Ocean-Based Solutions Can Help Close the Climate Emissions Gap

Abstract

In the context of mounting climate impacts and growing urgency to meet the Paris Agreement goals, the ocean is now increasingly being recognised not just as a victim of climate change, but as an indispensable part of the solution. Research has demonstrated that readily actionable ocean-based climate solutions can help close the emissions gap (the difference between the greenhouse gas emission reductions needed to limit global warming to 1.5 °C, and projected global emissions considering current national pledges and policies) by providing approximately a third of the mitigation needed to keep the Paris Agreement’s 1.5 °C goal within reach. This mitigation potential (of fully actioning these solutions) is unequally divided across seven key ocean-based action areas (listed in decreasing order of magnitude): phasing out offshore oil and gas; deploying offshore renewable energy infrastructure; decarbonising maritime transport and associated infrastructure; decarbonising ocean and aquatic food value chains; carbon capture and storage; marine and coastal conservation and restoration; and decarbonising coastal tourism. We argue that achieving the full potential of ocean climate solutions will require smart governance, drastically increased financial investment, and international cooperation. Accomplishing this, however, will bring strong co-benefits for biodiversity, food systems, and coastal resilience. The Third United Nations Ocean Conference and 30th United Nations Climate Change Conference of the Parties (COP 30) present rare opportunities to mainstream the ocean into global climate strategies.

1. Introduction

As the climate crisis intensifies, and with a need to drastically reduce global greenhouse gas (GHG) emissions to meet the goals of the Paris Agreement, the ocean is increasingly being recognised not just as a casualty but as a powerful ally in climate mitigation and adaptation [1]. Deployed at scale, climate solutions involving ocean sectors and habitats, such as increasing offshore renewable energy production, restoring blue carbon habitats, and increasing sustainable food production from the ocean, hold significant potential to reduce global GHG emissions, build resilience and support adaptation [2,3,4]. This potential was first brought to the forefront in the late 2010s through the work of, for example, Gattuso et al. [5], Cooley et al. [6], and research commissioned by the High Level Panel for a Sustainable Ocean Economy (Ocean Panel) [2].

Incorporating new data, technologies, and policy developments, subsequent research has highlighted an even larger ocean climate mitigation potential than originally determined [1]. We now know that readily actionable ocean-based climate solutions across seven sectors (

Table 1. Seven ocean-based sectors and associated actionable climate mitigation opportunities.

Ocean-Based Sector	Climate Mitigation Options	Description	Mitigation Potential (Gt CO2e/Year by 2050)	Details
Blue carbon protection and restoration	Restoration of coastal wetlands	Restoration of degraded coastal habitats towards natural state, including mangroves, tidal marshes, seagrasses, and seaweeds.	0.285 [1,8]	Achievable if further losses and degradation of ecosystems is halted, and Global Biodiversity Framework Target 3 is met [9].
	Increasing protection of coastal wetlands	Protection of intact coastal wetland systems, including mangroves, tidal marshes, seagrasses, and seaweeds.
Ocean-based renewable energy generation	Scaling up offshore wind	Installing new fixed and floating offshore wind farms.	3.2–3.6 [1]	Achievable if global offshore wind capacity reaches 2000 GW by 2050, alongside developments in wave and tidal technologies [10,11].
	Scaling-up ocean renewable energy	Installing new equipment to convert and harvest solar energy, and energy carried by ocean waves, tides, salinity, and temperature differences.
Ocean-based transport	Reducing emissions from domestic shipping and marine transport	Reducing emissions from shipping between ports within the same country.	2.0 [1]	Achievable if the IMO Strategy on Reduction of GHG Emissions from Ships is met [12].
	Reducing emissions from international shipping	Reducing emissions from shipping between ports across different countries.
Ocean-based tourism	Reducing emissions associated with cruise tourism	Reducing emissions from tourism where tourists are accommodated on and transported by ships.	0.05–0.1 [1]	Achievable if global ambition mirrors that of the EU’s FuelEU Maritime regulation, mandating shore power from 2030 and advocating for the uptake of alternative fuels [13].
Ocean-based food	Reducing emissions by rebuilding depleted wild fish stocks	Reduction in fuel use intensity to harvest fish and shellfish that results from rebuilding depleted stocks.	1.47 [1]	Achievable with a reduction in fishing effort to optimal levels, and full substitution of animal-based protein for available fish protein sources.
		Avoided emissions if the increased harvest achieved via rebuilding stocks is consumed in place of higher emissions land-based animal products.
	Reducing emissions from aquaculture	Improved feed conversion ratios.		Achieving mitigation potential requires the behaviour change of shifting diet. Health benefits of this shift may be a more persuasive argument for the change than carbon mitigation benefit [14].
		Complete avoidance of deforestation in the supply chains of aquaculture feed ingredients from soy, palm, and other crops as well as in the feeds of poultry and livestock systems providing by-products for aquaculture feed.
		Shifting all energy inputs to farms to be derived from renewable electricity, as opposed to that derived from fossil fuel sources.
	Increasing the share of ocean-based protein in diets	Potential emissions avoided by behavioural shifts away from high emissions land-based proteins and towards lower emissions seafood systems.
Offshore oil and gas	Stopping the expansion of offshore oil and gas extraction alongside a phase-down of current production	Potential emissions avoided via reduction in the production and consumption of offshore oil and gas.	5.3 [1,15]	Achievable if no new offshore oil and gas projects are approved and energy demand is instead met by low-carbon energy sources [15].
Carbon capture and storage	Increasing CO2 storage beneath the seabed	Storage of CO2 below the seabed in geological formations	1.0 [1,2]	Achievable if current and planned projects continue to grow as expected [16].

), if fully actioned, could deliver up to 13.8 Gt CO₂e/year mitigation potential by 2050 [1]. For context, the climate emissions gap—the difference between the greenhouse gas emission reductions required to limit global warming to 1.5 °C and projected emissions considering current national pledges and policies—is 48 Gt CO₂e on a 1.5 °C pathway in 2050, as calculated by the 2024 United Nations Environment Programme emissions gap report [7].

Given the magnitude of this mitigation potential, we argue that ocean climate action is central to meeting global climate goals. However, achieving this potential requires policy integration, significant financial investment, and the inclusion of ocean measures in Nationally Determined Contributions (NDCs).

The Third UN Ocean Conference (UNOC 3) in June 2025, and the 30th United Nations Climate Change Conference of the Parties (COP 30) in November 2025, present rare opportunities to help mainstream the ocean into global climate strategies and place ocean-based climate solutions front and centre.

Here, we summarise the state of knowledge regarding the GHG mitigation potential of the ocean, offer reflections on opportunities for action, challenges, and wider impacts and trade-offs in deploying these ocean climate solutions, and argue why action now is critical if we are to keep the goals of the Paris Agreement within reach.

2. Review of Ocean-Based Climate Mitigation Potential

2.1. Blue Carbon Protection and Restoration

Coastal ecosystems including mangroves, seagrasses, tidal marshes, and kelp forests are powerful carbon sinks [3,17]. Their protection and restoration could mitigate up to 0.285 Gt CO₂e/year by 2050 [1,8] (Table 1). These nature-based solutions also deliver extensive co-benefits for biodiversity, fisheries, tourism, water quality, and coastal resilience [17,18]. However, restoration remains underfunded and under-implemented [17]. Fully actioning this climate solution will require improved mapping, monitoring, and governance, alongside community-led approaches and safeguards to ensure equitable benefit sharing [1,17].

2.2. Ocean-Based Renewable Energy

Offshore wind is currently the best developed and most scalable ocean-based mitigation option [1]. With global pledges now exceeding 2000 GW by 2050 [19], offshore wind could mitigate 3.2–3.6 Gt CO₂e/year [1] (Table 1). Further, offshore wind may present an opportunity for the production of green hydrogen [20]. Other technologies, including wave, tidal, floating solar, and ocean thermal energy, remain in earlier stages but offer further potential [1]. Realising this potential requires investment in infrastructure, supply chains, and marine spatial planning to minimise conflict with other ocean uses [1].

2.3. Ocean-Based Transport

Ocean-based transport, including international and domestic shipping, accounts for around 3% of global GHG emissions [21,22]. The revised IMO GHG Strategy [12] set a target of net-zero emissions by 2050, with interim goals for 2030 and 2040. Full decarbonisation could mitigate up to 2.0 Gt CO₂e/year by 2050 [1] (Table 1). Key levers include operational and logistical efficiencies such as route optimisation considering prevailing weather conditions, retrofitting vessels with sail power and more efficient propellor designs, and transitioning to zero-emission fuels such as ammonia, hydrogen, and methanol [1,22].

2.4. Ocean-Based Tourism

Cruise tourism is highly carbon-intensive, with emissions projected to rise sharply without intervention. Estimates of the mitigation potential of decarbonising cruise tourism range from 0.05 to 0.1 Gt CO₂e/year by 2050 [1] (Table 1). Similar to the decarbonisation of shipping, this can be achieved through energy efficiency measures, use of shore power, and efficient vessel design [1]. In addition to GHGs, cruise ships emit sulphur oxides, nitrogen oxides, and particulate carbon, which harm marine ecosystems and human health [23]. Given the sector’s rapid growth and limited regulation, stronger policy frameworks and consumer awareness are essential [1].

2.5. Ocean-Based Food

Ocean-based food systems, including fisheries and aquaculture, can reduce emissions while providing nutritious, low-carbon protein [24,25,26] (Table 1). Rebuilding wild fish stocks, improving feed conversion ratios, electrifying aquaculture operations, and shifting diets toward sustainable seafood could mitigate up to 1.47 Gt CO₂e/year by 2050 [1]. However, progress towards meeting this potential has been limited to date [1]. Better management of wild fisheries, investment in regenerative aquaculture, and integration of ocean-based food into national climate and nutrition strategies is required.

2.6. Offshore Oil and Gas

Offshore oil and gas production currently accounts for about 30% of global output [27]. Phasing down this sector, starting with the least efficient and highest-emitting operations, could mitigate up to 5.3 Gt CO₂e/year by 2050, making it the single largest ocean climate mitigation solution [1,15] (Table 1). Achieving this requires halting new exploration, reducing subsidies, and ensuring a just transition for workers and communities to alternative livelihoods [1,15,28]. Further, negative emissions technologies cannot act as a substitute for fossil fuel phase-out [1].

2.7. Carbon Capture Storage (CCS) and Marine Carbon Dioxide Removal

Carbon capture and storage below the seabed in geological formations is estimated to have the potential to mitigate up to 1.0 Gt CO₂e/year by 2050 [1,2] (Table 1). Further to this, nascent marine carbon dioxide removal (mCDR) approaches, such as ocean alkalinity enhancement, seaweed cultivation and sinking, and direct ocean removal, could contribute up to 9.0 Gt CO₂e/year by 2050 [1]. However, mCDR technologies are still in the early stages of research and development, and carry significant uncertainties and ecological risks [29]. Developing marine carbon dioxide removal technologies will require a robust, government-backed research agenda, development of national and international governance frameworks, and transparent monitoring, reporting and verification (MRV) approaches to assess their viability and ensure environmental and social responsibility [1,29].

3. Key Actions to Achieve the Potential of the Ocean to Mitigate Climate Change

We highlight and provide examples of ten key actions to support the accelerated implementation of ocean climate solutions (Table 1) within national climate action plans, pathways, and strategies, including the integration and strengthening of ocean-based actions in NDCs, alongside Sustainable Ocean Plans.

1. Translate pledges into action. Prioritise the implementation of existing pledges and targets across all ocean-based sectors to translate their potential into verifiable and measurable action. For example, the Australian Government is acting to achieve the 30 by 30 target of the Global Biodiversity Framework [9] within its national waters. Currently, 22% of Australian waters are fully protected, and during UNOC 3, the Australian Government reaffirmed its intentions to increase this to at least 30% by 2030 [30,31].

2. Foster collaboration and research into emerging solutions. Engage in ambitious, inclusive and collaborative partnerships to address ocean-related challenges and fill the knowledge gaps in emerging ocean-based climate solutions that are not yet ready for implementation. Prioritise research and knowledge-sharing across all ocean-based climate sectors to implement solutions in a synergistic and nature-positive manner. For example, the US Government has developed a national mCDR research strategy that aims to promote research into the efficacy, safety and trade-offs of different mCDR methods [32].

3. Prioritise nature-based solutions. Protect and restore coastal ecosystems, such as mangroves, seagrasses and tidal marshes, recognising their no-regrets approach in climate mitigation and alignment with the Kunming–Montreal Global Biodiversity Framework. For example, the Indonesian Government has included blue carbon restoration within its NDCs [33].

4. Initiate steps to replace offshore oil and gas in the global energy supply with renewable energy. Initiate conversations and establish governance to halt new oil and gas exploration and phase down current production through demand-led mechanisms. At the same time, align efforts with respect to the scaling of renewable energy, ensuring a just and equitable transition to maximise social and environmental benefits. For example, the UK Government has proposed banning new offshore oil and gas drilling licences in the North Sea and promoting a transition to renewable energy technologies and carbon capture and sequestration [34].

5. Make the necessary capital investments to decarbonise maritime transport. Take urgent measures to reduce emissions from shipping and cruise tourism, capitalising on the potential and urgency of these vital sectors and assisting in their rapid transition to zero carbon. For example, the UK Government Department for Transport has developed a maritime decarbonisation strategy that includes continued research and development support for maritime decarbonization through the UK SHORE programme [35].

6. Strengthen ocean-based climate finance. Prioritise a more coherent approach to ocean-climate finance, aligning finance towards nature positive and net zero pathways, so that USD 2 trillion is directed towards ocean-based climate solutions between 2030 and 2050 [1]. Explore innovative financing models, including blended finance, to support nature-based solutions and other ocean-based initiatives. For example, in 2018, the Government of the Republic of Seychelles launched the world’s first sovereign blue bond. This has served as a blueprint for their further issuance worldwide [36].

7. Monitor, evaluate and correct. Implement robust monitoring, evaluation and adaptive management mechanisms across all ocean-based mitigation options to measure progress and correct any unintended consequences, ensuring that solutions remain on track. For example, the National Ocean Program of the Government of Chile includes an iterative process of monitoring, evaluation and adaptation at its core to ensure that it remains an effective and current ocean management approach [37].

8. Encourage and provide incentives for international cooperation. Enhance international cooperation, improve governance, and establish effective policies to address ocean challenges collaboratively. The Ocean Panel was established in 2018 with this in mind, with its 2024 progress report stating that 9 of 18 members are now either implementing and/or updating Sustainable Ocean Plans to achieve 100% sustainable management of their national waters, with a further four members in the final development stages of their plans [38].

9. Align ocean-based and terrestrial solutions. Recognise that ocean-based climate solutions are not standalone measures and hence must be accompanied by deep cuts in emissions from terrestrial sources of GHGs; this includes rapidly phasing down fossil fuels, expanding sustainable food systems, and increasing carbon sequestration in forests and terrestrial ecosystems. For example, the mitigation potential of ocean-based food is closely linked to the development of more sustainable terrestrial food systems [39].

10. Embrace urgency, inclusivity, and fairness. Emphasise the need for immediate and coordinated action from governments, businesses, civil society, and individuals to protect and restore the ocean’s health while adopting sustainable ocean-based solutions. This was emphasised, for example, within the final declaration of UNOC 3—“We must act with urgency to face this challenge [of declining ocean health] with bold, ambitious, just and transformative action, and ensure all people…are fully and meaningfully empowered and included in ocean-related decision-making…” [40].

4. Finance: The Missing Link

Realising the full potential of ocean-based climate solutions is estimated to require over USD 3 trillion in investment to 2050 [1,41,42]. This includes:

• USD 1 trillion by 2030 to scale mature solutions, such as offshore wind;
• USD 1.4–1.9 trillion for decarbonising shipping;
• USD 55 billion for sustainable aquaculture;
• USD 15 billion for mangrove restoration.

However, current levels of ocean finance fall drastically short of this—Sustainable Development Goal (SDG) 14, ‘Life below water’, is the least funded of all 17 SDGs, receiving less than 1% of total SDG finance to date [43].

Bridging the finance gap will require innovative solutions, new partnerships, and the re-aligning of finance flows with nature-positive and net zero pathways [44]. Blended finance, carbon markets, and redirected fossil fuel subsidies are key to unlocking this capital [45]. Greenhouse gas pricing may additionally generate USD 40–80 billion annually for ocean climate action [1].

5. Wider Impacts and Trade-Offs

Enacting ocean-based climate mitigation options requires trade-offs, with both positive and negative wider impacts with implications for sustainable development, human well-being, and governance [1]. While many interventions offer significant co-benefits such as enhanced biodiversity, improved fisheries, coastal resilience, and economic opportunities, they also involve trade-offs that must be carefully managed. Positive impacts may include biodiversity gains and ecosystem service improvements [17], economic growth through job creation and enhanced investment [28,46], and health and food security benefits from dietary shifts [1,26,47]. However, risks include environmental and social impacts from poorly planned aquaculture and renewable energy expansion, potential harm from unregulated marine carbon dioxide removal (mCDR) technologies, and ethical concerns and governance gaps [1,29,48]. Given the importance of, for example, geographic, political, and economic contexts, the balance of benefits and costs should be examined on a case-by-case basis.

Inclusive governance, stakeholder engagement, and tools like Sustainable Ocean Plans are important to ensure equitable outcomes [28]. Without these, interventions may exacerbate inequalities, particularly for small-scale fishers and coastal communities [28]. Well-designed, participatory approaches are essential to maximise benefits and minimise harm.

6. Conclusions

The ocean is not a silver bullet for climate change—but it is a powerful ally. With the right investments, policies, and partnerships, ocean-based solutions can help close the climate emissions gap by providing approximately a third of the mitigation needed to keep the Paris Agreement’s 1.5 °C goal within reach, whilst also helping to build climate resilience and deliver a sustainable ocean economy. Solutions including phasing out offshore oil and gas and deploying offshore renewable energy infrastructure are ready to implement now and need to be actioned urgently. However, achieving the full potential of ocean climate solutions will require the translation of pledges into action; partnering to fill knowledge gaps; a just transition in sectors, including the replacement of offshore oil and gas by renewable energy technologies; strengthening of climate finance and significant capital investments; alignment and collaboration with terrestrial climate solutions; and monitoring, evaluation, and course correction as necessary.

As countries prepare new NDCs ahead of COP 30, there is a rare opportunity to mainstream the ocean into global climate strategies. The Blue NDC Challenge, launched by Brazil and France during the 3rd UN Ocean Conference, calls on all nations to place the ocean at the heart of their climate plans—recognising its vital role in both mitigation and adaptation. COP 30 marks the 30th anniversary of UN climate summits and 10 years since the Paris Agreement was signed. It is a pivotal moment to assess progress, recalibrate global efforts to meet the 1.5 °C target, and mainstream ocean solutions within climate discourse and investment.