How does methane removal work, and how is it different from carbon dioxide removal?

The term “methane removal” is shorthand for accelerating the natural transformation of methane in the atmosphere.  All methane in the atmosphere eventually breaks down to water vapor and CO2 through natural oxidation. Methanotrophic bacteria also breaks down methane in the biosphere.

Since current methane emissions are so high, methane is getting added to the atmosphere much faster than natural processes can break it down, so atmospheric methane concentrations are building up . In fact, they are now at record highs and have become a major factor in accelerating rates of climate change. 

Methane removal technologies would work by speeding up natural processes sufficiently to counteract high emissions levels, so that methane concentrations would fall. Scientists estimate that coupling effective methane removal technologies with aggressive cuts in methane emissions could enable us to restore atmospheric methane to preindustrial levels by 2050.  

There are some similarities, and also important differences, between methane removal and carbon dioxide removal (CDR). CDR removes CO2 from the atmosphere by enhancing biological or geochemical carbon sinks or by direct capture of CO2 from air. The captured carbon must be sequestered or stored to keep it from being reemitted.  

If removal technologies involve other GHGs besides CO2, they are considered greenhouse gas removal (GGR).   Methane removal is therefore a type of greenhouse gas removal (GGR). But unlike CDR,  methane that has undergone a removal process doesn’t need to be sequestered or stored, because it gets broken down chemically. 

For example, oxidizing methane transforms it into water vapor and CO2, which is a big net gain in terms of reduced global warming.  Ton for ton, measured instantaneously, methane is over 100 times more potent a warming agent than CO2.  Measured over 20 years, it’s over 80 times more potent.  Accelerating methane oxidation into water vapor and CO2 greatly reduces the global warming potential. 

And it’s not as if methane removal would produce any more COthan would be produced otherwise.  With or without methane removal, methane would oxidize into water vapor and CO2. The main difference between natural methane oxidation and methane removal is time:  methane removal enhances methane oxidation and speeds up the natural process, so atmospheric methane levels fall faster.

Another difference between methane removal and CDR is that some types of methane removal don’t involve filtering it out of the air.  Since the concentration of methane in the atmosphere is about 200 times lower than carbon dioxide, capturing it mechanically could prove difficult and energy-intensive.  Luckily, methane doesn’t necessarily need to be captured, since it can be oxidized freely using catalysts. 

Other types of proposed methane removal technologies could be combined with direct air capture machines or photocatalytic reactors, filtering out methane along with the greenhouse gases. They could also be applied in the open, at or near large methane emissions sources like coal mines or rice paddies, or in the ambient air.  

There are a broad range of methane removal technologies under development.  They include photocatalysts, catalysts associated with zeolites and porous polymer networks, biological methane removal such as biotrickling filters and soil management approaches, and iron salt aerosol methods or catalysts enhancing natural methane sinks which accelerate atmospheric oxidation of methane.   

Delivery mechanisms may be active or passive, ranging from catalytic coatings on vehicles, windmills, windows, and buildings, to solar updraft chimneys that move large volumes of air through passive convection, to active air moving devices and diffusion of catalysts.  Initial estimates of energy requirements for these methane removal approaches seem much smaller than for CDR.

Methane removal technologies are in various stages of development. Each needs further research on cost, technological efficiency, scaling and energy requirements, co-benefits, and impacts. Each requires appropriate governance, independent safety assessment, environmental impact assessment, and further research and development to advance toward testing and deployment. Methane Action is working on each of these fronts, and committed ensuring that any deployment of methane removal would be done in scientifically and environmentally sound, safe, and sustainable ways.  

That’s not to say we should prioritize cutting methane emissions over CO2.  We need to cut both emissions; in fact, the two are linked.  As CO2 emissions rise, and the planet warms, so do methane emissions; and reciprocally, as methane emissions rise, more CO2 is released.  So, too, as CO2 and methane are drawn out of the atmosphere, warming will decrease. So there’s a twin imperative to cut methane and CO2 emissions alike as deeply and rapidly as we can, while also investing in greenhouse gas removal technologies, including methane removal technologies.

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