Glossary of road map assessment parameters

Description of approach A brief description of the proposed approach to slow the loss of Arctic sea ice and relevant background information.

• Marine Cloud Brightening (MCB) is a strategy for adding particles to the lower atmosphere to increase the abundance or reflectivity of low-lying clouds over particular regions of the ocean (NASEM 2021). MCB enhances cloud brightness by increasing the number of particles that act as cloud condensation nuclei (Feingold et al. 2024). The most appropriate clouds for MCB are marine stratocumulus clouds which are low elevation, large, and thick clouds, found in the eastern side of subtropical ocean basins (Russell et al. 2012). This idea stems from observations of bright features formed from pollution of ships moving in the ocean (“ship tracks”; Diamond et al. 2020). The International Meteorological Organization’s 2020 rule (IMO 2020) decreased the amount of sulfur allowed in shipping fuels for commercial vessels. These polluting aerosols reflected sunlight, and decreases in these aerosols have led to a reduction in clouds and cloud properties (Watson-Perris et al. 2022, Yuan et al. 2022, Diamond 2023), including brightness, and subsequently increased warming over the global ocean (Yuan et al. 2024). Also see the section for Marine Cloud Brightening: Arctic for details about Arctic-specific application.

Description of what it does mechanistically A brief description of the physical process of the approach and its intended impact(s).

• Expected physical changes (global)
  • Reduce incoming solar radiation; MCB would not directly affect sunlight in areas where not applied.
• Expected physical changes (Arctic region)
  • Reduce incoming solar radiation; MCB would not directly affect sunlight in areas where not applied.

Spatial extent (size) The spatial size proposed for application of the approach. When possible, this is provided in terms of area (km²).

• <20 – 50% of Earth’s surface
  • Stratocumulus regions make up 20% of the Earth’s surface (Wood 2012). It is unlikely that the entire area of stratocumulus clouds would be seeded with marine cloud brightening. It’s possible that other types of clouds would be possible for MCB but marine stratocumulus are the most responsive to aerosols. Some modeling studies have simulated MCB over larger areas – for example, the modeling scenario in Wood (2021) was for 54% of the Earth’s surface. 20% of Earth’s surface is 101,920,000 km².

Where applied – vertically A description of where the approach would be applied in terms of the vertical dimension (e.g., stratosphere, troposphere, sea surface, etc.). For atmospheric approaches, the altitude of application is provided in km.

• Atmosphere / Troposphere (low); 0-3 km altitude

Where applied – geographically (regional vs global application, is it targeting the Arctic?) A description of where the approach would be applied spatially, indicating if application would be global or would be applied in a specific region or location, and if the approach would be applied within the Arctic region.

• Regions with marine stratocumulus clouds
  • These regions occupy 23% of the ocean surface (Wood 2012) and are most commonly found in the eastern side of subtropical ocean basins (Russell et al. 2012), in midlatitude oceans, and in undisturbed polar regions (Wood 2012).

When effective (summer, winter, all year) A description of when in time the approach would produce its desired result.

• MCB more efficiently cools days and summers than nights and winters, as it requires sunlight. It could be effective during other seasons at low latitudes. Note that while SRM won’t have a radiative forcing effect during night/winter, there will still be a climate impact at night/winter due to ocean heat capacity and atmospheric heat transport.

Impact on

Albedo A description of the approach’s potential impact on albedo - the fraction of light reflected by a surface. Albedo ranges from 0 (no reflectance) to 1 (total reflectance). The impact on albedo will refer to that of sea ice, ocean, land surfaces or for clouds in the atmosphere depending on the approach.

• Varies
  • 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 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 A description of the approach’s potential impact on global mean surface temperature (°C).
  • Decreases up to a few degrees C
    • Temperature decrease will depend on specifics of the deployment, including how large of an area and the amount of aerosols.
    • Model simulations of MCB targeting most susceptible clouds yield temperature decreases of 1-2.2°C compared to simulations without MCB, depending on the number of clouds seeded in models (Rasch et al. 2009).
    • A multi-model comparison with a global uniform deployment (50% increase in cloud droplet number concentrations globally in low clouds) over the period of 2020-2069 yielded median temperature decrease of 0.96°C, with a range of temperature decrease of 0.17-1.21°C, with MCB relative to continued climate change (Stjern et al. 2018).
• Arctic region A description of the approach’s potential impact on temperature within the Arctic region (°C).
  • Decrease of 0.8°C
    • Model simulation of deployment in three marine stratocumulus regions yielded a decrease of 0.8°C in the poles (Parkes et al. 2012).
    • However, temperature decrease will depend on specifics of the deployment, including how large of an area and the amount of aerosols.

Radiation budget

• Global A description of the approach’s potential impact on global radiative forcing (Wm^-2). For some approaches, this will be in regard to the surface radiative forcing. For atmospheric approaches, this will be in regard to the top of atmosphere (TOA) radiative forcing. For context, the global energy imbalance from human activities at the top of the atmosphere is 0.90 ±0.15 Wm^-2 (Trenberth and Cheng 2022).
  • Decreases of 0 to 5 W/m²
    • The amount of forcing will depend on specifics of the deployment, including how large of an area and the amount of aerosols.
    • Model simulations summarized in NASEM (2021) predict decreases of 1 to 2 W/m².
    • Multi-model study reported median decrease in radiative forcing of 1.9 W/m² with a range of 0.6-2.5 W/m² across models (Stjern et al. 2018).
    • Previous studies and results summarized in Kravitz et al. (2013) range from decreases of 0 to 5 W/m².
    • Study comparing radiative forcing of different intervention techniques reports decrease of 3.71 W/m² (Lenton and Vaughan 2009).
• Arctic region A description of the approach’s potential impact on radiative forcing in the Arctic (Wm^-2). For some approaches, this will be in regard to the surface radiative forcing. For atmospheric approaches, this will be in regard to the top of atmosphere radiative forcing. For context, the global energy imbalance from human activities at the top of the atmosphere is 0.90 ±0.15 Wm^-2 (Trenberth and Cheng 2022).
  • Unknown

Sea ice

• Direct or indirect impact on sea ice? This describes if the approach has a direct effect on sea ice or if the approach impacts sea ice indirectly through an impact on another aspect of the climate system, such as temperature.
  • Indirect via temperature reduction
• New or old ice? Approaches may impact sea ice via the formation of new ice, the reinforcement of older existing ice, or both.
  • Both
• Impact on sea ice A description of the approach’s potential impact on sea ice in terms of sea ice extent (m² or km²), area (m² or km²), thickness, or volume (m³), dependent on what is reported in the scientific literature.
  • The impact on sea ice will depend on specifics of the deployment, including how large of an area and the amount of aerosols.
  • Reduction of 3% of 2020 ice extent with MCB compared to a 76% reduction in 2020 ice extent without MCB (Latham et al. 2012).
  • MCB restores sea ice minimum extent within 2% of 2009 levels with a high level of global seeding (Rasch et al. 2009).
  • In modeling simulation, sea ice extent with MCB extends further than control or with climate change (Latham et al. 2014).

Scalability

Spatial scalability Ability to replicate and expand the approach to the appropriate spatial scale to have an impact.

• Unknown. Currently not scalable.
  • Scalability will be a function of how different cloud regimes respond to forcing.

Efficiency Here we define efficiency as the ratio of impact on radiative forcing to the amount of energy required for the approach ((Wm^-2) J^-1).

• Unknown
  • 1500 wind-powered, unmanned spray vessels, each using 150kW, would be needed to produce the globally averaged negative forcing of -3.7 W/m² to balance carbon dioxide doubling (Latham et al. 2012). A conventional ship might consume about 1MW.

Timeline to scalability The estimated time until this approach could be scalable for deployment.

• Unknown

Timeline to global impact (has to be within 20 yr) The estimated time until this approach could have a global impact on climate change in terms of temperature or radiative forcing. Consistently ice-free conditions in September are expected by mid-century, with daily ice-free conditions expected ~4 years earlier (Jahn et al. 2024). Therefore, having a timeline to impact within 20 years might prevent ice-free conditions.

• > 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) The estimated time until this approach could have an impact on sea ice in the Arctic. Consistently ice-free conditions in September are expected by mid-century, with daily ice-free conditions expected ~4 years earlier (Jahn et al. 2024). Therefore, having a timeline to impact within 20 years might prevent ice-free conditions.

• > 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 The estimated cost of applying this approach ($USD) per relevant metric for the approach when available (e.g., $USD per 1ºC temperature decrease).

• Unknown
  • Costs may be similar to global SAI (NASEM 2021).

CO₂ footprint The estimated energy required to apply this approach (CO₂(t)) per relevant metric for the approach when available (e.g., CO₂(t) per 1ºC temperature decrease).

• 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).

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 some co-benefits and risks described for MCB depend on the modeling scenario used.

Physical and chemical changes

• Co-benefits Potential beneficial impacts to the physical or chemical domain due to application of the approach.
  • Enhanced oceanic upwelling could occur (Russell et al. 2012).
  • Potential for increased salt aerosols to reduce tropospheric ozone pollution (Horowitz et al. 2020).
• Risks Potential negative impacts to the physical or chemical domain due to application of the approach.
  • Changes to regional precipitation regimes (Russell et al. 2012, Bala et al. 2010, Stjern et al. 2018) due to spatially heterogeneous forcing patterns. MCB could enhance tropical land precipitation while decreasing ocean precipitation (relative to non-SRM baseline) due to preferential cooling over oceans.
    • Sahel droughts potentially in part caused by North American and European air pollution over the North Atlantic provide evidence that these spatial patterns could be important (Hirasawa et al. 2022).
  • Light reduction over the ocean under the clouds up to 50 W/m² at surface in stratocumulus regions (Russell et al. 2012).
  • Changes in the ratio of direct to diffuse light (Russell et al. 2012).
  • As a result of global temperature reduction, there may be significant regional cooling, which some modeling studies predict will perturb atmospheric-oceanic systems such as the West African Monsoon and the El Niño Southern Oscillation (Russell et al. 2012).
  • Potential effects on local salinity of surface seawater (Russell et al. 2012).
  • Potential changes in ocean circulation (Russell et al. 2012); Changes due to changes in energy flux with reduced atmospheric temperature (McCormack et al. 2016) in addition to changes from the clouds themselves.
  • Potential changes in surface temperature gradients (Russell et al. 2012).
  • Potential changes to oceanic upwelling patterns (Russell et al. 2012).
  • Potential changes to El Niño patterns (Russell et al. 2012).
  • Potential transport and deposition of sea spray to land (Russell et al. 2012).
  • Intense regional cooling could change ocean productivity and circulation, with subsequent effects on land, stratification, nutrient supply, and sunlight (Russell et al. 2012).
  • Large changes in atmospheric circulation and precipitation could impact terrestrial biogeochemical cycling and ocean chemical cycling (Russell et al. 2012).
  • Enhanced upwelling could increase outgassing of CO₂ (Russell et al. 2012).
  • Changes in circulation could impact climate regulation abilities of ocean (Russell et al. 2012).

Impacts on species

• Co-benefits Potential beneficial impacts to species due to application of the approach.
  • Potential benefits for coral cover due to reduced bleaching (Condie et al. 2021, Butcherine et al. 2023).
• Risks Potential negative impacts to species due to application of the approach.
  • Reduction in sunlight could affect phytoplankton species distributions – favoring those that are better adapted to low light conditions (Russell et al. 2012).

Impacts on ecosystems

• Co-benefits Potential beneficial impacts to ecosystems due to application of the approach.
  • Enhanced upwelling could increase nutrient supply and net primary productivity (Russell et al. 2012).
• Risks Potential negative impacts to ecosystems due to application of the approach.
  • PAR reduction could alter the depth of the chlorophyll maximum with unknown consequences to marine ecosystems (Russell et al. 2012).
  • Changes in phytoplankton species composition due to decreased light availability could have impacts higher up in food webs.
  • Changes in the ratio of direct to diffuse light could impact ecosystems (Russell et al. 2012, Diamond et al. 2022).
  • Potential for reduced net primary production (Partanen et al. 2016, Lauvset et al. 2017).

Impacts on society

• Co-benefits Potential beneficial impacts to society (human communities) due to application of the approach.
  • If upwelling enhanced, could have fisheries benefits for fisheries in upwelling areas (Russell et al. 2012).
• Risks Potential negative impacts to society (human communities) due to application of the approach.
  • Increased infrastructure in ocean areas (Russell et al. 2012).
  • Potential for reduced visibility at sea (Russell et al. 2012), although this will depend on the size of the aerosol used.

Ease of reversibility The ability of the environment and/or climate to revert to a state without application of the approach once an approach is stopped. While this section focuses on reversibility of the environment and/or climate impact, there is also mention of constraints on reversibility due to infrastructure related to the approach.

• 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 An estimate of the outcome(s) for the environment and/or climate if an approach were to be abruptly stopped.

• 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 A description of whether the approach would be subject to international or national jurisdiction for decisions or regulations related to research activities.

• 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 A description of existing treaties, laws, and regulations as well as codes of conduct and recommendations that might guide research into the approach. When available, descriptions will delineate existing governance for research versus deployment.

• 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: Global:
  • Marine scientific research is governed by the United Nations Convention on the Law of the Sea (UNCLOS).
    • 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).
  • A 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.
  • SilverLining (2023) provides a roadmap for research with a focus on MCB.

Justice Here we define justice related to approaches to slow the loss of Arctic ice through distributive justice, procedural justice, and restorative justice. Following COMEST 2023, we consider questions of ethics through a justice lens.

• 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 Distributive justice is the protection of basic rights and the fair distribution of benefits and burdens across a society. This section answers the question, “are the benefits and costs of research or potential deployment of the approach distributed fairly while protecting the basic rights of the most vulnerable?” (DSG)
  • Applicable to all approaches within Solar Radiation Modification:
    • Impacts from solar geoengineering have the 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: Global:
    • 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 Procedural justice is the equal opportunity to influence the deliberations of governance structures to whom one is subject. It is also genuine accountability for those who exercise power in order to prevent domination or exploitation. This section answers the question, “Do all those affected have an opportunity to participate and have a say in how the approach will be researched, deployed, and governed?” (DSG)
  • 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: Global:
    • No additional information.
• Restorative justice Restorative justice is atonement for contemporary wrongdoing and reparations for historical injustice. This section answers the question, “Are there plans for those who could be harmed by the approach to be compensated, rehabilitated, or restored?” (DSG)
  • 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: Global:
    • No additional information.

Public engagement and perception Public engagement describes ways in which “researchers, funding institutions, and decision-making bodies aim to inform, understand, draw input from, and empower publics and stakeholders” (definition from DSG). This section describes how people have been engaged in research for a given approach, as well as capacity building efforts to build knowledge around science and governance. This section also provides information on public perception when available.

• 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: Global:
  • Some engagement with efforts growing
    • There is increasing media attention on MBC (e.g., Flavelle 2024).
    • Some recent media attention (e.g., CNBC, CBC, CNN, The Washington Post)  addresses emerging effects of the International Meteorological Organization’s 2020 rule (IMO 2020) that decreased the amount of sulfur allowed in shipping fuels for commercial vessels. These polluting aerosols reflected sunlight and decreases in these aerosols has led to a reduction in cloud brightness and increased warming (Diamond 2023).
    • The Marine Cloud Brightening Program recently launched the Coastal Atmospheric Aerosol Research and Engagement (CAARE) facility. The facility was put on hold due to permitting issues and questions around public engagement. Debates around public engagement for small scale MCB experiments are starting to arise as research progresses.
    • Substate actors could play an important role in public engagement and integration of outputs from engagement into research and governance (Jinnah et al. 2018).
    • There is engagement by the Reef Restoration and Adaptation Program with the public through community panels.
  • Public perceptions of MCB are uncertain, and the reduction of concerns about governance may depend on the perceived controllability of MCB (C2G 2021 Evidence Brief).

Engagement with Indigenous communities This section describes how Indigenous peoples and communities have been engaged in research for a given approach, as well as capacity building efforts to build knowledge around science and governance.

• 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: Global:
  • Some
    • A 2020 University of Sydney and Queensland University-led cloud brightening experiment by the Great Barrier Reef was carried out with the consent of the local Indigenous Manduburra organization, representing the traditional land and water owner, with an observer taking part in the experiment (Low et al. 2022).