Determining whether a potential atmospheric methane removal approach is high-quality requires evaluating it on a number of criteria. At this early research stage, Spark is focused on encouraging solution development towards building a portfolio of methods that could have sufficient scale for meaningful climate impact, are cost-effective and climate-beneficial, and could earn widespread social acceptance at the time and location of potential future considered deployments.
To achieve these goals, we consider the following factors.
Feasible approaches have a viable path to being, at some scale:
How much, and how quickly, each approach could scale is also highly relevant to overall potential climate impact — the higher the scale, and the faster to potential scale, the larger of an impact the approach can have. There could be 100+ million metric tons of additional methane emitted annually from elevated natural sources by 2100 that might be addressable by atmospheric methane removal approaches, depending on how they develop.
Additional principles and factors will be important for any field testing or deployment of atmospheric methane removal, including governance, social acceptance, local engagement, environmental and climate justice, verifiability, and additionality. As the field progresses from early research stages to potential future deployments, further evaluation criteria will also need to be established, similar to the high-quality criteria for carbon dioxide removal.
An atmospheric methane removal approach is climate beneficial if its positive climate benefits outweigh its negative climate impacts.
We use the 20 year Global Warming Potential (GWP20) in our evaluation of the climate impact of methane removal approaches to align with the intended role of methane removal in addressing near-term warming. This analysis is preliminary, and complete analysis of methane removal approaches should evaluate robustly across time and space scales. Approaches which may be climate positive globally or in the near-term may have detrimental regional or long-term impacts that need to be considered.
Negative climate impacts may come from greenhouse gas emissions, like carbon dioxide and nitrous oxide, produced during the lifecycle of the atmospheric methane removal approach. Or they may be less obvious. For example, a proposed methane removal approach may alter the Earth’s albedo or change the ability of the atmosphere to oxidize greenhouse gasses. As these effects may vary in intensity over time, life cycle analyses of climate impacts will have to be evaluated over time, considering both near-term and long-term impacts.
We describe an atmospheric methane removal 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. In addition to global analyses, local analyses of those most impacted (likely near deployment sites) are critically important to not saddle frontline communities with additional risks and harms. Given the early state of research across all methods, we currently evaluate these on an estimated technoeconomic cost basis to identify key development areas that could enable approaches to become cost-effective in the future. This will need much more detailed followup work as more information becomes available about different types of costs incurred by each method to better understand non-economic costs and their distribution. This is further covered in the “Harms and Benefits'' section below.
The social cost of methane emitted is estimated to be roughly $2,000 USD per metric ton of methane by 2030. However, the social benefit of oxidizing methane may be higher or lower than that depending on the approach. Some approaches fail to address the additional effects of emitted methane, like the air quality impacts of increased ozone, while others may result in the oxidation of additional pollutants. Acknowledging this uncertainty, we estimate the threshold for cost-effective approaches at around $2,000 per metric ton of methane, though this will depend on the approach and may evolve as we learn more.
The social cost of methane may rise as we gain a greater understanding of the risks of methane and near-term warming more generally on society and the Earth system, and it will certainly rise in future scenarios in which global temperatures and atmospheric methane levels are higher. Therefore, we articulate a second threshold for cost considerations: cost-plausible, where the projected cost has a viable path to being under the projected social cost of methane in a high emissions, high climate feedback scenario. With very low confidence, we believe it’s conceivable in the future for this value to rise as high as $10,000 per metric ton of methane.
Above this threshold we currently consider a solution to be cost-implausible.
Some potential atmospheric methane removal approaches impact the climate in many ways beyond only methane removed. In these cases, it’s crucial to look at the entire climate effect, and evaluate costs compared to the net climate effect, rather than only evaluating the approach’s impact on methane, which may dramatically under or overestimate the overall climate impact.
Atmospheric methane removal approaches may cause other harms and benefits beyond their climate impact, be that related to social, environmental, health, or other factors. Potential examples include changes to air quality, impacts on soil health, and local economic impacts, for example through job creation. These impacts are often influenced by both the approach itself and the specifics of a potential deployment, including the location and existing environmental conditions.
An integral part of developing any atmospheric methane removal approach is understanding the potential harms and benefits inherent to the approach. As approaches later may shift to deployment considerations, this information will be crucial in helping to support informed decision-making, and additional project specific considerations will also need to be added.
Given the early research state of each approach, our current analysis focuses on building knowledge of what these harms and benefits might be for each approach, and how to support approach development to minimize harms and maximize benefits. Social license, good governance (see below for more), and thorough research and modeling will be required to inform any potential future deployment decisions.
The potential scale of each approach currently being researched is not yet well-known, but can be roughly estimated based on underlying supply chain, physical, and biological factors. Approaches of every scale have a role in addressing atmospheric methane levels. There could be 100+ megatons of methane emitted annually from elevated natural sources by 2100, which might be addressable by atmospheric methane removal approaches depending on how they develop.
It’s helpful to have a few benchmarks to talk about various potential scales of approaches:
Timelines and goals also depend on changes in the soil and atmospheric oxidative sink due to land use changes, pollution controls, and decarbonization. More research is needed to understand the direction and magnitude of changes in the total methane sink over the coming decades, considering all potential direct and indirect effects. We also expect that better measurement and modeling will improve predictions for increases in wetland and permafrost methane emissions.
A portfolio of approaches is likely to be necessary to achieve the total desired scale. Having a diverse portfolio can also help to reduce the risks that any specific approach ends up proving nonviable. The scale that an approach can reach will depend on social license and labor, land, and raw material resource constraints, as well as fundamental constraints imposed by the Earth system.
The faster that a potential atmospheric methane removal approach would be able to scale, the more of an impact it can have on near-term warming, and in reduction of potential overshoot scenarios.
To play a role in peak-shaving in 1.5C scenarios with overshoot, and help to achieve Paris Agreement goals, an atmospheric methane removal approach would need to be able to scale in the next 10 to 20 years, in parallel with aggressive overall greenhouse gas emissions reduction and carbon dioxide removal scale-up.
However, unmitigated methane risks are also long-term and ongoing risks, which will continue to evolve as our overall future climate trajectory does. Approaches that can be scaled on later timelines remain potentially crucial additional tools to manage a number of climate system risks. The warmer our overall climate trajectory, the higher the risk of climate tipping elements and other severe climate impacts, and the more acute methane-emitting natural feedbacks are expected to be, further driving both the potential scale for atmospheric methane removal solutions, as well as their incremental value, given the accelerating global costs of higher warming scenarios.
Social license to operate will have to be earned for atmospheric methane removal approaches to be deployed and scaled. Beyond the technical considerations listed above, social acceptance, verifiability, and additionality of positive impacts, equity in how they are distributed, diversity and inclusion of affected voices and interests, and effective governance will be critical requirements for field testing or deployment of atmospheric methane removal. They’re all prerequisites for earning social license to operate.
Diversity, equity and inclusion are foundational principles for any climate intervention. Diversity and inclusion require welcoming diverse approaches and listening to diverse actors, voices, and needs. Equity starts with a recognition that the environmental and social injustices of climate change and polluting industries have been and are still disproportionately borne by historically marginalized communities.
Another foundational principle for research, development and any field testing or deployment of a climate solution is free, prior, informed consent by affected communities. Indigenous communities in particular have the right to such consent enshrined in international law, but it’s a human right which applies to all affected communities. Any field testing, or deployment of a proposed solution must be supported by rigorous research into social and environmental impacts, and social acceptance of those impacts by affected communities. Effective governance needs to prioritize the public interest and ensure transparency and accountability. Such governance is necessary for the healthy development and consideration of atmospheric methane removal approaches, and must be in place at the relevant regional scale (be that subnational, national, or international, dependent on the scope of impact of a given approach and the potential action) prior to any field testing or deployment.
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