Glossary of road map assessment parameters

Description of approach

• Marine Cloud Brightening (MCB) is a strategy for adding particles to the lower atmosphere (near the surface) in order to increase the abundance or reflectivity of low-lying clouds over particular regions of the ocean (NASEM 2021). An application of MCB for Arctic clouds has been proposed, although there is less known about this regional application versus global application or application focused on lower latitudes. MCB stems from observations of bright features formed from pollution of ships moving in the ocean (“ship tracks”; Diamond et al. 2020). Also see the section for Marine Cloud Brightening: Global.

Description of what it does mechanistically

• Expected physical changes (global)
  • Reduce incoming solar radiation in Arctic region; MCB would not directly affect sunlight in areas where not applied. Ability of this technique to have a global impact would depend on the scale of the approach.
• Expected physical changes (Arctic region)
  • Reduce incoming solar radiation in Arctic region; MCB would not directly affect sunlight in areas where not applied.

Spatial extent (size)

• Clouds over Arctic Ocean
  • Area of Arctic Ocean is 14,060,000 km².

Where applied – vertically

• Atmosphere / Troposphere (low); 0-1.5 km altitude (Kravitz et al. 2014)

Where applied – geographically (regional vs global application, is it targeting the Arctic?)

• Targeted deployment in Arctic into clouds over Arctic Ocean.

When effective (summer, winter, all year)

• Summer, and potentially also spring and fall to a lesser extent. MCB more efficiently cools days and summers than nights and winters.

Impact on

Albedo

• Increases in cloud albedo up to 0.23 reported in Arctic-specific study (Kravitz et al. 2014).
  • Changes in albedo will depend on many factors including how much aerosol is added, the background cloud state, and adjustments (Diamond et al. 2022).
  • MCB would provide surface shading, and not directly change surface albedo.
  • Climate model studies (in general, not Arctic-specific) show that MCB sea salt aerosol emissions cause large non-cloud atmospheric albedo changes (“direct aerosol forcing”; Ahlm et al. 2017, Mahfouz et al. 2023).

Temperature

• Global
  • Unknown
    • Temperature decrease will depend on specifics of the deployment, including how large of an area and the amount of aerosols.
• Arctic region
  • Unknown
    • Temperature decrease will depend on specifics of the deployment, including how large of an area and the amount of aerosols.

Radiation budget

• Global
  • Decrease of 0.45 W/m² reported in Arctic-specific study.
    • Decrease in radiative forcing of 0.45 W/m² averaged globally from MCB reported in Kravitz et al. (2014).
    • Amount of forcing will depend on specifics of the deployment, including how large of an area and the amount of aerosols.
• Arctic region
  • Decrease up to 10.94 W/m² reported in Arctic-specific study.
    • Modeling study report decrease in radiative forcing of 10.94 W/m² (Kravitz et al. 2014). Other modeling study reports that an order of magnitude more forcing required to preserve Arctic sea ice (Tilmes et al. 2014).
    • Amount of forcing will depend on specifics of the deployment, including how large of an area and the amount of aerosols.

Sea ice

• Direct or indirect impact on sea ice?
  • Indirect via temperature reduction, could also provide direct shading for Arctic sea ice. Direct surface/downwelling longwave radiation effects could reduce effectiveness.
• New or old ice?
  • Both
• Impact on sea ice
  • Unknown
    • Impact on sea ice will depend on specifics of the deployment, including how large of an area and the amount of aerosols.

Scalability

Spatial scalability

• Unknown

Efficiency

• Unknown

Timeline to scalability

• Unknown

Timeline to global impact (has to be within 20 yr)

• > 15 years
  • Unanswered questions about cloud-aerosol interactions.
  • Nozzle and delivery system under development (work in Australia by the Reef Restoration and Adaptation Program and in the United States by the University of Washington’s Marine Cloud Brightening Program).
  • It is possible that timeline could be escalated via governmental support.
  • Once implemented, SRM methods would have an impact within months (Russell et al. 2012 and references therein).

Timeline to Arctic region impact (has to be within 20 yr)

• > 15 years
  • Unanswered questions about cloud-aerosol interactions.
  • Nozzle and delivery system under development (work in Australia by the Reef Restoration and Adaptation Program and in the United States by the University of Washington’s Marine Cloud Brightening Program).
  • It is possible that timeline could be escalated via governmental support.
  • Once implemented, SRM methods would have an impact within months (Russell et al. 2012 and references therein).

Cost

Economic cost

• Unknown
  • No existing assessment in literature for Arctic-specific deployment (Duffey et al. 2023).

CO₂ footprint

• Unknown
  • Depends on fuel needed for ships and energy required for delivery of aerosols.
  • The energy demand is directly related to the mass of water pumped, which is dependent on the size of the aerosol produced (Connolly et al. 2014).

TRL

• 4 – MCB in general has received attention via modeling studies, observations of ship tracks from aerosol particles from ship exhausts, laboratory studies for delivering aerosols, and small-scale outdoor experiments in Great Barrier Reef. For an Arctic specific deployment, few modeling studies exist.
• Summary of existing literature and studies:
  • MCB generally:
    • Modeling studies (e.g., Stjern et al. 2018, Wood 2021), including those that include predictions for the Arctic (Parkes et al. 2012, Latham et al. 2012, 2014).
    • Observational studies of ship tracks from aerosol particles (Diamond et al. 2020) as well as studies of aerosol-cloud interactions (Russell et al. 2013).
    • Laboratory and modeling studies for delivering aerosols (Latham et al. 2012, Connolly et al. 2014, Salter et al. 2014).
    • Small-scale outdoor experiments in Great Barrier Reef (Tollefson et al. 2021, Hernandez-Jaramillo et al. 2023).
    • Frameworks proposed for future research (Diamond et al. 2022).
  • Arctic-specific MCB:
    • Modeling study by Kravitz et al. 2014. Most other studies looking at Arctic effects simulated a global or lower latitude deployment, then looked at Arctic effects.

Technical feasibility within 10 yrs

• Feasible
  • Depends on development of delivery nozzle and fleet of sprayers.
  • However, there is no existing assessment in literature for Arctic-specific deployment (Duffey et al. 2023).

Missing information in this section does not indicate the absence of risks or co-benefits; it simply reflects that sufficient information is not yet available. Note also that co-benefits and risks described for MCB depend on the modeling scenario used.

Physical and chemical changes

• Co-benefits
  • Cooling in the Arctic may decrease permafrost thaw.
• Risks
  • Large radiative forcing required to slow the loss of Arctic sea ice would likely cause large land-sea temperature gradients that would impact hydrological cycles (Kravitz et al. 2018 in Duffey et al. 2023).
  • It’s possible that changes in atmospheric heat distribution from MCB could counteract the benefits of MCB deployment (C2G 2021 Evidence Brief).
  • Prediction of remote effects from regional deployments change a lot between simulations of the current climate versus a future climate (Wan et al. 2024). While not modeling the Arctic specifically, a model of regional deployment in the North Pacific showed that MCB was less efficient in a future climate with further warming (Wan et al. 2024).

Impacts on species

• Co-benefits
  • Unknown
• Risks
  • Unknown

Impacts on ecosystems

• Co-benefits
  • Unknown
• Risks
  • Unknown

Impacts on society

• Co-benefits
  • Unknown
• Risks
  • Unknown

Ease of reversibility

• Easy
  • Aerosols in the troposphere remain for a few to ten days due to MCB (Latham et al. 2012, UNEP 2023), making this technique easy to reverse.

Risk of termination shock

• High
  • Could have rapid temperature increase if terminated (C2G 2021 Evidence Brief).

For an extensive list of resources on solar radiation management and governance see https://sgdeliberation.org/externalresources/.

International vs national jurisdiction

• Applicable to all approaches within Solar Radiation Modification:
  • International regulations would likely need to be considered for all Solar Radiation Modification approaches as transboundary effects are likely, especially for larger field experiments and deployment, dependent on scale and area of application. Some research activities may fall under national jurisdiction.
• Specific to Cirrus Cloud Thinning, Mixed-Phase Cloud Thinning, and Marine Cloud Brightening (Global and Arctic):
  • For activities occurring over/in the ocean:
    • If occurring within Exclusive Economic Zone would be governed by State (C2G 2021 Evidence Brief).
    • In International waters customary international law applies (C2G 2021 Evidence Brief).

Existing governance

• Applicable to all approaches within Solar Radiation Modification:
  • There is no formal governance framework for this approach (UNEP 2023). Governance efforts to date have been scattered and ad hoc (NASEM 2021). Governance is needed for at least two different levels: research and deployment (DSG). It will be important to distinguish small-scale perturbation experiments without climate relevance versus larger-scale testing that may be indistinguishable from deployment. In the absence of a governance framework there have been calls for governments to prohibit the development and deployment of SRM (Gupta et al. 2024). There is a need for governments to discuss coordination of research governance (Jinnah et al. 2024b).
  • Many organizations have released guidance and frameworks for governance, described below in order of publication year.
    • The National Academy of Sciences’ (2021) report “Reflecting Sunlight: Recommendations for solar geoengineering research and research governance landscape” provides an overview of laws and international treaties that might apply to SRM. These include:
      • Domestic Law
        • US National Environmental Policy Act and state analogs
        • US Weather Modification Reporting Act and state analogs
        • Regulatory statutes
        • Tort Liability
        • Intellectual property law
      • International Environmental Law
        • Treaty Law
          • UN Convention on Biological Diversity
          • London Convention/London Protocol
          • UN Framework Convention on Climate Change
          • Vienna Convention and Montreal Protocol
          • Convention on Long-Range Transboundary Air Pollution (CLRTAP)
          • Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques (ENMOD)
          • UN Convention on the Law of the Sea
        • Customary International Law and Principles
          • Prevention of transboundary harm principle
          • Principle of intergenerational equity
          • The precautionary principle
          • Sustainable development goals
    • NASEM (2021) also provides a proposed framework and approach for SRM research and governance, which emphasis engagement, input, and assessment. This includes exit ramps – “criteria and protocols for terminating research programs or areas” (NASEM 2021).
    • A report by the Climate Overshoot Commission (2023) calls for research on SRM and governance discussions as well as moratorium on SRM deployment and large-scale outdoor experiments.
    • UNESCO World Commission on the Ethics of Scientific Knowledge and Technology’s (COMEST) 2023 Report on the ethics of climate engineering has a slate of recommendations related to SRM covering governance, participation and inclusion, role of scientific knowledge and research strengthening capacity, and education, awareness, and advocacy.
    • An independent advisory committee for Harvard University’s Stratospheric Controlled Perturbation Experiment (SCoPEX) applied a research governance framework to the SCoPEx proposal detailed in the advisory committee’s final report (Jinnah et al. 2024a), which may inform future governance of outdoor experiments; this framework could potentially be applied to other atmospheric SRM approaches.
    • Funded by the European Union, Conditions for Responsible Research on SRM, Analysis, Co-Creation, and Ethos (Co-CREATE) outlines in their scoping note existing legal frameworks that could be relevant for SRM research and lays out a plan for developing a potential governance framework for SRM research (Co-CREATE 2024).
    • The American Geophysical Union released an Ethical Framework for Climate Intervention (AGU 2024) to guide responsible research, emphasizing the need for inclusive dialogue and expanded engagement. 
    • In 2024, the Group of Chief Scientific Advisors to the European Commission released an Evidence Review Report and an accompanying Scientific Opinion on Solar Radiation Modification. The Evidence Review Report outlines potential policy options on SRM research and deployment. The Scientific Opinion details five main policy recommendations. In summary, these recommendations were: 1) prioritize greenhouse gas emissions reductions, 2) agree to an EU-wide moratorium on SRM deployment, 3) negotiate a global governance system for SRM deployment, 4) ensure that SRM research is conducted responsibly, and 5) reassess the risks and benefits of SRM based on scientific evidence every 5-10 years (European Commission 2024).
  • Relevant to any research activities as well as deployment, the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) states that Indigenous Peoples have the right to determine how their lands and resources are used, and that to conduct any project affecting Indigenous Peoples’ lands or resources, free, prior and informed consent (FPIC) must be obtained through the Indigenous Peoples’ own representative institutions (UN 2007).
    • In Canada, the establishment of the National Council for Reconciliation provides a formal mechanism for Indigenous Peoples to hold all levels of government in Canada accountable for implementing UNDRIP, among other reconciliation actions (Bill C-29 2024). Canada maintains a nation-to-nation relationship with Indigenous Peoples (Government of Canada 2024).
• Specific to Marine Cloud Brightening: Arctic:
  • The Arctic Ocean is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which includes all Arctic coastal states except the United States. The United States, however, is bound to customary law “including customs codified or that have emerged from UNCLOS” (Argüello and Johansson 2022).
    • UNCLOS and marine scientific research (MSR):
      • MSR is governed by Part XIII of UNCLOS. In general, the right of states to conduct MSR is subject to the rights and duties of other states under UNCLOS (UNCLOS Article 238). There is a duty on parties to promote and facilitate MSR (UNCLOS Article 239).
      • MSR shall be conducted exclusively for peaceful purposes, it may not unjustifiably interfere with other legitimate uses of the sea, and it must be conducted in compliance with all relevant regulations adopted in conformity with the Convention, including those for the protection and preservation of the marine environment (UNCLOS Article 240).
      • States are responsible and liable for damage caused by pollution of the marine environment arising out of MSR undertaken by them or on their behalf (UNCLOS Article 263(3)).
        • Any approaches that involve adding material or energy to the ocean that would cause or be likely to cause damage to the marine environment would constitute “pollution of the marine environment” within the meaning of Article 1(1)(4) of UNCLOS, and States would have a duty to minimize the pollution pursuant to Article 194.
    • National Jurisdiction and MSR under UNCLOS
      • In a coastal state’s territorial sea (12 nautical miles from shore baseline), the coastal state has the exclusive right to regulate, authorize, and conduct MSR.
      • In a coastal state’s EEZ (200 nautical miles from shore baseline), coastal states also have the right to regulate, authorize, and conduct MSR, and MSR by other states requires the consent of the coastal state (UNCLOS Article 246(2)). States ordinarily give their consent, and they are required to adopt rules to ensure that consent is not delayed or denied unreasonably. UNCLOS further specifies grounds for refusing consent, including if the MSR involves introducing harmful substances into the marine environment (UNCLOS Article 246(5)(b)).
    • Areas outside National Jurisdiction and MSR under UNCLOS
      • On the high seas, UNCLOS provides for freedom of MSR (UNCLOS Article 87(1)(f)), but it must be done with due regard for the interests of other States in their exercise of the freedom of the high seas (Articles 87(2)).
      • The high seas are reserved for peaceful purposes (Article 88) and no state may subject a portion of high seas to its sovereignty (Article 89).
  • For an Arctic-specific application, the 2017 Agreement on Enhancing Arctic Scientific Cooperation is relevant. This is a legally binding agreement signed in 2017 by all Arctic States negotiated in the Arctic Council. It promotes international cooperation and favorable conditions for conducting scientific research, facilitates access to research areas, infrastructure, and facilities, and promotes education and training of scientists in Arctic issues. The agreement also encourages participants to utilize traditional and local knowledge as appropriate as well as encourages communication between traditional and local knowledge holders and participants. This may provide a framework for consultation with stakeholders including Indigenous peoples in intervention research, planning, and testing (Chuffart et al. 2023).
  • The Arctic Council has been called upon as a venue for providing oversight on regional approaches to slow the loss of Arctic sea ice, or to establish working groups to provide guidance (Bodansky and Hunt 2020, Bennett et al. 2022). However, the current geopolitical landscape and lack of participation from Russia makes consensus difficult.
  • Research framework was proposed by Diamond et al. (2022) which includes checkpoints (research questions that need to be addressed for the pathway to be viable) and exit ramps (criteria for terminating research if the pathway is deemed not technically or socially feasible). This type of research framework could be enacted now, even in the absence of other governance structures and international guidance. Diamond et al. (2022) focuses on physical and technical checkpoints and exit ramps. However, social checkpoints and exit ramps also need development.
  • OSTP (2023) provides a research governance framework and research plan for United States SRM activities, focusing on SAI, CCT, and MCB; it is not Arctic-focused. Also see Wanser et al. (2022) for a roadmap approach for the planning, coordination, and delivery of research to support scientific assessment of SRM.

Justice

• See DSG (2023), A justice-based analysis of solar geoengineering and capacity building.
• Here we define justice related to approaches to slow the loss of Arctic sea ice through distributive justice, procedural justice, and restorative justice. Following COMEST (2023), we consider questions of ethics through a justice lens. Note that this is not an exhaustive list of justice dimensions and as the field advances, so will the related considerations and dimensions.
• General comment on justice: “A well-designed mission-driven research program that aims to evaluate solar geoengineering could promote justice and legitimacy, among other valuable ends. Specifically, an international, mission-driven research program that aims to produce knowledge to enable well-informed decision-making about solar geoengineering could (1) provide a more effective way to identify and answer the questions that policymakers would need to answer; and (2) provide a venue for more efficient, effective, just, and legitimate governance of solar geoengineering research; while (3) reducing the tendency for solar geoengineering research to exacerbate international domination” (Morrow 2019).
• Distributive justice
  • Applicable to all approaches within Solar Radiation Modification:
    • Impacts from solar geoengineering have potential to cause disproportionate harm to those least responsible for climate change (DSG 2023). It is also possible that communities most exposed or vulnerable to climate hazards receive the most benefit, depending on the deployment. There is concern from vulnerable populations that research will overlook local needs and worsen global inequities (C2G 2021 Evidence Brief). There is an urgent need for justice-based recommendations (DSG 2023).
  • Specific to Marine Cloud Brightening: Arctic:
    • MCB has the potential to drive regional differences in the earth system with subsequent impacts on species, ecosystems, and society. The costs and benefits of this approach may be inequitably distributed.
• Procedural justice
  • Applicable to all approaches within Solar Radiation Modification:
    • If procedural justice is considered, people affected by research would have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed. Because these approaches have global ramifications, procedural justice will be challenging (Preston 2013).
    • Efforts to support procedural justice for SRM in general to date have been inadequate (DSG 2023). Because of uncertainty in outcomes, variable interests, and the potential for wide-ranging effects, procedural justice is critical (DSG 2023).
    • Diversity within the SRM research community has generally been lacking (NASEM 2021). To address this, some organizations have supported participation in research for the Global South, but there has been a lack of attention on support for participation in governance (DSG 2023). Therefore, organizations and people may understand the science of an approach but not know how to translate their interests around the issue into policy, which is a significant justice gap (DSG 2023).
    • Bennett et al. (2022) suggests an inclusive governance approach that incorporates stakeholder concerns in the design and deployment of approaches and effectively communicates risk. Within the development of such a framework there is an opportunity to prioritize procedural justice (Morrow 2019) and Indigenous self-determination (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
  • Specific to Marine Cloud Brightening: Arctic:
    • No additional information
• Restorative justice
  • Applicable to all approaches within Solar Radiation Modification:
    • If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored (Preston 2013).
    • Horton and Keith (2019) proposed an international climate risk insurance pool where states supporting SRM deployment support the pool and opposing states would be insured against SRM risks.
  • Specific to Marine Cloud Brightening: Arctic:
    • No additional information

Public engagement and perception

• Applicable to all approaches within Solar Radiation Modification:
  • There have been a series of open letters from academics and others that reject (Call for Non-Use Agreement) or support (Importance of Research on SRM, Call for Balance) solar radiation modification research, showing the current varying opinions that are shaping public perception.
  • The SCoPEx independent advisory committee offered four core principles for societal engagement related to solar radiation modification:
    • Start engagement efforts as early as possible.
    • Include social scientists with engagement expertise on research teams during the research design process.
    • Don’t presuppose what communities will be concerned about.
    • Develop a plan to be responsive to community concern.
  • A recent study on public perceptions found that people surveyed in the Global South were generally more supportive of research and development into SRM technologies compared to those from the Global North (Baum et al. 2024). Those from the Global South also expressed concern about unequal distribution of risks between rich and poor countries (Baum et al. 2024).
• Specific to Marine Cloud Brightening: Arctic:
  • Unknown if there is engagement for Arctic specific research and deployment
    • Substate actors could play an important role in public engagement and integration of outputs from engagement into research and governance (Jinnah et al. 2018).

Engagement with Indigenous communities

• Applicable to all approaches within Solar Radiation Modification:
  • The principle of free, prior, and informed consent (FPIC) in the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) is the foundation for engagement with Indigenous Peoples.
  • Particular to any potential Arctic research or deployment, The Inuit Circumpolar Council (2022) has published Circumpolar Inuit Protocols for Equitable and Ethical Engagement, which include eight protocols:
    • ‘Nothing About Us Without Us’ – Always Engage with Inuit
    • Recognize Indigenous Knowledge in its Own Right
    • Practice Good Governance
    • Communication with Intent
    • Exercising Accountability – Building Trust
    • Building Meaningful Partnerships
    • Information, Data Sharing, Ownership, and Permissions
    • Equitably Fund Inuit Representation and Knowledge
  • Any meaningful engagement with Indigenous peoples needs to consider context. Whyte (2018) states, “Indigenous voices should be involved in scientific and policy discussions of different types of geoengineering. But, context matters. Geoengineering discourses cannot just be associated with geoengineering to the exclusion of topics and solutions that Indigenous peoples value.”
  • European Union-funded Co-CREATE is pursuing a co-creation approach with Indigenous communities in their work to develop a potential governance framework for SRM research (Co-CREATE 2025).
• Specific to Marine Cloud Brightening: Arctic:
  • Unknown for Arctic specific research and deployment