Methane has basically 3 potential pathways for removal. Rapid oxidation, slow oxidation, biotic oxidation.
Rapid oxidation is burning. Methane is essentially Natural gas and vice versa and will burn if exposed to an ignition source and concentrated enough.
Slow oxidation can be highly simplified into: Oxidation of methane ——> formaldehyde ——> carbon monoxide ——> carbon dioxide. [
1] Sunlight triggers this reaction.
Biotic oxidation is accomplished by methanotrophs which are bacteria that eat methane as their only source of carbon and energy, which is then incorporated into organic compounds via the serine pathway or the ribulose monophosphate pathway. [
2] Of all the natural methane sources and sinks, the biotic oxidation is the most responsive to variation in human activities. [
3] It can be improved by proper management of upland oxic soils by proper grassland/savanna/open woodland management in agriculture. Essentially the healthy grassland soils are an overall net sink for methane, while closed canopy forests, wetlands, and degraded soils are generally not. [
4]
So to lower atmospheric methane:
1) Reduce the leakage of Natural gas from wells and pipelines and inefficient incomplete burning. Collect the methane from landfills and other manmade concentrated sources, so it can be burned as an energy source. (rapid oxidation)
2) Change agricultural production methods to take advantage of biotic oxidation. Agriculture as it is most widely practised now is both reducing the natural processes that remove methane, and in some cases increasing methane emissions. So the net component of increasing atmospheric methane that agriculture is responsible for is dramatically rising due to the effect agriculture has on both sides of the methane cycle.
You asked how can we “remove” methane? Well starting with wetlands emissions, the primary agricultural component to that portion of the methane cycle is paddy rice production. So in the case of rice, a shift to SRI would be a significant improvement.
• Reduced greenhouse gas (GHG) emissions from paddy soils
o Methane (CH4) is reduced by between 22%
and 64%, as soils are maintained under mostly
aerobic conditions [10,11,3]
o Nitrous oxide (N2O) is only slightly increased
or sometimes reduced as use of N fertilizers is
reduced; N20 increases do not offset CH4
reductions, so GWP is reduced [9,10,11,12]
oTotal global warming potential (GWP) from
flooded rice paddies is reduced 20-30%
[10,12,3], even up to 73% [11]
The System of Rice Intensification (SRI)… … is climate-smart rice production
SRI has over 700 published journal articles which can be found here:
JOURNAL ARTICLES ABOUT THE SYSTEM OF RICE INTENSIFICATION (SRI)
Please note that yields per hectare are increased at the same time as the methane is reduced. You will also find that many of the outliers mentioned in the above quote are also the same outliers in yields too. In other words, the farmers that reduce emissions the most are also the same farmers yielding the most. (and the farmers sequestering the most carbon in the soil) And the farmers producing the record yields have little to no impact on AGW any longer at all. It can not be emphasized enough how important this breakthrough is, as the methane signature from rice cultivation goes back thousands of years according to the
Ruddiman Early Anthropocene Hypothesis .
The next biggest agricultural component to methane increases is related to the way we currently practice animal husbandry. This component is primarily driven by reducing the natural processes that remove methane from the atmosphere. Since ruminants and other animals have been passing gas since the beginning of time, it is less an emissions problem but rather a symptom of soil degradation caused by the way we currently raise grains (largely to feed animals in confinement).
In my opinion methane is an animal husbandry problem primarily because of CAFO's. It is not a problem in a properly managed grassland/savanna biome. After all those biomes supported many millions and millions of grazers who were extirpated. The methane levels before they were extirpated were actually lower than now! According to the following studies those biomes actually reduce atmospheric methane due to the action of Methanotrophic microorganisms that use methane as their only source of energy and carbon. Even more carbon being pumped into the soil! Nitrogen too, as they are also free living nitrogen fixers.
Grasslands and their soils can be considered sinks for atmospheric CO2, CH4, and water vapor, and their Cenozoic evolution a contribution to long-term global climatic cooling.
Cenozoic Expansion of Grasslands and Climatic Cooling
The subsurface location of methanotrophs means that energy
requirements for maintenance and growth are obtained from
CH4 concentrations that are lower than atmospheric.
Soil Microorganisms as Controllers of Atmospheric Trace Gases
(H2, CO, CH4, OCS, N2O, and NO)
Upland (i.e., well-drained, oxic) soils are a net sink for atmospheric methane; as methane diffuses from the atmosphere into these soils, methane consuming (i.e., methanotrophic) bacteria oxidize it.
IMPACT OF METHANOTROPH ECOLOGY ON UPLAND METHANE BIOGEOCHEMISTRY IN GRASSLAND SOILS
Nevertheless, no CH4 was released when soil surface CH4 fluxes were measured simultaneously. The results thus demonstrate the high CH4 oxidation potential of the thin aerobic topsoil horizon in a non-aquatic ecosystem.
Methane fluxes from differentially managed grassland study plots: the important role of CH4 oxidation in grassland with a high potential for CH4 production.
Of all the CH4 sources and sinks, the biotic sink strength is the most responsive to variation in human activities.
Environmental impacts on the diversity of methane-cycling microbes and their resultant function
The CH4 uptake rate was only 20% of that in the woodland in an adjacent area that had been uncultivated for the same period but kept as rough grassland by the annual removal of trees and shrubs and, since 1960, grazed during the summer by sheep. It is suggested that the continuous input of urea through animal excreta was mainly responsible for this difference. Another undisturbed woodland area with an acidic soil reaction (pH 4.1) did not oxidize any CH4.
Methane oxidation in soil as affected by land use, soil pH and N fertilization
I pulled a few quotes out to make my case, but I highly recommend you read the sources in their entirety and even find further educational materials, since this is a highly complex subject.
The main summary being, the current system used to raise animals in confinement has removed them from the farmland, where when managed properly their methane emissions are part of a larger agricultural system that oxidizes more methane than the animals emit. Since this biological oxidation of methane occurs below the soil surface where that carbon enters the soil food web, actually animals improve the BCCS systems even more than without them. This actually has been known for decades and is well vetted, but was never quantified for climate scientists. Sir Albert Howard, father of organic agriculture, noted this effect on soil biology (of removing farm animals from the land and replacing their impact with synthetic fertilizers) way back in the 1940s.
“As the small trickle of results grows into an avalanche — as is now happening overseas — it will soon be realized that the animal is our farming partner and no practice and no knowledge which ignores this fact will contribute anything to human welfare or indeed will have any chance either of usefulness or of survival.”
Sir Albert Howard
In my honest opinion one reason for the recent spike in atmospheric methane is simply the fruition of Sir Albert Howard's prediction, since we continue to ignore this. Loss of soil carbon would be another impact of ignoring this.
The third major factor in increased emissions is from natural wetlands. I am less familiar with this portion of the methane cycle, but I can hypothesize that it could potentially be related in part to agricultural runoff causing anaerobic conditions (dead zones), since most decomposition under anaerobic conditions does produce large quantities of methane.
Fertilizer Runoff Overwhelms Streams and Rivers--Creating Vast "Dead Zones" Ironically the "King Corn" lobby is so huge, that even though the above article from Scientific America admits the primary cause cropland runoff of synthetic nitrogen, they actually propose:
the only way to increase ethanol production from corn and reduce nitrogen runoff would be for Americans to stop eating meat, thereby freeing up corn used as livestock feed for other uses.
While also stating:
"That [also] means not utilizing all the land to grow crops."
Apparently they don't see the irony in these two statements. The solution of course is not to grow corn for ruminants at all and dramatically reduce its usage for other livestock. And not to use corn for ethanol production at all. (excepting a nice corn whiskey) There are other ways to feed animals and distill ethanol more efficiently than using "king corn" surpluses.
Grass Makes Better Ethanol than Corn Does
Soil Carbon Storage by Switchgrass Grown for Bioenergy
So step one is to stop subsidizing the over production of corn and soy and changing our production models to more efficient regenerative models of production that don't cause AGW. And ironically instead of agriculture contributing to the methane problem, we could use it to more rapidly oxidize methane coming from other sources too!
3) Whatever gets past the first two measures will be slow oxidized. It is about 10+/-years 1/2 life for this reaction.
