Methane emissions

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Sources of methane emissions due to human activity:
year 2020 estimates [1]

  Fossil Fuel Use (33%)
  Animal Agriculture (30%)
  Plant Agriculture (18%)
  Waste (15%)
  All Other (4%)

Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating.[1][2] During 2019, about 60% (360 million tons) of methane released globally was from human activities, while natural sources contributed about 40% (230 million tons).[3][4] Reducing methane emissions by capturing and utilizing the gas can produce simultaneous environmental and economic benefits.[1][5]

Since the Industrial Revolution, methane concentrations in the atmosphere have more than doubled, and about 20 percent of the warming the planet has experienced can be attributed to the gas. [6]About one-third (33%) of anthropogenic emissions are from gas release during the extraction and delivery of fossil fuels; mostly due to gas venting and gas leaks from both active fossil fuel infrastructure and orphan wells.[7] Russia is the world's top methane emitter from oil and gas.[8] Animal agriculture is a similarly large source (30%); primarily because of enteric fermentation by ruminant livestock such as cattle and sheep. According to the Global Methane Assessment published in 2021, methane emissions from livestock (including cattle) are the largest sources of agricultural emissions worldwide[9]A single cow can make up to 220 pounds of methane gas per year. [10] Methane from fossil fuels doesn't have the same characteristics as biogenetic methane (from animals). In regards to how it warms the planet up, biogenetic methane shares more traits with CO2[11]Human consumer waste flows, especially those passing through landfills and wastewater treatment, have grown to become a third major category (18%). Plant agriculture, including both food and biomass production, constitutes a fourth group (15%), with rice production being the largest single contributor.[1][12]

The world's wetlands contribute about three-quarters (75%) of the enduring natural sources of methane.[3][4] Seepages from near-surface hydrocarbon and clathrate hydrate deposits, volcanic releases, wildfires, and termite emissions account for much of the remainder.[12] Contributions from the surviving wild populations of ruminant mammals are vastly overwhelmed by those of cattle, humans, and other livestock animals.[13]

Atmospheric concentration and warming influence[edit]

Globally averaged atmospheric concentration and its annual growth rate.[14] In April 2022, NOAA reported an annual increase in global atmospheric methane of 17 parts per billion (ppb) in 2021—averaging 1,895.7 ppb in that year—the largest annual increase recorded since systematic measurements began in 1983; the increase during 2020 was 15.3 ppb, itself a record increase.[15]

The atmospheric methane (CH4) concentration is increasing and exceeded 1860 parts per billion in 2019, equal to two-and-a-half times the pre-industrial level.[16] The methane itself causes direct radiative forcing that is second only to that of carbon dioxide (CO2).[17] Due to interactions with oxygen compounds stimulated by sunlight, CH4 can also increase the atmospheric presence of shorter-lived ozone and water vapour, themselves potent warming gases: atmospheric researchers call this amplification of methane's near-term warming influence indirect radiative forcing.[18] When such interactions occur, longer-lived and less-potent CO2 is also produced. Including both the direct and indirect forcings, the increase in atmospheric methane is responsible for about one-third of near-term global heating.[1][2]

Though methane causes far more heat to be trapped than the same mass of carbon dioxide, less than half of the emitted CH4 remains in the atmosphere after a decade. On average, carbon dioxide warms for much longer, assuming no change in rates of carbon sequestration.[19][20] The global warming potential (GWP) is a way of comparing the warming due to other gases to that from carbon dioxide, over a given time period. Methane's GWP20 of 85 means that a ton of CH4 emitted into the atmosphere creates approximately 85 times the atmospheric warming as a ton of CO2 over a period of 20 years.[20] On a 100-year timescale, methane's GWP100 is in the range of 28–34.

List of emission sources[edit]

The main sources of methane for the decade 2008–2017, estimated by the Global Carbon Project[14]
"Methane global emissions from the five broad categories for the 2008–2017 decade for top-down inversion models and for bottom-up models and inventories (right dark coloured box plots).[14][clarification needed]

Abiogenic methane is stored in rocks and soil stems from the geologic processes that convert ancient biomass into fossil fuels.[clarification needed][contradictory] Biogenic methane is actively produced by microorganisms in a process called methanogenesis. Under certain conditions, the process mix responsible for a sample of methane may be deduced from the ratio of the isotopes of carbon, and through analysis methods similar to carbon dating.[21][22]

Anthropogenic[edit]

Map of methane emissions from four source categories[14]

A comprehensive systems method from describing the sources of methane due to human society is known as anthropogenic metabolism.[clarification needed] As of 2020, emission volumes from some sources remain more uncertain than others; due in part to localized emission spikes not captured by the limited global measurement capability. The time required for a methane emission to become well-mixed throughout earth's troposphere is about 1–2 years.[23]

Satellite data indicate over 80% of the growth of methane emissions during 2010–2019 are tropical terrestrial emissions.[24][25]

Category Major Sources IEA Annual Emission[3]
(Million Tons)
Fossil fuels Gas distribution 45
Oil wells 39*
Coal mines 39
Biofuels Anaerobic digestion 11
Industrial agriculture Enteric fermentation 145
Rice paddies
Manure management
Biomass Biomass burning 16
Consumer waste Solid waste
Landfill gas
68
Wastewater
Total anthropogenic 363
* An additional 100 million tons (140 billion cubic meters) of gas is flared each year from oil wells.[26]
Additional References: [1][27][28][29][30]

Natural[edit]

Map of methane emissions from three natural sources and one sink.[14]

Natural sources have always been a part of the methane cycle. Wetland emissions have been declining due to draining for agricultural and building areas.

Category Major Sources IEA Annual Emission[3]
(Million Tons)
Wetlands Wetland methane 194
Other natural Geologic seepages
Volcanic gas
39
Arctic melting
Permafrost
Ocean sediments
Wildfires
Termites
Total natural 233
Additional References: [1][27][28]

Importance of methane emissions[edit]

Methane emissions are important as reducing them can buy time to tackle carbon emissions.[31][32]

Global monitoring[edit]

Uncertainties in methane emissions, including so-called "super-emitter" fossil extractions[33] and unexplained atmospheric fluctuations,[34] highlight the need for improved monitoring at both regional and global scale. Satellites have recently begun to come online with capability to measure methane and other more powerful greenhouse gases with improving resolution.[35][36][37]

The Tropomi[38] instrument on Sentinel-5 launched in 2017 by the European Space Agency can measure methane, sulphur dioxide, nitrogen dioxide, carbon monoxide, aerosol, and ozone concentrations in earth's troposphere at resolutions of several kilometers.[33][39][40] In 2022, a study using data from the instrument monitoring large methane emissions worldwide was published; 1,200 large methane plumes were detected over oil and gas extraction sites.[41]

Japan's GOSAT-2 platform launched in 2018 provides similar capability.[42]

The Claire satellite launched in 2016 by the Canadian firm GHGSat uses data from Tropomi to home in on sources of methane emissions as small as 15 m².[35]

Other satellites are planned that will increase the precision and frequency of methane measurements, as well as provide a greater ability to attribute emissions to terrestrial sources. These include MethaneSAT, expected to be launched in 2022, and CarbonMapper.

Global maps combining satellite data to help identify and monitor major methane emission sources are being built.[43][44][45]

National reduction policies[edit]

Global anthropogenic methane emissions from historical inventories and future Shared Socioeconomic Pathways (SSP) projections.[14]

China implemented regulations requiring coal plants to either capture methane emissions or convert methane into CO2 in 2010. According to a Nature Communications paper published in January 2019, methane emissions instead increased 50 percent between 2000 and 2015.[46][47]

In March 2020, Exxon called for stricter methane regulations, which would include detection and repair of leaks, minimization of venting and releases of unburned methane, and reporting requirements for companies.[48] However, in August 2020, the U.S. Environmental Protection Agency rescinded a prior tightening of methane emission rules for the U.S. oil and gas industry.[49][50]

Methane emissions for 2017 by region, source category, and latitude.[51]

Removal technology[edit]

Various approaches have been suggested to actively remove methane from the atmosphere. In 2019, researchers proposed a technique for removing methane from the atmosphere using zeolite. Each molecule of methane would be converted into CO
2
, which has a far smaller impact on climate (99% less). Replacing all atmospheric methane with CO
2
would reduce total greenhouse gas warming by approximately one-sixth.[52]

Zeolite is a crystalline material with a porous molecular structure.[52] Powerful fans could push air through reactors of zeolite and catalysts to absorb the methane. The reactor could then be heated to form and release CO
2
. Because of methane's higher GWP, at a carbon price of $500/ton removing one ton of methane would earn $12,000.[52]

In 2021, Methane Action proposed adding iron to seawater sprays from ship smokestacks. The group claimed that an amount equal to approximately 10% of the iron dust that already reaches the atmosphere could readily restore methane to pre-industrial levels.[53]

Another approach is to apply titanium dioxide paint to large surfaces.[53]

See also[edit]

References[edit]

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External links[edit]