During the international climate negotiations in 2015, Parties to the United Nations Framework Convention on Climate Change (UNFCCC) finalised the Paris Agreement with the ambition of limiting global warming to ‘well below 2°C, preferably to 1.5°C’ (UNFCCC, 2015 - Art. 2(a)). Scientific articles on a wide range of geographical regions, ecosystems, and economic sectors reiterate the imperative of limiting warming to 1.5°C for a thriving planet, especially for marine, coastal and island ecosystems and communities (King et al., 2017; Giardino et al., 2018; McWhorter et al., 2022). The Intergovernmental Panel on Climate Change (IPCC) 2018 Special Report on “Global Warming of 1.5°C”, based on the assessment of 6,000 peer-reviewed publications, put forward emissions pathways consistent with global ambitions of limiting global warming to 1.5°C above pre-industrial levels (IPCC, 2018). All proposed pathways indicate that a global transition towards carbon neutrality is pertinent by 2050, but that residual greenhouse gas emissions from hard-to-abate activities would need to be counterbalanced (IPCC, 2022). Carbon dioxide removal (CDR) from the atmosphere as additional element in the global strategy towards reaching carbon neutrality by mid-century and ultimately limiting global warming, especially to 1.5°C, has been put forward by many studies, as well as the IPCC, for achieving global climate ambition agreed upon in the Paris Agreement (IPCC, 2022). The ocean’s significant role in the earth’s climate system, having sequestered 26% of total CO₂ emissions in the last decade (Friedlingstein et al., 2022), indicates a promising potential for such approaches.

Human interventions have been suggested for the large-scale reduction of atmospheric CO₂ levels in the near-term, to offset emissions from sources that will likely not achieve carbon-neutrality by mid-century and to sustain these efforts for the long-term (IPCC, 2022). Additional CO₂ sequestered from the atmosphere and stored long-term via CDR has the opposite effect to producing emissions, and can be described as achieving ‘negative emissions’ (IPCC, 2018). So-called ‘negative emissions technologies’ (NETs) can broadly be defined as human interventions in nature that remove and store greenhouse gases from the atmosphere with the aim of climate change mitigation. Scientists and private stakeholders have proposed a wide range of technologies that intervene in the ocean as part of the global carbon cycle to increase the ocean’s carbon sequestration potential and storage capacity (Minx et al., 2018; GESAMP, 2019). Approaches include chemical enhancement of carbon storing properties of ocean water (e.g., ocean alkalinisation), a shift in the water column to increase uptake of carbon (e.g., artificial up- and downwelling), or the conservation and restoration of coastal and marine ecosystems with carbon storing properties (e.g., mangroves). These activities intentionally induce a change in the ocean’s biogeochemical and physical condition, or in marine ecosystems, for the purpose of higher carbon uptake and storage.

In comparison to terrestrial NETs, such as bioenergy with carbon capture and storage (BECCS), ocean-based interventions are subject to the interconnectedness of the marine environment, and of the ocean and human society, and consequentially demand international coordination in governance (Boucher et al., 2014; Minx et al., 2018). In addition to mitigating climate change, a change in the ocean’s condition due to ONET deployment may alter the marine environment to an extent where ecosystem service provision within and across jurisdictional boundaries is compromised (GESAMP, 2019). Governance of ONETs must consider the trade-offs between climate mitigation and impaired ecosystem services when assessing the modalities of allowing or restricting such technologies. The fragmented global governance framework in place creates additional challenges for a streamlined approach to governance of emerging ocean uses that potentially affect multiple areas of international cooperation (Biermann et al., 2009; Boyes and Elliott, 2014; Haas et al., 2021). Complexity within the global ocean governance framework is increased by the high uncertainties and many unknowns related to ocean and climate change (Payne et al., 2016), and related to the response of the marine ecosystem to many of such technological interventions (Renforth and Henderson, 2017).

This paper presents a review of direct, implicit and indirect linkages between eight selected ONETs and international environmental agreements (IEAs) including their underlying policy goals for the ocean, and ultimately outlines a global governance framework surrounding ONETs. The review builds on an analysis of potential direct and indirect, intentional and unintentional impacts of eight ONETs on the marine environment and links these to the regulations and policy goals of relevant international environmental agreements of the current ocean governance. It highlights main challenges for the comprehensive governance of ONETs and identifies synergistic opportunities for future governance. Building on a first-order assessment of interactions of ONETs with the ocean, and of potential effects of ONETs deployment on ocean condition and ecosystem service (ES) provision, the type and directionality of linkages between ONETs and relevant IEAs is investigated to identify and map the existing governance framework relevant for a comprehensive approach to regulating and managing ONET deployment. Drawing from recent publications that explore the challenges of ocean governance in light of rapidly increasing human uses of the ocean and the deteriorating condition of the marine environment (Brodie Rudolph et al., 2020; Singh and Ort, 2020; Spalding and de Ycaza, 2020; Stephenson et al., 2021), a broader perspective of (global) ocean governance is adopted in this study. This broader perspective attempts to bring together legal aspects of regulating human activities in the ocean for environmental protection and conservation (Singh and Jaeckel, 2018; Singh and Ort, 2020) with an understanding of the concept of environmental governance as it has developed in the social and political sciences. Pattberg and Widerberg (2015) describe global environmental governance as the system of institutions, actors, processes and governing instruments required to address environmental issues. For the purpose of this study, focus is placed on IEAs as governing instruments and core components of the governance system while widening the scope to include agreements beyond the direct and explicit regulation. Ostrom’s Institutional Analysis and Development (IAD) Framework (Ostrom, 1999; McGinnis, 2011; Ostrom, 2011; McGinnis and Ostrom, 2014) has been instrumental in guiding the study towards such a broader understanding of governance in the context of ONETs and the quest for comprehensive “governance” of ONET deployment, albeit without applying the IAD framework strictly for the assessments conducted.

The research presented here considers eight ocean-based negative emissions technologies (ONETs), pre-selected as a study base by the EU-funded Horizon 2020 project OceanNETs ¹ which the research presented here is part of. Negative emissions technologies are considered ‘ocean-based’ in that their deployment interacts with one or more components of the ocean, such as the seafloor, ocean water or marine biomass (Boucher et al., 2014). These ONETs are a non-exhaustive representation of recent and emerging technological and scientific studies within the field (Fuss et al., 2018; Gattuso et al., 2018; Keller, 2018; GESAMP, 2019). The selected ONETs range in their status towards deployment from theoretical studies (artificial downwelling), to lab-based (direct electrochemical CO₂ removal from seawater; terrestrial biomass dumping) and mesocosm experimentation (ocean alkalinisation), field testing (artificial upwelling; ocean fertilisation) and fully operational (blue carbon ecosystems). The presented research is limited to the assessment of ONETs’ interactions with the ocean (including coastal zones) during deployment whereby freshwater and terrestrial impacts, as well as related governance frameworks, are beyond the scope of this study. Impacts of technologies on the marine environment during other lifecycle phases, such as initial implementation (e.g., via shipping of materials, installation of infrastructure) are acknowledged in this study, but as the scientific literature currently provides limited information in this regard, the focus is on impacts linked to the operation of the technologies.

The identification and analysis of the governance framework surrounding selected ONETs encompassed four steps (see Figure 1 ). As a first step, a knowledge base was created for each of the eight technologies and captured in overview tables. A short online questionnaire was developed to gather expert knowledge on key aspects of ONET deployment that are relevant to the regulation and governance of ONETs governance. The questionnaire was administered with members from the OceanNETs project consortium and comprised of six questions pertaining to 1) the interaction between the eight selected ONETs and the ocean, 2) potential area and scale of deployment, 3) engaged maritime zone (coastal waters, exclusive economic zone, high seas) and parts of the ocean and water column (deep sea, surface waters etc.), 4) possible co-benefits, 5) possible environmental or socio-economic concerns, and 6) relevant factors to consider for ocean governance. The information gathered via the questionnaire served as starting point for an extensive literature review, which was carried out for each of the technologies. Both the GESAMP (2019) report of Working Group 41 “High Level Review of a wide Range of proposed Marine Geoengineering Techniques” and the National Academies of Sciences, Engineering, and Medicine (2022) report “A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration” served as primary resources for the literature review. Variation in availability of scientific publications between the eight ONETs affected the review, with a more extensive literature base available for some, e.g., ocean alkalinisation and fertilisation, and limited available scientific knowledge for technologies in early research stages, e.g., artificial downwelling (Fuss et al., 2018; Minx et al., 2018; Nemet et al., 2018; GESAMP, 2019).

A qualitative description of the impact of each ONET on the ocean’s condition and its ES was carried out next (step 2). Building on the data compiled with the initial questionnaire and literature review in step 1, the potential impacts of the selected ONETs on the ocean were mapped along Essential Ocean Variables (EOVs), as defined for the Global Ocean Observing System to provide a structured framework for coordinating measurements and describing the ocean condition (Lindstrom et al., 2012; Miloslavich et al., 2018; Tanhua et al., 2019; Global Ocean Observing System, 2021; Satterthwaite et al., 2021). EOVs comprise a list of physical, biochemical and biological/ecosystem variables (Global Ocean Observing System, 2021). For this first-order mapping, EOVs were employed as they allow to structure possible physical, chemical, and biological/ecosystem changes in ocean condition induced by ONETs. The mapping exercise produced a qualitative description of each ONET’s effects on the EOVs. Impacts were differentiated as i) direct intentional impact on the ocean’s condition for higher carbon uptake and ii) potential direct unintentional impacts, and further grouped by (potential) impacts on the ocean’s biochemical, physical, and biological/ecosystem condition, e.g., an unintentional release of trace metals into seawater via ocean alkalinization (see Tables S1 to S8 , Annex I, Supplementary Material ). The impact assessment of “blue carbon ecosystems” was limited to coastal ecosystems, specifically to mangroves, salt marshes and seagrass meadows.

Based on these findings, and to further determine the potential indirect impact of ONETs on the environment and society, a second literature review was conducted on potential impact of ONETs on coastal and marine ES. For this purpose, the electronic scientific research database Science Direct was consulted using a key word search, combining the identified direct effects on the ocean (e.g., “coral reef recovery”) with the key words “ecosystem service*”, “marine”, “coast*” and “ocean”. For this mapping exercise, the Common International Classification of Ecosystem Services, Version 5.1 (Haines-Young and Potschin, 2018) was utilised to select relevant coastal and marine ES and describe the potential impacts of ONETs on the supply of these, grouped into provisioning services, regulation and maintenance services, and cultural services. These findings were determined as either indirect intentional impact (i.e., climate regulation) or potential indirect unintentional impact (e.g., enhancing or implicating food provision). The tables in Annex I of the Supplementary Material summarize the results of this qualitative first-order mapping of direct and indirect intentional and potential unintentional impacts of the assessed ONETS on ocean condition and ES. Table 1 provides an overview of the scheme developed for classifying the (potential) impacts.

In step 3, an identification of the governance framework relevant to ONETs was carried out. Results from step 2 determined that all ONETs may impact the ocean’s condition in a highly complex and transboundary manner if deployed, depending on scale and characteristics. The international environmental governance regime would function as overarching governance arena, comprised of legal frameworks and norms as well as the institutional arrangements and procedures in place to implement the goals set out in the individual frameworks. Results of the impact assessment determined that ONETs would further likely indirectly impact a wide range of global policy goals, such as protection of cultural heritage or food security. A total of 452 multilateral agreements, provided by the International Environmental Agreements Database Project (Mitchell, 2002-2022), were screened for relevance to the direct and indirect governance of ONETs. International agreements were selected for further analysis if identified as (explicitly, implicitly or indirectly) regulating or governing, or being relevant for the governance of potential impacts of ONETs on the ocean. Regional agreements (e.g., Antarctic Treaty System) were excluded to limit the scope of the study. Eight international frameworks were identified to form the governance framework for ONETs (see Table 2 ).

Step 4, the analysis of selected governance frameworks, involved a review of the legislative text of each agreement including amendments, decisions, resolutions or supplementary documents. Table 3 provides an overview of the scheme developed for classifying and describing the different frameworks in terms of their relation to ONETs, i.e., whether they provide direct regulation or explicit guidelines for dealing with ONETs, implicitly establish a framework for governing ONETs, or comprise an indirect governance framework by addressing indirect and unintentional effects of ONETs on the marine environment. First it was determined if texts explicitly govern, i.e., regulate or in an explicit and direct way address, either geoengineering in the ocean or a specific ONET (e.g., Resolution LC-LP.1, 2008, on the Regulation of Ocean Fertilization) framed as ‘direct and explicit governance’ of ONETs. Next, it was determined which frameworks govern the direct impacts of ONETs on ocean condition (i.e., United Nations Convention on the Law of the Sea, UNCLOS; Convention on Biological Diversity, CBD), as well as the indirect intentional impact of ONETs on the ocean for regulating climate change (i.e., UNFCCC), framed as ‘direct implicit governance’ (see Table 2 and Figure 2 ). Finally, the identified international agreements were analysed in terms of whether they address governance of the potential indirect, unintentional impact of ONETs on the marine environment, via possible impacts on marine and coastal ES (e.g., UN Fish Stocks Agreement).

ONETs have been proposed as human response to climate change, to enhance uptake of atmospheric CO₂ in the ocean and mitigate climate-induced pressures on the planet, including e.g., ocean acidification (Harvey, 2008; Hartmann et al., 2013; Taylor et al., 2016). Future international climate change policy based on IPCC reports is likely set to rely on the inclusion of ONETs as part of the portfolio to achieve net zero emission targets (IPCC, 2022), though the degree to which CDR will be a necessary component to reach global emission reductions targets is still being debated (Buck et al., 2023; Lund et al., 2023). The assumptions made by the IPCC have generated scientific and economic interest in the topic, which in turn may promote the streamlining of ocean-based negative emissions into national climate mitigation strategies (Boettcher et al., 2021). The results presented in this article emphasise the need for inclusion of the ocean environment in CDR decision-making together with potential interconnected impacts to humanity. The presented review of eight ONETs highlights the possible range of biogeochemical, physical and ecosystem changes they could cause to the ocean. A variety of co-benefits and potential negative impacts on ES, as well as persisting uncertainties and unknowns, has been identified and emphasises the complexity of the challenge that ONETs pose for comprehensive ocean governance.

Previous studies have detailed the initial international policy response to ocean fertilisation experiments, and later marine geoengineering in general, and have reflected that ONET deployment will place new demands on the international law and governance system (Galaz, 2012; Williamson et al., 2012; Bodle et al., 2014; Magnan et al., 2016; Gattuso et al., 2018; McGee et al., 2018; Boettcher et al., 2021). This paper builds on this research as it reflects on how ONETs are situated within the broader global ocean governance framework when considering the technologies’ potential intended and unintended impacts on the coastal and marine environment, as well as linked ES. The results of this study suggest a comprehensive approach to governing marine CDR that considers both co-benefits and trade-offs between climate and ocean protection as well as other policy goals. An ocean-centric perspective on ONET governance as additional maritime activity rather than regulation of potential environmental harm, as it is currently governed under the LC/LP, offers a more holistic entry-point to the topic, putting potential trade-offs and synergies within the ocean realm (and beyond) forward for consideration in addition to significant climate mitigation benefits, rather than directly compromising between climate action and other goals of the international community. This approach also reflects propositions made by Dooley et al. (2021) to navigate decision-making based on the impacts of CDR activities on the environment rather than primarily as a contribution to climate mitigation. Careful consideration of the range of potential impacts of ONETs, in addition to the intended climate effects, will allow decision-makers to navigate the pathway towards potential future deployment of the technologies in a social-ecological system-based manner that is cognisant of the overall complexity.

The LC/LP, administered by the International Maritime Organisation (IMO) as a specialised agency of the United Nations, is the explicit regulatory instrument for ocean fertilisation and other future endeavours into marine geoengineering. The regulatory approach includes a detailed “Assessment Framework for Scientific Research involving Ocean Fertilisation” that demands careful inspection of proposals for scientific research for e.g., impacts on the environment. A case-by-case review alone of proposed ONET activity may, however, be unfit for purpose considering the outlined demands for comprehensive approaches. Recognising the interaction of a single ONET with the ocean, though a necessary assessment, will not provide an adequate knowledge base for comprehensive decision-making. Effective (and large-scale) ocean-based CDR for limiting global warming is expected to involve a portfolio of ONETs, rather than following a single-technology approach (Minx et al., 2018). The interdependent nature of the ocean (and climate) system with and between technologies therefore poses an overarching challenge within which ONET governance must operate. A comprehensive assessment framework for ONETs would need to consider the sum of all parts, i.e., encompass cumulative direct and indirect impacts of each added ONET activity to the ocean system, and within potential limitations in availability of ocean data (Moltmann et al., 2019), which poses added challenges for decision-making. A comprehensive governance framework accordingly requires, besides the integration of relevant frameworks and processes (see Figure 2 for a proposed wider framework), integration of strategic foresight mechanisms to bridge gaps resulting from extensive uncertainties and unknowns linked to ONET deployment in a changing ocean and climate.

Furthermore, ONET governance can be deemed decision-making under “deep uncertainty” (Constantino and Weber, 2021), and can lead to policy paralysis where inaction can erroneously appear like the leading way forward (Polasky et al., 2020). While risk characterisation mandated by the LC Assessment Framework includes an assessment of uncertainty associated with proposed activities, an integrated foresight-oriented approach of anticipatory governance may be better suited to regulating ONET activities in a holistic manner, especially as the future state of the world and the ocean environment itself holds many uncertainties. Governance and decision making with regards to global climate change mitigation is simultaneously fuelled by an urgency to act (Orlove et al., 2020), which may impact effective ONET governance as significant components of “good” governance, such as general transparency and early stakeholder engagement, may be skipped as CDR becomes more relevant to the global climate change strategy (Moon et al., 2017).

The global ocean governance framework is set up in a fragmented sectoral regime of institutional frameworks that is often criticised for being in itself unfit for purpose as it does not match well with the spatial and temporal specificities of the ocean as a fluid, interconnected realm (Young et al., 2007; Mahon et al., 2015; Wright et al., 2016; Grip, 2017; Watson-Wright and Luis Valdés, 2019). These issues also come to a fore in the context of marine CDR and possible future and large-scale deployment of ONETs. For instance, the Parties of the CBD have restated the Resolution made under the LC/LP to limit ocean fertilisation activities to those of a research character until associated risks are appropriately assessed and considered. Further, the CBD has positioned itself against geoengineering activities with potential adverse effects to biodiversity in general (UNEP, 2010b). The dual approach within the current global ocean governance framework, directly regulating ocean fertilisation and potentially further marine CDR technologies in the sense of avoiding environmental impacts from a specific source (LC/LP), as well as treating ONETs as potential threat to conservation of marine living resources (CBD), indicates the complexities of ONET governance within a fragmented framework. These two frameworks have different mandates (LC/LP: prevention of pollution; CBD: conservation), geographic scope (LC/LP: the global ocean; CBD: for components of biological diversity, areas under national jurisdiction; for processes and activities, both within and beyond national jurisdiction), differing parties to their convention, a different level of binding force for relevant decisions and resolutions (LC/LP: binding, CBD: non-binding), and their processes are not integrated. Besides such duplicity of efforts, one of several prevailing issues of current ocean governance (Singh and Ort, 2020), there are also persisting gaps in the direct governance framework that require attention. Emerging ONETs that alter ocean condition for higher carbon uptake by means other than dumping of substances, e.g., artificial upwelling, are not (yet) explicitly considered within LC/LP. Such emerging technologies may thus not be adequately addressed by the existing governance structures, or not addressed at all, unless they are considered in the Annex of the 2013 Amendment to the London Protocol which is yet to be further detailed - and yet to enter into force.

The United Nations’ 2030 Agenda for Sustainable Development (United Nations, 2015) commits the global community to transform current trajectories in multiple topical areas, including climate action (SDG 13) and sustainable use and conservation of the ocean (SDG 14). The 2030 Agenda now is at the mid-point of its implementation and, as the High-Level Political Forum on Sustainable Development (HLPF) stressed when calling for the 2023 SDG Summit, “a new phase of accelerated progress towards the SDGs” appears indispensable to achieve the goals set (ECOSOC, 2023). In the preamble of the ambitious resolution the UN General Assembly adopted in 2015 (United Nations, 2015), the global community is reminded that the 17 sustainable development goals (SDGs) and their individual targets form an indivisible and integrated whole that seeks to balance all dimensions of sustainable development. ONETs offer a promising pathway towards accelerated progress for climate change mitigation, a field in which necessary transformative action on the national level is still greatly lacking. But it must not be forgotten that none of the goals can be achieved in isolation, which accounts for the climate goals SDG 13 as well as for the ocean goal SDG 14 (Griggs et al., 2017). And, furthermore, no goal should be compromised for another one, unless the global community makes a deliberate and well-informed decision in such a direction. Healthy oceans are linked to food security and livelihoods, among other things (Schmidt et al., 2017), and although climate change has negative effects on ocean “health”, actions to combat climate change should not compromise other objectives, including those that concern global ocean governance, such as the protection and preservation of the marine environment. The 2030 Agenda, as aspirational as it is with its overarching goal to leave no one behind, demands consideration of the interests and needs of humankind as a whole and in an equitable manner. Steering ONET governance forward under the principles set by the 2030 Agenda requires a balanced consideration of all of humanity’s goals and decision-making on the basis of synergies rather than trade-offs. An added difficulty is provided as global ocean and climate governance frameworks so far fail to effectively integrate the overlaps between each other’s regimes (Gallo et al., 2017; Spalding and de Ycaza, 2020), even though the interlinkages between the ocean and climate system are fundamental both in tackling climate change as well as ocean degradation. Further, international ocean governance is set up in a patchwork approach and objectives, whether seemingly opposing (e.g., blue growth and biodiversity conservation) or working in the same direction, are sometimes regulated by separate agreements and entities that fail to integrate the other’s provisions to governance (Stephenson et al., 2021). This disconnection is reflected in the indirect governance framework developed for ONETs (see Figure 2 ) as it is made up of sectoral as well as conservation regulation. Strengthening of policy coherence and integration within the identified ONET governance framework for climate mitigation, ocean preservation and other linked policy goals may pre-emptively alleviate pressure nodes in future decision-making regarding ONET deployment.

In contrast, blue carbon as a nature-based solution, which in the past has been considered as a comparatively low-risk or “low-regret” option for marine CDR (Gattuso et al., 2021), has successfully mainstreamed the ocean’s ability to store additional carbon into global climate policy (e.g., REDD+). The identified governance framework for ONETs is positioned comparatively favourable towards restoration and management of coastal blue carbon ecosystems. Blue carbon is sometimes excluded from the negative emissions technologies discourse altogether and rather discussed as nature-based solution of high feasibility (Howard, 2016), with a wide range of local to global co-benefits linked to implementation (Hilmi et al., 2021). Albeit this universal understanding has recently been challenged (Williamson and Gattuso, 2022), and the current governance framework may not be nuanced enough to appropriately identify potential negative impacts of activities related to blue carbon.

In addition to lacking comprehensiveness, the current direct governance framework surrounding ONETs can be described as largely reactive and lacking foresight. It would be beneficial to determine how best to approach ONET governance in a manner in which trade-offs are minimised and benefits are encouraged as well as distributed fairly across the globe, and in anticipation of future challenges. Emerging technologies such as ONETs require consideration as an additional human use of an already exhausted ocean space (Halpern et al., 2019), for which protective regulation has failed on multiple scales since the adoption of UNCLOS (Zondervan et al., 2013). Furthermore, the challenges surrounding ONETs, and the identified gaps and open questions of current regulation and governance, call for a comprehensive approach to governing the deployment of such technologies in the ocean. Customary international law in this context offers very relevant elements (GESAMP, 2019), including through principles such as such as the precautionary approach and the no harm principle. Equity and fairness are rightly reflected upon critically in contemporary discussions on ocean governance (Bennett, 2018; Bennett, 2022), and with the emerging topic of ONETs lies the opportunity to integrate such knowledge advances. Codes of conduct have been put forward to give guidance on how to best govern CDR, such as the Oxford Principles for geoengineering (Rayner et al., 2013) that include public participation and transparency as key pillars for future governance. A comprehensive approach therefore would not only encompass a wider framework of direct, implicit and indirect governance elements ( Figure 2 ), key principles of ocean governance and codes of conduct for marine geoengineering, but also take up principles of “good” governance such as coherence, equity and inclusiveness (CEC, 2001; Chang, 2010) in order to establish a meaningful and widely acceptable framework for navigating the future deployment of ONETs. The draft agreement on the conservation of marine biodiversity in areas beyond national jurisdiction (United Nations, 2023), negotiated under the United Nations Convention the Law of the Sea, may be critical towards closing gaps in ocean governance of the high seas and further addressing concepts such as benefit sharing and the common heritage for humankind in the ocean realm. Pending final editing, signing and ratification, the new treaty could be supportive of action that helps reduce climate change impacts on marine ecosystems. The exact standards, guidelines, and processes of the treaty, including for environmental impact assessments and related UN processes, including LC/LP, are still to be further detailed.

The assessment of interactions of ONETS with the marine environment and subsequent analysis of related international environmental agreements, as presented here, rendered a unique perspective on the direct, implicit and indirect governance framework that is pertinent for ONETs and potential future deployment at global scales. A closer look at current regulation and governance of ocean-based CDR through the lens of ocean governance reveals a number of challenges and open questions that must be addressed before the perceived, advocated or mandated urgency to act and include (marine) CDR in the global climate mitigation strategy, or interests of individual actors and stakeholders, become the driving force. The assessment presented here points to the need for integration and coherence between the frameworks currently addressing ONETs, whether directly, implicitly or indirectly, and to the need for an overall comprehensive governance approach. There are many examples where the technological enhancement of activities that engage the ocean for society’s benefits has in fact led to negative outcomes for the complex ecosystem, such as offshore oil and gas rigs and bottom-trawlers that have disrupted the ocean floor for economic gain (Zacharias, 2014). While strengthening efforts towards limiting global warming is central for the sustainable development of the planet (Fuso Nerini et al., 2019), global governance of ONETs must appropriately consider the wide range of impacts on the ocean’s condition and linked marine and coastal ES. This includes nuanced assessment of widely endorsed blue carbon ecosystems. On the other hand, ONETs as a solution to climate change may potentially equally benefit the marine environment, as it would society in the long term. A case-by-case assessment of ONETs’ impacts on the ocean environment, which would be the practice under current direct regulation through LC/LP, may not be appropriate for good decision-making. A robust assessment of potential accumulative unintended impacts of ONETs on the ocean, and of potential long-term effects, must be streamlined into governance and decision-making processes.

Nonetheless, as with trade-offs related to the absence of climate mitigation measures or mitigation limited to emissions reductions, the risks associated with deployment of ocean-based NETs must be assessed and weighed in accordance with their trade-offs and benefits to humankind, the marine environment, and other goals set out in the 2030 Agenda for Sustainable Development such as food security (SDG 1) and conservation and sustainable use of life below water (SDG 14). Known impacts on ocean condition and related ES have been presented in this study and reveal a range of potential trade-offs that the governance framework surrounding ONETs needs to recognise and consider to potentially decide in favour of global climate ambitions over other policy goals. A robust and foresight-oriented governance framework that aims for integration between the different frameworks in place, or sets up a new, overarching structure that allows for rigorous oversight and integration of a suite of principles aligned with “good” governance seems mandatory. Ocean governance in general, but also existing (direct) ONET regulation, tend to be reactive. The findings of this assessment, though, strongly suggest that decision-making needs to get ahead of the issue instead of lagging behind these emerging technologies in order to ensure best possible outcomes for people and planet. The deep uncertainty that surrounds ONETs, their intended and unintended impacts on the marine environment, and their real-world contribution to combatting climate change, should be cause for precaution - but not for paralysis in policy making, as the urgency of the climate crisis demands decision-making within appropriate time frames. Still, robust and “good” governance approaches should lead the way and future decision-making should not be rushed in favour of quick fixes. Climate action via long-term emission reductions has a tendency to be very slow when economically unappealing.

Global ocean governance presents many complexities and is further challenged by the climate issue. Spalding and de Ycaza, 2020) like many other authors critically emphasise that there is a general lack of comprehensiveness in ocean governance in light of the challenges the ocean, and with it humanity, is facing. New emerging technologies such as the set of ONETs discussed in this paper introduce further challenges and a possibly quickly moving “target” which policy and decision-making, but also public deliberation, must keep up with – and, better yet, get ahead of the debate and technological developments. With regards to comprehensive governance of ONETs, it may be required to identify pathways “through” the prescribed ocean governance framework rather than attempting to eliminate the weaknesses of the system. Research is needed not only into technical feasibility or cost-effectiveness of ONETs, but also into what “good” governance of ONETs could or should look like – including from an ocean and environmental perspective. Therefore, the identified ONET governance framework not only reiterates current challenges in ocean governance, but also represents an opportunity for a synergistic and integrated approach to future governance. Consideration of governance of land-sea interactions of ONETs was beyond the scope of research, as well other aspects such as carbon accounting, but is of course also highly relevant for future research activities towards good governance of ONETs. Concrete elements of comprehensive ONET governance based on the findings presented in this study are subject to follow-up research and can be used as starting point for developing pathways towards future ONET governance on the global to regional level.

The original contributions presented in the study are included in the article/ Supplementary Material . Further inquiries can be directed to the corresponding author.

Ethical review and approval was not required for the study on human participants in accordance with the local legislation and institutional requirements. The research and activities carried out by the researchers as part of the EU funded OceanNETs project comply with ethical principles and relevant national, EU and international legislation, such as the Charter of Fundamental Rights of the European Union and the European Convention on Human Rights.

LR and BN conceptualised the study; LR performed the impact mapping; LR and BN performed the governance framework analysis; LR wrote the manuscript with contributions from BN. All authors contributed to the article and approved the submitted version.