challenging to access and study, there is a lack of relevant data, impacts are difficult to estimate and contain, and enforcement of regulation is problematic.

Beyond practical challenges, there are striking similarities between the narratives that are used to motivate and rationalize mCDR and DSM. We outline commonalities in the history, motivations, risk considerations, and equity dimensions of these activities and their underlying narrative traits, showing that while the narratives are similar, proposals for DSM have become increasingly risk-oriented through a widening of perspectives from narrowly framed climate goals to holistic considerations including impacts on marine life and human wellbeing. Based on this comparison, we suggest that the development of narratives surrounding DSM offers valuable insights for contemporary debates about mCDR and the use of the deep ocean as a climate solution, which we argue needs to be similarly broadened and risk-oriented. While plans for mCDR include the entire ocean, we focus on the deep sea as the imagined site for the final disposal of captured carbon.

Deep-seabed mining emerged as a significant narrative in the 1970s⁴. In 1994, the International Seabed Authority (ISA) was established under the United Nations Law of the Sea (UNCLOS) as the body responsible for regulating the prospective industry. To date, the ISA has yet to finalize regulations and no commercial mining has occurred in the deep ocean. Over time, two distinct and opposing narratives have crystallized around DSM. By 2011, proponents such as DeepGreen Metals (now The Metals Company) started using climate change as a reason that mining was not only acceptable but essential to provide minerals for electrification. Meanwhile, since the ISA started to grant exploration contracts in 2001, concerns have grown over environmental risks associated with DSM. These now appear front and center of discussions, including in the development of the international mining code at the ISA. In 2021, a call for a moratorium on mining in international waters was initiated by several island nations. Since then 27 nation-states, alongside numerous inter-governmental and non-profit organizations, indigenous leaders, scientists, corporations, and financial institutions, have indicated support for a precautionary pause, a moratorium, or an outright ban (https://savethehighseas.org/moratorium_2022/).

In contrast, mCDR ideas from their inception were tied to climate change mitigation. Like DSM exploration, which experienced a flurry of activity in the 1970s and then a twenty-year hiatus due to falling metal prices and legal constraints, initial mCDR activities focused on iron fertilization and deep-water CO₂ injection were explored in the 1990s and 2000s and then halted until recently due to scientific concern and policy restrictions^5,6,7,8. With countries committing to the 2015 Paris Agreement goal of limiting warming to 1.5 °C, and the IPCC indicating that this cannot be met without active carbon dioxide removal, proposals for mCDR have diversified and gained new momentum^9,10. Current proposals mostly fail to acknowledge and position themselves in relation to the contested history surrounding ocean iron fertilization and related technologies¹¹; recognizing this history would help to highlight previous apprehensions, assess what may be different in the present, and thus inform current and future debates¹².

DSM has been promoted by industry and the ISA through a narrative based on assumptions about the amount of minerals needed by society, and especially their role in the so-called “green transition”. Communications from The Metals Company, a central actor in promoting commercial DSM, compare the “environmental, social, and economic impacts” of extracting minerals from land versus the seafloor, noting the extensive harm of terrestrial mines and stating that their aim is to provide necessary metals “in a way that inflicts the least impact on the planet and people” and gives “fragile rainforest ecosystems a break” (https://metals.co/)¹³. However, the size of the area that could be impacted by DSM in just the Clarion Clipperton Zone, currently the main target for commercial mining operations, is an order of magnitude larger than all areas impacted by terrestrial mining, and much greater by volume^14,15. Similar differences in the scale of impacts likely apply to CDR on land versus in the ocean, though this has yet to be assessed.

The narrative of necessity used to promote DSM is entirely questionable¹⁶. Predictions of future needs for minerals are highly uncertain. Increasingly, changes in battery technology and recycling are leading to the conclusion that DSM is “neither necessary, economically advantageous, or environmentally advisable”¹⁷. Moreover, to acquire enough minerals to be profitable, DSM would have to operate in vast areas for multiple decades, and would in no way be light-handed in its impacts on deep-sea ecosystems, as sometimes indicated by proponents.

Alongside DSM, mCDR is regaining attention as a similarly alleged necessary intervention for mitigating climate change¹⁸. The CEO of Ocean Visions, a non-profit organization supporting advancement of mCDR, recently stated that “record levels of global warming have put the planet and ocean in such peril that aggressive large-scale measures are essential” and that “it’s not a question of whether we do carbon removal, but rather where we do it”, and further that this perception is informing “a swell of interest” in mCDR¹⁹.

As with DSM, claims of the necessity, feasibility and advantages of mCDR technologies involving the deep ocean are debatable^20,21,22. There is at present no proven technology that would remove carbon from the atmosphere and relocate it to the deep sea with sufficient efficacy to make it relevant as a climate solution²³.

To have any meaningful impact, both DSM and mCDR would need to be deployed on vast scales, which would carry significant risks for deep-ocean ecosystems and may disturb many of their functions that people depend on ²⁴. Dumping large amounts of carbon, whether as liquid CO₂, macroalgae, crop waste, or phytoplankton, would alter geochemical conditions in the deep ocean, modify substrate, and smother life at the seabed²⁵. DSM would damage life on the seafloor and in the water by removal, disruption, smothering by sediment plumes, noise, light, and contamination²⁶. Both DSM- and mCDR-induced changes in water chemistry and marine ecosystems at the seafloor and in the water column would impact natural components of the marine carbon cycle including the biological pump, with likely unknown and unintended consequences for the ocean’s natural absorption, transfer, and storage of carbon.

For both mCDR and DSM, impacts at scale (for exploitation or climate remediation) cannot be fully known without massive large-scale testing, long-term research, and cross-disciplinary assessments (including both natural and social sciences perspectives). The lines between testing, research, and commercial deployment become blurry in such operations. International governance of deep-sea exploitation, including DSM and mCDR, is challenging, contributing to inherent economic, environmental, and social uncertainty^27,28.

While the risks of DSM have over the years become increasingly recognized, leading to the current call for a moratorium or pause, risks associated with mCDR are still forcefully played down or ignored, as seen recently at COP28 in Dubai, where proponents even suggested that there is a need to address uncertainty and fear of these technologies in order to create “technical, economic, social, and political enabling conditions” for pursuing mCDR, and not defer due to scientific uncertainties²⁹. While the ISA provides a forum for assessing, monitoring, and identifying the risks of DSM, there is currently no equivalent governance body that would oversee all aspects of mCDR. The London Convention and Protocol govern some ocean inputs associated with mCDR and the new Biodiversity Beyond National Jurisdiction Agreement could advise on environmental impacts; however both presently suffer from limited ratification of the relevant annex or treaty, respectively (6 parties have ratified Annex 4 of the London Protocol while 8 parties have ratified the newly-signed BBNJ Agreement), and neither has entered into force.

Initial interest in DSM from developing countries stemmed in part from potential income via the “common heritage” principle assigned by UNCLOS to minerals in the Area (the seabed in international waters). Recent suggestions for how that principle could be implemented suggest that monetary benefits for humankind would be minimal³⁰. There is also no guarantee that extracted minerals would in fact be used to support decarbonization, as mining companies routinely claim. In the case of mCDR small-scale deployments can be motivated by profits from the sale of carbon credits (that would likely have no real effect on the climate)³¹. Some mCDR startup companies have attempted to interest developing countries in field trials and eventual deployments as contributions to their NDCs and potential sources of income. More lax permitting regulations and financial needs have made such countries attractive for both mCDR and DSM, as evidenced by the initial push for DSM in Papua New Guinea and now Cook Islands, and rapidly progressing plans for testing and commercialization of mCDR in Caribbean, African and South Asian waters (https://map.geoengineeringmonitor.org/)³². This raises issues of equity for both endeavors, with the risk that new forms of “carbon colonialism” replicate patterns of past resource exploitation by colonial powers³³.

The claim that the deep ocean offers a space for more equitable mining or carbon removal operations than terrestrial alternatives is not true; rather the challenges are different³⁴. Impacts from both DSM and mCDR would extend far beyond the immediately impacted ecosystems and into the social realm, where they may exacerbate existing environmental and social inequalities³⁵. Assessments of equity are not well developed in international ocean governance, and though the international seafloor is legally defined as the common heritage of humankind, it remains unclear how this principle could or should be implemented^36,37. The lack of a framework for equitable governance of the deep ocean underlines the need to proceed with any activities that may cause severe or irreversible harm and would operate under conditions of profound uncertainty with great caution³⁸.

The idea of climate change mitigation as an overarching political goal that needs to be reached at all costs and within a certain timeframe has been described as “climate reductionism”, “climatism”, or “climatization”, defined as the reduction of broad social, economic and ecological policies to narrowly framed, often numerical, climate goals^39,40. Focusing on targets such as keeping the increase in global temperature to below 1.5 or 2 °C “creates a dangerous discourse of scarcity” according to which “there is not enough time to reflect, deliberate or experiment”, which may lead to poor decision-making⁴¹. Current narratives of mCDR reflect this rhetoric, suggesting that pursuing mCDR is essential in response to the Paris Agreement and that there is little time to deliberate⁴².

Narrowly defined climate goals and the perception of a limited timeline have also been used to promote DSM. The letter submitted by Nauru to the ISA in 2021 to invoke the so-called 2-year-rule notes the IPCC’s claim that “humans can emit no more than 420 gigatonnes (billion metric tons) of carbon dioxide into the atmosphere by 2050 to retain any hope of limiting global warming to 1.5 °C” as the basis for Nauru’s determination to ensure “that polymetallic nodules are part of the solution to the global transition required to secure a clean renewable energy future” (ISBA/26/C/38, Enclosure, p. 4). The letter further states that historical devastation wrought by colonial mining on their island has given Nauruans “a unique insight into the future of our world if mining on land continues to meet the exponential growth in demand for the base metals that will underpin our transition to a renewable energy”. The solution envisioned is the “responsible collection of polymetallic nodules from the seafloor”.

We find that Nauru’s complex history of resource exploitation, colonialism, and exposure to climate change in fact demonstrates the opposite of climatism, namely that climate impacts are not solely or straightforwardly determined by exact levels of CO₂ in the atmosphere or degrees of warming. Rather, they are the result of complex interactions between natural and social factors that shape societies and their resilience to weather and climate, pointing to how risks and benefits of mCDR and DSM need to be carefully weighed within a broad framework of their potential political, ecological, and economic impacts in order to make decisions that support human wellbeing holistically and long term.

In presentations of mCDR strategies, the deep ocean is routinely depicted schematically as a black, featureless abyss, without acknowledgement that the receiving environments for carbon disposal are biodiverse, heterogeneous, and provide critical ecosystem functions. Up until the 1970s, plans for retrieving minerals from the deep seabed likewise included no recognition of the potential harm caused to species living there. While such impacts now motivate many DSM debates, proposals for mCDR continue to rely on an outdated view of the deep ocean as a place where waste can be dumped far from sight and without consequences.

Research into the risks associated with DSM has informed a counter-narrative to the emergency framing and “climatism” used by proponents of deep-seabed mineral extraction. A similar counter-narrative has yet to receive comparable attention in current debates on the feasibility and safety of mCDR but is very much needed. Consideration of a wide array of risks associated with large-scale mCDR interventions and consequences for marine ecosystems and environments is rapidly becoming essential as business interests outpace science and policy development. Like DSM, mCDR needs to be carefully considered not in relation to narrowly framed numerical climate targets, but within a holistic framework including potential far-reaching impacts on marine life, deep-ocean ecosystems and social equity.