There are several potential approaches to accelerate the breakdown of atmospheric methane. All of these are either in early research stages, or are ideas that haven’t received much if any research attention yet. In each case, fundamental questions remain about their feasibility, scalability, and side effects. Research funding is a bottleneck for much of the field.
Atmospheric Oxidation Enhancement (AOE) is the concept of enhancing the overall oxidative sink in the atmosphere through generating or introducing airborne materials which oxidize methane, like chlorine and hydroxyl radicals. The current pathways in early research stages are iron salt aerosols (ISA), hydrogen peroxide dispersal, and photocatalytic aerosols. Any approach proposing to alter atmospheric chemistry with the aim of oxidizing additional methane will need very careful study to understand its full atmospheric chemistry impact, including health, environmental, and climate-impact side effects. Because radicals “seek out” things to oxidize in the open air, and don’t require air-handling equipment, this category could be the fastest to scale, and potentially reach the largest overall scale. Cost plausibility depends on the specific potential pathway, and generally depends on the approach being highly catalytic. All of the potential approaches here need much more research to understand their feasibility, scalability, and what their full atmospheric impact would be. There is important supporting scientific work to pursue in parallel with any of these methods to advance our understanding of the impacts of altering oxidizing radicals in the atmosphere in general.
Terrestrial Methanotrophy Enhancement explores whether natural terrestrial or aquatic methane sinks can be safely, sustainably, and meaningfully enhanced to break down additional atmospheric methane. About 11 to 49 Mt/yr of methane is currently removed from the atmosphere by methanotrophic bacteria, most in soils. Approaches under very early exploration include soil amendments and enhanced methanotrophs. Their potential ability to address atmospheric methane at scale is currently only theoretical and this area needs much more research to understand potential pathways and their full impacts.
Methane breakdown reactors are designed to pass air from the atmosphere, either passively or actively, through catalytic systems which leverage energy from the sun, an artificial light, or heat to oxidize methane. These approaches include thermocatalysis, photocatalysis, and radicals produced artificially through photolysis (using light to break apart a molecule). These catalysts could be deployed in reactors which use fans or passive air flow to intake air from the atmosphere.
Given the low atmospheric concentration of methane, any flow through system would have to process massive amounts of air to reach high scales of methane removal. For example, if you put methane oxidizing reactors on every carbon dioxide direct air capture system that is supposed to be installed by 2030 (60 Mt CO₂/yr or around 5 billion cubic feet per minute), the reactors would only be able to remove around 0.1 Mt/yr of methane.
In addition, innovation would be needed for any of these methods to bring down air-handling costs, and some of the approaches require approach specific breakthroughs in order to make each approach cost-plausible and climate-beneficial. Methane breakdown reactors could be co-located with other climate interventions, such as carbon dioxide capture systems, to lower air-handling costs.
The approaches are already promising for breaking down methane at its emissions sources where its concentration is higher. We do not evaluate these approaches for their potential ability to do so here since our focus is on atmospheric methane concentrations.
Photocatalysts might also be deployed as a coating on panels, rooftops, or other large surfaces exposed to sunlight and air. This approach has already been investigated to improve air quality in polluted areas, but research into its potential as a methane removal approach has not yet begun.
The evaluations below are all in the context of atmospheric methane concentrations (currently ~2 ppm). Some of these same technologies could address higher concentration methane streams from various sources before the methane becomes mixed into the atmosphere. At higher methane concentrations, the evaluations for different technologies would be very different. Given the early stage of these approaches, the evaluations below are intended to motivate additional research funding, and not preclude any specific approaches from further research.
* These approaches, based on early analysis, will likely require multiple breakthroughs in order to feasibly address atmospheric methane levels. They may hold the most promise if they also deliver separate benefits (e.g. for climate or pollution), as part of systems deployed for other primary reasons, or to address low-concentration methane sources.
The continuous removal of 10 Mt of methane per year would lead to an asymptotic global cooling of 0.02°C. Over long time scales, this has approximately the same temperature impact as a one-time avoidance or removal of 37 Gt of carbon dioxide (roughly the current anthropogenic carbon dioxide emissions from a single year).
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