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.

• Methane (CH₄) is the second most important anthropogenic greenhouse gas after CO₂ and is responsible for about 30% of global mean temperature increase since the Industrial Revolution (AMAP 2021 full report, IPCC 2021, IEA 2024). Reductions in methane emissions would be effective for short-term cooling of the Earth, as methane is a short-lived constituent of the atmosphere. Methane is also well-mixed in the atmosphere, and therefore, methane emissions reductions could happen outside of the Arctic and still make a difference in the Arctic. There is high confidence by the IPCC (2021) that “strong, rapid and sustained reductions in methane emissions can limit near-term warming and improve air quality by reducing global surface ozone”.
• Pathways to reduce methane emissions include 1) strengthening methane mitigation policies, 2) reducing leaks and venting in the oil and gas sector, 3) eliminating flaring from oil and gas operations, 4) reducing enteric methane by improving feeding and manure management on farms or other methods, 5) eliminating gas in new construction and phasing out leaky gas stoves, 6) upgrading solid waste and wastewater treatment, and 7) reducing food waste and improving landfill management (Zaelke et al. 2023).
  • The energy sector accounts for about 35% of anthropogenic methane emissions and has the largest potential for abatement in the immediate decades (UNEP and Climate and Clean Air Coalition 2021).
  • The International Energy Association’s Net Zero Emissions by 2050 (NZE) Scenario that limits the global average surface temperature rise to 1.5 °C with no or low overshoot includes a 75% cut in methane emissions from fossil fuel production and use by 2030 (IEA 2024).
• See UNEP and Climate and Clean Air Coalition 2021, 2022, IGSD 2023, IEA 2024, and Mundra and Lockley 2024 for more detailed information about methane emissions reductions pathways.

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

• Methane emissions reduction approaches either emit zero methane emissions or lower current methane emissions. By implementing these technologies, methane emissions will decrease, thereby slowing increases in global mean surface temperature.

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

• Varies by approach, but likely small spatial footprint
  • Many approaches will have a small spatial footprint and rely on existing infrastructure.

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.

• Mostly on land surface

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.

• Global application
  • Methane is generally well-mixed in the atmosphere, and therefore, methane emissions reductions could happen outside of the Arctic and still make a difference in the Arctic. Methane concentrations are higher in the Northern Hemisphere, although the mechanisms are unclear (Nisbet et al. 2021).

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

• All year

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.

• Unknown

Temperature

• Global A description of the approach’s potential impact on global mean surface temperature (°C).
  • Decrease of 0.28°C to 0.5°C or greater, compared to trajectory with no targeted methane mitigation.
    • Temperature decrease of 0.28°C in 2040s with 0.32°C decrease by 2050 (UNEP and Climate and Clean Air Coalition 2021), > 0.5°C by 2100 (Dreyfus et al. 2022).
    • Successful implementation of the Global Methane Pledge would reduce warming by at least 0.2°C by 2050 (Joint US-EU Statement on the Global Methane Pledge, cited by Zaelke et al. 2023).
    • Model simulations show that combining targeted mitigation strategies of methane and black carbon with decarbonization keeps warming below 2.0°C (Dreyfus et al. 2022).
• Arctic region A description of the approach’s potential impact on temperature within the Arctic region (°C).
  • Decrease up to 0.5°C by 2050 compared to trajectory with no targeted methane mitigation.
    • Decrease in Arctic of 0.5°C by 2050 (0.3°C by 2040s; UNEP and Climate and Clean Air Coalition 2021) if cut emissions by 40-45% by 2030.
    • Mitigating short lived climate pollutants, including methane, in addition to decarbonization would reduce the rate of Arctic warming by 2/3 (Zaelke et al. 2023).
    • Maximum feasible reductions of global methane emissions from anthropogenic sources could lead to a reduction in the warming rate of 0.047°C per decade from 2015-2050 relative to current emissions (AMAP 2021). Corresponding temperature decrease of 0.035°C by 2030, 0.164°C by 2050 (AMAP 2021 full report).

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).
  • Unknown
• 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 decreases in greenhouse gas concentrations and subsequent decreases in warming.
• 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.
  • Reduced risk of losing Arctic summer sea ice (Sun et al. 2022).

Scalability

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

• Many approaches will have a small spatial footprint and rely on existing infrastructure and operational footprints.

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

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

• < 10 years
  • 45% of anthropogenic methane emissions from energy production, agriculture, and waste could be cut by 2030 with existing technology (IGSD 2023).

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.

• Possible within 20 years
  • Methane emissions reductions estimated to have impact within a decade (UNEP and Climate and Clean Air Coalition 2021).
  • Methane emissions reductions is likely the fastest strategy for temperature reductions (UNEP and Climate and Clean Air Coalition 2021, IGSD 2023).

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.

• Possible within 20 years
  • Methane emissions reductions estimated to have impact within a decade (UNEP and Climate and Clean Air Coalition 2021).

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).

• About 60% of available targeted measures have mitigation costs less than US $21 per tonne of carbon dioxide equivalent (CO₂e) for GWP₁₀₀ and less than US $7 per tonne of CO₂e for GWP₂₀. Just over 50% of those have negative costs (UNEP and Climate and Clean Air Coalition 2021 in Zaelke et al. 2023).
• For about 85% of approaches for methane emissions reductions the benefits outweigh the costs (UNEP and Climate and Clean Air Coalition 2022).
• “Cutting methane emissions from the energy sector by 75% by 2030 is one of the least cost opportunities to limit global warming in the near term” (IEA 2023).
  • Estimated costs for cutting methane by 75% from oil and gas operations is $75 billion USD (2% of net income from the oil and gas industry in 2022; IEA 2023).

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

TRL Technology readiness level as defined by the National Oceanic and Atmospheric Administration (https://orta.research.noaa.gov/support/readiness-levels/).

• Varies depending on technology, but many are 9.
  • See Ocko et al. (2021) for detailed information on readiness across sectors and Mundra and Lockley (2024) for a review of readiness of many approaches.
• Summary of existing literature and studies
  • 57% of methane emissions are technically feasible to mitigate today, yet only 24% of emissions mitigation are economically feasible with no net cost (Ocko et al. 2021).
  • Implementation of existing technologies could cut 45% of anthropogenic methane emissions by 2030 from energy production, agriculture, and waste (UNEP and Climate and Clean Air Coalition 2021).
  • Methane emissions monitoring systems exist and are under development, although more are needed. For a summary of methane measurement and monitoring initiatives see IGSD 2023.

Technology feasibility within 10 years Estimation of whether this approach could be technically feasible (i.e., a demonstration project would be possible) within 10 years based on best available knowledge. Technical feasibility does not imply scalability.

• Feasible
  • Many approaches are feasible, while some need major innovation.

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.

Physical and chemical changes

• Co-benefits Potential beneficial impacts to the physical or chemical domain due to application of the approach.
  • Reducing methane also reduces tropospheric ozone levels (Zaelke et al. 2023).
  • Stopping methane leaks from oil and gas reduces non-methane precursors (Zaelke et al. 2023).
  • Improved air quality (Zaelke et al. 2023).
• Risks Potential negative impacts to the physical or chemical domain due to application of the approach.
  • Unknown

Impacts on species

• Co-benefits Potential beneficial impacts to species due to application of the approach.
  • Unknown
• Risks Potential negative impacts to species due to application of the approach.
  • Unknown

Impacts on ecosystems

• Co-benefits Potential beneficial impacts to ecosystems due to application of the approach.
  • Unknown
• Risks Potential negative impacts to ecosystems due to application of the approach.
  • Unknown

Impacts on society

• Co-benefits Potential beneficial impacts to society (human communities) due to application of the approach.
  • Improved air quality (IEA 2023, Zaelke et al. 2023).
    • Reducing methane emissions would prevent approximately 200,000 premature ozone-related deaths (UNEP and Climate and Clean Air Coalition 2022, cited in Zaelke et al. 2023).
    • Reducing methane emissions would avoid approximately $500 billion per year expenses due to non-mortality health impacts (UNEP and Climate and Clean Air Coalition 2022).
  • Reducing methane emissions would avoid the yield loss of approximately 580 million tons of staple crops (UNEP and Climate and Clean Air Coalition 2022).
  • Avoided impacts on forestry and agriculture (UNEP and Climate and Clean Air Coalition 2022).
  • Job creation (IGSD 2023).
• Risks Potential negative impacts to society (human communities) due to application of the approach.
  • Some efforts to limit methane emissions from livestock or efforts via diet switching could have other environmental impacts (UNEP and Climate and Clean Air Coalition 2021).

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
  • Impacts of methane emissions reductions would be reversed quickly if emissions reductions measures were omitted and emissions returned.

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

• No risk
  • If emissions reductions measured were halted and emissions were allowed to rise, temperatures could increase rapidly due to the potency of methane and its short lifetime. However, this scenario seems unlikely.

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.

• National
  • Action on methane is occurring at the national and subnational level, strengthened by international pledges, such as the Global Methane Pledge.

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.

• International
  • International collaboration is critical for action on methane. For a summary of public and private international organizations and initiatives see IGSD 2023.
  • Around 150 countries have signed on to the Global Methane Pledge. This voluntary agreement has a collective goal of reducing global methane emissions by at least 30% below 2020 levels by 2030. Implementation of the pledge would decrease temperatures by at least 0.2°C by 2050. The Global Methane Pledge forms a foundation to create a global methane agreement, with the Montreal Protocol providing a framework structure and approach (IGSD 2023).
  • See IGSD 2023 for a summary of potential international governance pathways including The Global Methane Pledge and Glasgow Climate Pact, the Gothenburg Protocol to the Convention on Long-Range Transboundary Air Pollution, the US-China Joint Glasgow Declaration on Enhancing Climate Action in the 2020s, and the Montreal Protocol.
  • Action on methane is severely underfunded (IGSD 2023). The Global Methane Hub is an international coordinated approach trying to strengthen methane mitigation funding.
• Several countries have released or are building national methane action plans, and some oil and gas companies have also set methane targets (IEA 2023). For a summary of country-specific methane mitigation measures see IGSD 2023.
• Across international and national governance mechanisms, verification of methane action is lacking (Nisbet et al. 2021).

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.

• 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 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)
  • Action on methane is severely underfunded (IGSD 2023) and funding is not distributed equally across sectors or geographies.
  • Methane monitoring systems are not distributed appropriately geographically (Nisbet et al. 2021).
• 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)
  • Opportunities for participation in governance of emissions reductions have increased over time. Localized actions can enable participation but can be limited by resource and capacity constraints (IPCC 2022).
  • Each individual emissions reductions pathway will have specific procedural justice concerns, which will also vary by region and country.
• 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)
  • Each individual emissions reductions pathway will have specific restorative justice concerns, which will also vary by region and country.

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.

• A 2023 public opinion poll commissioned by the Global Methane Hub conducted in 17 countries reports that 82% of respondents support methane mitigation (GMH 2024).

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.

• Unknown