Glossary of road map assessment parameters

Description of approach

• Methane (CH₄) is a potent greenhouse gas responsible for about 30% of the rise in global temperature since the industrial revolution (IEA 2024). Per ton, methane has > 80 times the warming of carbon dioxide over a 20-year timeframe, despite persisting in the atmosphere for a shorter period of time, on the order of a decade (IPCC 2021, IGSD 2023, Spark Climate Solutions 2024). Methane is also a precursor of tropospheric ozone and plays an important role in complex, non-linear atmospheric chemistry. Atmospheric methane removal is under consideration as a pathway to limit near-term warming (IGSD 2023). Methane is found at low concentrations in the atmosphere (approximately 2 parts per million), however, making methane removal a challenging prospect (Abernethy and Jackson 2024). Pathways for atmospheric methane removal include open-system approaches that would modify the atmosphere or ecosystems (e.g., atmospheric oxidation enhancement (also called enhanced atmospheric methane oxidation), methane oxidizing coatings for surfaces, and terrestrial methanotrophy enhancement), and closed-system approaches using methane oxidizing reactors (Abernethy and Jackson 2024). See Mundra and Lockley (2024) for a review of some potential approaches for methane removal. For a deep exploration of methane removal see Spark Climate Solutions’ Atmospheric Methane Primer and NASEM’s A Research Agenda Toward Atmospheric Methane Removal (NASEM 2024).

Description of what it does mechanistically

• Methane removal acts by breaking down, or oxidizing, methane in the atmosphere by augmenting methane’s natural removal processes (Spark Climate Solutions 2024). Oxidation of methane produces carbon dioxide, water, and other byproducts (Spark Climate Solutions 2024). Biological methods of methane removal produce biomass (Spark Climate Solutions 2024).

Spatial extent (size)

• Unknown and will depend on approach
  • Closed-system approaches will likely have a smaller spatial extent than open-system approaches.

Where applied – vertically

• Varies by approach. Some would happen in the atmosphere and others would happen at the Earth’s surface (through biological or mechanical systems).

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

• Global application
  • Methane is well-mixed in the atmosphere, and therefore, methane removal could happen outside of the Arctic and still make a difference in the Arctic.

When effective (summer, winter, all year)

• All year

Impact on

Albedo

• Potential for increased albedo as side effect of some methods, such as dispersing aerosols in atmosphere (Oeste et al. 2017).

Temperature

• Global
  • Decrease of 0.02°C – 0.48°C
    • Removing approximately 3 years of methane emissions would decrease temperatures 0.21°C (Abernethy et al. 2021).
    • Continuous removal of 10 Mt of methane per year would decrease temperatures 0.02°C (Spark Climate Solutions 2024).
    • Modeling study reports 0.4°C temperature decrease by 2050 with 40% reduction in methane by 2050 (Abernethy et al. 2021).
    • Oxidizing all anthropogenic methane emissions would lead to an average decrease in temperature of 0.48°C (Abernethy et al. 2023).
    • Impacts on global temperature would be dependent on future potential scale of approaches and research and development efforts.
    • One group, AMR (2024), estimated a reduction of 0.5°C over approximately 20 years by reducing methane concentrations from 1.9 to 0.7 ppm via deployment of ferric chloride particles from 40-60 planes. 
• Arctic region
  • Unknown

Radiation budget

• Global
  • Unknown
    • While the intention of methane removal is to reduce retention of out-going long-wavelength radiation, uncertainties related to net efficiency and side effects prevent any accurate estimate of the ultimate impacts.
• Arctic region
  • Unknown

Sea ice

• Direct or indirect impact on sea ice?
  • Indirect via decreases in greenhouse gas concentrations and subsequent decreases in warming.
• New or old ice?
  • Both
• Impact on sea ice
  • Unknown

Scalability

Spatial scalability

• Unknown
  • Varies across approaches with some for potential to removal >10 Mt CH₄/yr (0.01 Gt CH₄/yr) and others with more limited potential <1 Mt CH₄/yr (0.001 Gt CH₄/yr) (Spark Climate Solutions 2024, note that these are early estimates). The spatial area required achieve this potential is unknown.

Efficiency

• Unknown
  • See theoretical estimations by Jackson et al. 2021.

Timeline to scalability

• Varies across approaches, however some could potentially scale within 10 years (Spark Climate Solutions 2024).

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

• Possible for approaches with potential to scale in <10 years.

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

• Possible for approaches with potential to scale in <10 years.

Cost

Economic cost

• Up to $3 billion for 20 years
  • One group, AMR (2024), estimates a cost of $1.75-3 billion for startup and deployment of enhanced atmospheric methane oxidation for 20 years.
  • Depends on further approach development and evaluation.
  • Spark Climate Solutions (2024) defines an approach as cost-effective “if the social benefit of the removed methane, and the net of all other effects, is greater than the economic social cost incurred.” Iron salt aerosols, a type of atmospheric oxidation enhancement, are identified as being potentially cost-plausible. Other techniques require increases in catalytic efficiency and other areas.

CO₂ footprint

• Unknown

TRL

• 1-3 – Theoretical and laboratory studies have been done.
  • See Mundra and Lockley (2024) for a review of readiness of some approaches. 
• Summary of existing literature and studies
  • Laboratory studies and active research summarized in Patel 2024.
  • Catalytic systems are likely to involve technology already being developed for environments with high methane concentrations (Zaelke et al. 2023).
  • Research agenda proposed in Jackson et al. 2021.
  • US National Academies of Science Engineering and Medicine has an active panel titled, “Atmospheric Methane Removal: Development of a Research Agenda”.
  • See summaries of approaches provided in Spark Climate Solutions’ Atmospheric Methane Primer.

Technical feasibility within 10 yrs

• Feasible for some approaches.
  • Will depend on research and development; see Spark Climate Solutions’ Atmospheric Methane Primer.

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.

Co-benefits and risks of methane removal are largely unknown and will vary by approach. For a summary of health and ecosystem impacts, concerns, and uncertainties for particularly approaches see Spark Climate Solutions’ Atmospheric Methane Primer.

Physical and chemical changes

• Co-benefits
  • Changes in air quality (Jackson et al. 2021); unknown if this impact will be improved or diminished air quality (S. Abernethy pers. comm.).
• Risks
  • Open-system approaches have higher risks of unintended consequences than closed-system approaches (Abernethy and Jackson 2024).
  • Changes in air quality (Jackson et al. 2021); unknown if this impact will be improved or diminished air quality (S. Abernethy pers. comm.).

Impacts on species

• Co-benefits
  • Unknown
• Risks
  • Open-system approaches have higher risks of unintended consequences than closed-system approaches (Abernethy and Jackson 2024).

Impacts on ecosystems

• Co-benefits
  • Increased primary productivity via reduced ozone levels (Jackson et al. 2021).
• Risks
  • Open-system approaches have higher risks of unintended consequences than closed-system approaches (Abernethy and Jackson 2024).

Impacts on society

• Co-benefits
  • Methane removal efforts could share infrastructure with carbon removal projects (Zaelke et al. 2023).
  • Improved air quality with benefits to human health (Jackson et al. 2021).
  • Increased crop yields due to reduced ozone levels (Jackson et al. 2021).
• Risks
  • Open-system approaches have higher risks of unintended consequences than closed-system approaches (Abernethy and Jackson 2024).

Ease of reversibility

• Not reversible
  • Methane is irreversibly destroyed in these removal approaches, therefore reversing the impact is not possible.
  • Significant amount of infrastructure may be required.

Risk of termination shock

• Low
  • Methane is destroyed in methane removal approaches. However, cessation of methane removal activities would immediately increase the net flux of methane to the atmosphere, which would increase the impact of this potent, short-lived climate pollutant.

International vs national jurisdiction

• Likely national jurisdiction, but some atmospheric approaches could be international jurisdiction.

Existing governance

• There are no international or national laws or regulations designed specifically for methane removal. See methane emissions reductions section for further information on methane. Note the recent paper from Columbia Law School’s Sabin Center for Climate Change Law which explores the international and U.S. laws governing methane removal via atmospheric oxidation enhancement (Webb et al. 2024).
• 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).

Justice

• 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.
• Distributive justice
  • Unknown
    • Funding on methane reductions and removals is currently 1% of funding from international climate finance (Abernethy and Jackson 2024).
    • If distributive justice is considered, the objective would be that the benefits and costs of research or potential deployment of the approach be distributed fairly while protecting the basic rights of the most vulnerable.
• Procedural justice
  • Unknown
    • 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.
    • 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 Indigenous self-determination and procedural justice (Chuffart et al. 2023). Note, however, that stakeholders may also include non-local people.
• Restorative justice
  • Unknown
    • If restorative justice is considered, plans would be developed for those who could be harmed by the approach to be compensated, rehabilitated, or restored.

Public engagement and perception

• This is an emerging field with limited information in the public sphere, although attention is growing.
• Stakeholders will need to be informed of tradeoffs and the relative risks of action and inaction (Abernethy and Jackson 2024).
• There is an effort in progress by the United States’ National Academies of Science Engineering and Medicine to develop a research agenda for atmospheric methane removal.
• Public support will require coordinated research, governance, and stakeholder engagement (Abernethy and Jackson 2024).

Engagement with Indigenous communities

• Unknown