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. During 2019, about 60% (360 million tons) of methane released globally was from human activities, while natural sources contributed about 40% (230 million tons). Reducing methane emissions by capturing and utilizing the gas can produce simultaneous environmental and economic benefits.
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. Animal agriculture is a similarly large source (30%); primarily because of enteric fermentation by ruminant livestock such as cattle and sheep. 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.
The world's wetlands contribute about three-quarters (75%) of the enduring natural sources of methane. Seepages from near-surface hydrocarbon and clathrate hydrate deposits, volcanic releases, wildfires, and termite emissions account for much of the remainder. Contributions from the surviving wild populations of ruminant mammals are vastly overwhelmed by those of cattle, humans, and other livestock animals.
Atmospheric concentration and warming influence
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. The methane itself causes direct radiative forcing that is second only to that of carbon dioxide (CO2). 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. 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.
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. 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. On a 100-year timescale, methane's GWP100 is in the range of 28–34.
List of emission sources
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.
A comprehensive systems method from describing the sources of methane due to human society is known as anthropogenic metabolism.[clarification needed] As of 2020[update], 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.
|Category||Major Sources||IEA Annual Emission|
|Fossil fuels||Gas distribution||45|
|Industrial agriculture||Enteric fermentation||145|
|Consumer waste||Solid waste
|* An additional 100 million tons (140 billion cubic meters) of gas is vented and flared each year from oil wells.|
Additional References: 
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|
|Other natural||Geologic seepages
|Additional References: |
Importance of fossil emissions
Unlike most other natural and human-caused emissions, fossil-fuel extraction and burning yields a net transfer of carbon between major storage pools in Earth's biosphere that will persist for millennia. In total, humans extracted about 400 billion tons (gigatonnes or petagrams) of geologic carbon through year 2015; including half in just the last one-third century and at an increasing rate of about 10 billion tons per year. The magnitude of this transfer exceeds that from any other known geologic event throughout all of human history. About 50 percent of the transferred carbon presently resides in the atmosphere in the form of elevated CO2 and CH4 concentrations. Much of the remainder has been taken up by the oceans as an increase in dissolved CO2 and carbonic acid especially near the water surface. The magnitude of the overall terrestrial vegetation sink has similarly grown despite the additional burden of land-use changes in some regions.
This carbon redistribution is the root cause of recent rapid global warming, ocean acidification, and their resulting impacts to life. Some of the largest effects, like sea level rise and desertification, occur over time due to the vast inertia of the Earth system. Assessing these and other environmental threats to the sustainability of human civilization are topics within Earth system science, including the recently proposed comprehensive framework of planetary boundaries. Despite the probable crossing of multiple boundaries by the early 21st century, there has been very limited international progress towards a corresponding framework or forum for planetary management.
Uncertainties in methane emissions, including so-called "super-emitter" fossil extractions and unexplained atmospheric fluctuations, 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. The Tropomi instrument launched in year 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. Japan's GOSAT-2 platform launched in 2018 provides similar capability. The CLAIRE satellite launched in year 2016 by the Canadian firm GHGSat can resolve carbon dioxide and methane to as little as 50 meters, thus enabling its customers to pinpoint the source of emissions.
National reduction policies
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.
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. 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.
|Antigua and Barbuda||24||43|
|Bosnia and Herzegovina||3,174||3,140|
|British Virgin Islands||13||19|
|Central African Republic||28,890||85,677|
|Congo, Dem. Rep.||119,583||75,336|
|Hong Kong SAR||704||3,147|
|Iran, Islamic Rep.||52,013||121,298|
|Isle of Man||n.a.||n.a.|
|Micronesia, Fed. Sts.||17||30|
|Northern Mariana Islands||2||12|
|Papua New Guinea||948||2,143|
|Sao Tome and Principe||17||46|
|Sint Maarten (Dutch part)||n.a.||n.a.|
|St. Kitts and Nevis||26||30|
|Saint Martin (French part)||n.a.||n.a.|
|St. Vincent and the Grenadines||23||40|
|Syrian Arab Republic||2,425||12,783|
|Trinidad and Tobago||1,596||14,789|
|Turks and Caicos Islands||1||6|
|United Arab Emirates||12,873||26,120|
|Virgin Islands (U.S.)||16||47|
|West Bank and Gaza||n.a.||n.a.|
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.
Zeolite is a crystalline material with a porous molecular structure. 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.
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