Marine geoengineering

Marine geoengineering refers to attempts to manipulate the ocean to counteract the effects of climate change by removing carbon dioxide from the atmosphere through deliberate ocean‐based interventions, ranging from stimulating plankton blooms and enhancing alkalinity, to brightening clouds to make them more reflective, designed to remove CO₂.

The London Convention (1972) and the more modern, London Protocol (1996), are the two main international treaties of global application addressing the protection the marine environment from pollution caused by the dumping of wastes and other matter into the sea, and at international level provide the only explicit governance of marine geoengineering.

What is marine geoengineering?

Marine geoengineering is defined under the London Protocol as "a deliberate intervention in the marine environment to manipulate natural processes, including to counteract anthropogenic climate change and/or its impacts, and that has the potential to result in deleterious effects, especially where those effects may be widespread, long-lasting or severe".

Numerous other terms have been used to collectively refer to marine geoengineering techniques, including 'climate engineering', 'climate related geoengineering', 'climate intervention', and 'climate remediation'. Proposed marine geoengineering techniques are often divided into two groups: those intended to remove CO₂ from the atmosphere (marine carbon dioxide removal (mCDR)) and those intended to reduce the amount of solar energy that is absorbed by the Earth's surface (solar radiation management (SMR)).

Marine carbon dioxide removal (CDR)

Techniques proposed to draw down and lock away CO₂ by either enhancing the ocean's biological carbon pump, increasing the chemical carbon sink, include:

Ocean fertilization: Adding iron, or other micronutrients such as nitrogen or phosphorus, to the ocean to stimulate phytoplankton blooms that draw down CO₂ from the atmosphere, which in turn results in enhanced carbon sequestration via the biological pump and, potentially, carbon dioxide removal.
Biomass (macroalgae and crop-waste) sinking: Growing macroalgae, or gathering macroalgae floating in the ocean (e.g. Sargassum species) or crop waste and sinking in the deep ocean to remove CO₂.
Artificial upwelling: The process of bringing nutrient-rich waters from deep in the ocean to the surface, to stimulate biological activity, such as phytoplankton growth and to sequester atmospheric CO₂.
Ocean alkalinity enhancement: Dissolving alkaline materials (e.g. ocean liming, or adding alkaline rock powders) or via electrochemical methods, to boost seawater's natural CO₂ uptake.

Solar Radiation Management (SRM)

Methods proposed to reflect sunlight to cool the planet can include:

Marine cloud brightening: Injecting fine sea salt or other particles into shallow clouds to brighten them, increasing their reflectivity and reducing the amount of heat absorbed by the water below.
Ocean albedo enhancement: Increasing the reflectivity, or albedo, of the surface of the ocean to reflect sunlight into space and reduce warming, this can include the following types: microbubbles, foams, ice, reflective algal blooms and other reflective materials.

Ocean Interventions for climate change mitigation - overview

WG 41:Ocean Interventions for Climate Change Mitigation | GESAMP

What are some of the marine geoengineering techniques being proposed?

Technique	How it works	Potential benefit	Key consideration
Ocean fertilization	Disperse nutrients (e.g. iron) to spur phytoplankton blooms; sinking biomass sequesters CO₂.	Enhances biological carbon pump	May disrupt food webs, cause harmful algal blooms
Biomass (macroalgae and crop-waste) sinking	Sinking macroalgae or crop waste in the deep ocean to sequester the carbon they contain.		May affect nutrient cycling, reduce phytoplankton production and smother seabed
Artificial upwelling	Pumping cold, nutrient-rich deep water to the surface, boosting productivity and carbon export.	Draws down CO₂ supports fisheries	Risk of depleting deep-water nutrients and oxygen
Enhanced alkalinity	Adding alkaline material (e.g. olivine) to seawater, increasing its capacity to absorb CO₂.	Chemical CO₂ removal
Marine cloud brightening	Spray fine sea-salt or reflective aerosols into marine clouds to increase reflectivity.	Rapid regional cooling potential	Uncertain impacts on weather patterns
Ocean albedo enhancement	Deploy reflective foams or films on the water surface to reflect sunlight back to space.	Direct solar radiation reduction	Potential effects on marine life and water quality

In 2019, GESAMP – Working Group 41 published its High Level Review of a Wide Range of Proposed Marine Geoengineering Techniques report, providing a high-level review of 27 proposed marine geoengineering techniques. Most fall under carbon dioxide removal (CDR) strategies, while others address indirect effects like hurricane weakening or harnessing ocean thermal energy conversion (OTEC). The report assesses methane capture and destruction methods for their potential in meeting climate targets. The report called for the rapid development of international governance and risk-assessment frameworks, reflecting the London Protocol's precautionary approach.

The report emphasizes that robust international cooperation and comprehensive scientific research are essential: each technique must undergo a holistic risk–benefit assessment to understand its ecological and social impacts before any large-scale deployment.

GESAMP WG 41 is currently developing an Integrated Assessment Framework. This framework is essential to promote a transition towards a more holistic assessment that includes social, political, economic, ecological, ethical and other societal dimensions.

Where can I find a list of current marine geoengineering activities?

The current proposals on ocean climate interventions that GESAMP WG 41 is aware of (as of May 2024) can be found here.

Why is marine geoengineering important?

Since net-zero greenhouse gas emissions targets have become a keystone of climate policy, there has been increasing debate about the need to complement urgently needed emission reductions with active removal of carbon dioxide from the atmosphere. As the ocean already plays a key role in regulating the global climate by absorbing about a quarter of current CO₂ emissions, marine geoengineering techniques are gaining increasing attention as a potential way to further increase the ocean's capacity to remove carbon dioxide from the atmosphere to mitigate climate change.

How is marine geoengineering regulated?

At the international level, the London Convention (LC) and the London Protocol (LP) provide the only explicit governance of marine geoengineering. The LC and LP regulate marine geoengineering activities, such as ocean fertilization, which could have large-scale and potentially long-lasting effects on the maritime environment. This precautionary approach helps ensure that such interventions are carefully assessed and managed to protect ocean health and biodiversity.

2008: The LC/LP Parties adopted resolution LC-LP.1(2008) deciding that ocean fertilization activities other than legitimate scientific research should not be allowed.
2010: Parties adopted resolution LC-LP.2 (2010), an "Assessment Framework for Scientific Research Involving Ocean Fertilization" (OFAF), which proposed that research projects should be assessed to determine if they qualify as legitimate scientific research.
2013: The Parties adopted resolution LP.4(8)) (LC/LP, 2013) that amends the LP and prohibits all "marine geoengineering" activities, with the exception of those listed in Annex 4 and deemed "legitimate scientific research" according to an assessment framework put forward in Annex 5. When in force, this amendment will create a legally binding regime providing a science based, global, transparent and effective regulatory and control mechanism for marine geoengineering. The amendment enables the future regulation of marine geoengineering techniques that fall within the scope of LP and have the potential to cause widespread, long-lasting or severe impacts on the marine environment.

Currently, ocean fertilization is the only marine geoengineering activity listed under the new Annex 4. However, several other techniques are being considered by the LC/LP Parties.

Key elements of LP's marine geoengineering regime include:

Prohibition of ocean fertilization: Resolution LP.4(4) (2008) bans all large-scale fertilization, permitting only bona-fide scientific research subject to rigorous risk assessment.
Listing of authorized techniques: The 2013 amendment (Resolution LP.4(8)) created a "positive list" (Annex 4) of geoengineering methods. Only those proven safe may proceed.
Environmental risk assessments: Annex 5 mandates a standardized risk assessment and management framework; LC/LP Scientific Groups develop and review these guidelines.
Permitting system: Article 6bis requires each Party to issue a national permit, binding operators to monitoring, reporting and contingency measures under IMO oversight.

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Ensuring a precautionary approach to marine geoengineering

The London Protocol (LP) encompasses a precautionary approach, outlined in Article 3 of the LP, which has been applied to marine geoengineering activities. This precautionary approach means that the absence of full scientific certainty about potential harm is not a valid reason to delay measures to prevent environmental damage. Parties have signaled their determination to ensure that the protection of the marine environment is at the forefront when considering ocean-based climate change mitigation measures.

In 2025, the 47th Consultative Meeting of Contracting Parties to the London Convention and the 20th Meeting of Contracting Parties to the London Protocol (LC 47/LP 20) continued discussions on marine geoengineering, building on the discussions that started in previous LP/PC meetings, emphasizing that protecting the marine environment must remain central in ocean-based actions to address climate change.

The governing bodies issued a statement highlighting the growing number of MGE activities, including those conducted by private or commercial companies that by their nature and scale are of relevance to all countries and have the potential to result in deleterious effects. The governing bodies also expressed concerns on the possible environmental, social, and economic impacts on developing countries, especially Least Developed Countries (LDCs) and Small Island Developing States (SIDS). They confirmed their commitment to advancing scientific understanding of marine geoengineering techniques to inform their potential actions.

The governing bodies agreed to re-establish the intersessional Correspondence Group on marine geoengineering to continue working and report to the next LC/LP meeting in October 2026. The group will focus on clarifying how the London Convention and Protocol apply to marine geoengineering, refining definitions for the priority MGE techniques under review, clarifying the application of the revised Ocean Fertilization Assessment Framework and the draft assessment frameworks for other techniques, and advise on steps to support their implementation.

Clear regulations adapted to emerging technologies are indispensable and should be based on scientific evidence and research, for example, as provided through the GESAMP Working Group 41. Based on the established regulatory framework for marine geoengineering, the LC/LP is often perceived as a primary means of further regulating other mCDR and SRM methods. The LC/LP regime allows for an interdisciplinary approach where ethical and technological discussions, among others, can take place and which require expertise and exchanges from and among different stakeholders.

What are the environmental and ethical concerns surrounding marine geoengineering?

Proposed marine geoengineering techniques, which involve deliberate large-scale manipulation of the environment, raise significant environmental and ethical concerns. The GESAMP WG 41 high-level review (2019) highlights some of those concerns:

Environmental Concerns

1. Ecosystem Disruption

Unintended trophic effects: Adding nutrients (e.g. for ocean fertilization) can trigger harmful algal blooms, oxygen depletion, or shifts in species composition.
Chemical imbalances: Techniques like alkalinity enhancement may alter local pH, trace‐metal cycling, or carbonate chemistry in ways that cascade through marine food webs.
Weather & climate feedback: Solar-radiation management (e.g. marine cloud brightening) could change regional precipitation, storm patterns, or ocean circulation, with knock-on environmental impacts.

2. Biodiversity Risks

Habitat loss: Changes in light penetration or nutrient regimes can degrade critical habitats (coral reefs, seagrass beds).
Invasive species: Altered conditions may favour opportunistic or non-native species, reducing native diversity.

3. Permanence & Reversibility

Lock-in effects: Some interventions (e.g. sub-sea CO₂ injection) are effectively irreversible on human timescales. Any unforeseen leak or failure could be impossible to remedy.
Long-term monitoring: Ensuring stored CO₂ remains sequestered, or that cloud-brightening particles do not accumulate, requires multi-decade (or longer) oversight.

Ethical and Governance Concerns

1. Moral Hazard

Reduced mitigation incentive: Reliance on geoengineering could distract from deeper emissions cuts, giving a false sense of security or "quick fix" mentality.

2. Justice & equity

Transboundary impacts: Ocean currents and climate effects do not respect national borders. Some nations or communities (often in the Global South) could bear disproportionate risks without having a say.
Intergenerational equity: Decisions made today may commit future generations to stewardship of altered ocean states or long-term monitoring burdens.

3. Consent & participation

Stakeholder engagement: Local communities, Indigenous peoples, and developing nations must have a meaningful voice in decisions that affect shared oceans.
International governance: Current treaty frameworks (London Protocol, UNCLOS) are geared toward environmental protection, but gaps remain around consent processes and benefit-sharing for geoengineering activities.

4. Transparency & accountability

Research opacity: Small-scale experiments in remote waters risk "slippery slope" progression to large-scale deployment absent clear public disclosure.
Liability & remediation: If harmful effects occur, determining who is responsible and how to remediate environmental damage may be legally and practically complex.

In other words, while marine geoengineering holds promise as a complementary tool for climate mitigation, its environmental side effects and ethical implications demand rigorous, transparent governance; robust impact assessments; long-term monitoring; and inclusive decision-making to ensure interventions do not trade one crisis for another.

GESAMP WG 41 is developing an Integrated Assessment Framework (IAF) to holistically assess relevant scientific and societal issues that may arise about potential ocean interventions, primarily for climate change mitigation.