Methane is a powerful, short-lived greenhouse gas that has caused about a third of global warming to date (IPCC AR6 2021). As global temperatures increase, several natural systems risk passing tipping points with global, societally destabilizing consequences (Armstrong McKay et al. 2022). Because of methane’s potency and fast-acting warming effect, methane mitigation—encompassing both emissions reduction and removal—has a high potential impact to lower peak warming when paired with achieving net-zero, and then net-negative, CO₂ emissions. While technical solutions exist for the majority of anthropogenic methane emissions, and these should be deployed rapidly, significant additional research and innovation is required to develop additional mitigation options, across emissions reduction, point-source methane removal, and atmospheric methane removal. Atmospheric methane removal methods, if developed, would play an important and unique role by being able to accelerate the removal of historical and rising natural emissions as well.

Methane has always been emitted from wetlands, termites, and other natural sources. However, anthropogenic emissions have more than doubled natural methane emissions, placing the earth’s climate at risk (Saunois et al. 2020). Moreover, evidence is emerging that even “natural emissions” from wetlands are starting to increase as a result of human-caused warming. 

Methane is relatively short-lived in the atmosphere, as atmospheric methane is converted (“oxidized”) to CO₂ and water over an average of a decade, primarily by natural chemical detergents in the air and by soil bacteria. The conversion of methane to CO₂ has a beneficial climate impact, as a methane molecule is 43x stronger at warming the Earth than a molecule of CO₂ (IPCC AR6 WG1 Chap 7 Table 7.15). Historically, annual methane emissions roughly balanced natural methane destruction and atmospheric methane levels remained stable. Today, elevated methane emissions as a result of human activities are causing methane to be added to the atmosphere faster than natural destruction of methane can remove it (Jackson et al. 2020). So far, methane levels in the atmosphere have more than doubled since pre-industrial times, and are now rising at record rates (NOAA Press Release 2022). 

Restoring methane to preindustrial levels would decrease warming by around 0.5°C compared to today (Abernethy and Jackson 2021); methane mitigation is thereby essential to minimize temperature overshoot, but safe temperatures can only be achieved if CO₂ and other greenhouse gas emissions also hit net-zero, and our carbon budget is not exceeded. Methane and other short-lived climate pollutants play a different role in warming than CO₂ and other long-lived climate pollutants, and should not be treated interchangeably in any policy context (Allen et al. 2022). Because methane warms so powerfully for the decade it is in the atmosphere, it has a particularly strong influence on near-term warming. In contrast, CO₂ persists in the atmosphere for centuries, cumulatively driving long-term warming. To stop the upward march of CO₂-driven warming, and the resulting crossing of tipping points, CO₂ emissions must be reduced and eventually CO₂ levels stabilized to safe levels via atmospheric removal (called carbon dioxide removal, or CDR). Significant atmospheric methane reduction (through methane emissions destruction and possibly atmospheric removal) alongside fast restoration of safer CO₂ levels through both CO₂ emissions reduction and carbon dioxide removal—jointly achieving net-negative emissions—and similar treatment of other greenhouse gasses would limit peak temperatures, is an important part of every low-1.5°C-overshoot-consistent scenario, and would minimize the length of time above 1.5°C warming (Dreyfus et al. 2022). All of these benefits would decrease the risk of natural feedbacks and tipping points that accelerate warming before atmospheric CO₂ can be restored to safe levels (Armstrong McKay et al. 2022). If methane-emitting natural sources accelerate (as they are predicted to), large-scale atmospheric methane removal, if developed, could help reduce the negative impacts and slow or prevent feedback loops.

To realize the potential of methane mitigation to shave peak warming substantially, in addition to deploying known approaches to methane emissions reduction, the world needs to develop new approaches to both reduce methane emissions and remove legacy methane from the atmosphere, fast.

Humans now cause around 60% of annual methane emissions, primarily from livestock belches, extraction and distribution of all fossil fuels, manure management, rice growing, landfills, and wastewater treatment (IEA Methane Tracker, 2021). While viable methods for reducing methane emissions from most of these sources are known today, only an estimated 57% of projected 2030 human-caused methane emissions can be eliminated with current technical solutions, even if cost wasn’t a factor (Ocko et al 2021). In addition, current proposals to prevent or remove natural methane emissions, which have increased as warming has progressed, are speculative and untested.

It is therefore critical that there be support for research into new methods to avoid methane emissions (including methane emissions destruction or utilization) as well as methods for atmospheric methane removal (Jackson et al. 2021, Ming et al. 2022). Methods for methane emissions destruction or utilization that could operate at low-concentrations and atmospheric methane removal are particularly early-stage and underfunded. While high-concentration concentrated sources of methane can be partially destroyed by flaring, a majority of remaining sources emit methane at concentrations below the levels that can be combusted. Methods are being researched that might apply to point sources with medium methane concentrations (e.g., a coal mine ventilation shaft), area sources with low methane concentrations (e.g., the area above a rice paddy), or the open atmosphere where methane concentrations are very low, currently around 2 ppm. Proposals usually involve catalysts, oxidizing radicals, or methane-consuming organisms, which may be in controlled environments, on building surfaces, or in soil, water, or air.

Some of these proposed methods, if proven and scaled, could be game-changers in terms of peak warming – potentially reducing peak temperature by multiple tenths of a degree Celsius (Abernethy and Jackson 2021). But these methods are underexplored, with copious unanswered scientific questions. Concerted funding and validation for methane removal approaches are needed to provide the world a set of tools that could, if deployed in parallel and in addition to rapid CO₂ cuts, minimize 1.5°C overshoot.

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¹ Abrupt thaw of permafrost, which may occur between 1.0 and 2.3°C of warming, may result in an increase of 0.2°C over 100-300 years, while collapse of the permafrost, which may occur at between 3 and 6°C global average warming or ~9°C regional average warming, may result in an increase of 0.3-0.4°C additional warming over 25 to 100 years (Armstrong McKay et al. 2022).  

² Unfortunately, recent studies have found that many combustion sources still emit significant quantities of uncombusted methane. Flaring technology must also be improved.

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