Methane#Methane as a greenhouse gas

File:Covalent.svg hydrogen and carbon in a molecule of methane.]]Methane is a tetrahedral molecule with four equivalent C–H bonds. Its electronic structure is described by four bonding molecular orbitals (MOs) resulting from the overlap of the valence orbitals on C and H. The lowest-energy MO is the result of the overlap of the 2s orbital on carbon with the in-phase combination of the 1s orbitals on the four hydrogen atoms. Above this energy level is a triply degenerate set of MOs that involve overlap of the 2p orbitals on carbon with various linear combinations of the 1s orbitals on hydrogen. The resulting "three-over-one" bonding scheme is consistent with photoelectron spectroscopic measurements.

Methane is an odorless, colourless and transparent gas at standard temperature and pressure.{{cite book |url=https://books.google.com/books?id=yp3qEgHrsJ4C&pg=PA168 |page=168 |title=Handbook of transport and the environment |author1=Hensher, David A. |author2=Button, Kenneth J. |publisher=Emerald Group Publishing |year=2003 |isbn=978-0-08-044103-0 |access-date=February 22, 2016 |archive-date=March 19, 2015 |archive-url=https://web.archive.org/web/20150319073323/http://books.google.com/books?id=yp3qEgHrsJ4C&pg=PA168 |url-status=live }} It does absorb visible light, especially at the red end of the spectrum, due to overtone bands, but the effect is only noticeable if the light path is very long. This is what gives Uranus and Neptune their blue or bluish-green colors, as light passes through their atmospheres containing methane and is then scattered back out.{{cite journal|display-authors=etal |last1=P.G.J Irwin |title=Hazy Blue Worlds: A Holistic Aerosol Model for Uranus and Neptune, Including Dark Spots |journal=Journal of Geophysical Research: Planets |date=Jan 12, 2022 |volume=127 |issue=6 |doi=10.1029/2022JE007189 |pmid=35865671 |arxiv=2201.04516 |s2cid=245877540 |pmc=9286428 |page=e2022JE007189|bibcode=2022JGRE..12707189I }}

The familiar smell of natural gas as used in homes is achieved by the addition of an odorant, usually blends containing tert-butylthiol, as a safety measure. Methane has a boiling point of −161.5 °C at a pressure of one atmosphere. As a gas, it is flammable over a range of concentrations (5.4%–17%) in air at standard pressure.

Solid methane exists in several modifications, of which nine are known.{{cite journal | last1 = Bini | first1 = R. | last2 = Pratesi | first2 = G. | year = 1997 | title = High-pressure infrared study of solid methane: Phase diagram up to 30 GPa | journal = Physical Review B | volume = 55 | issue = 22 | pages = 14800–14809 | doi=10.1103/physrevb.55.14800 | bibcode = 1997PhRvB..5514800B }} Cooling methane at normal pressure results in the formation of methane I. This substance crystallizes in the cubic system (space group Fm{{overline|3}}m). The positions of the hydrogen atoms are not fixed in methane I, i.e. methane molecules may rotate freely. Therefore, it is a plastic crystal.{{cite web |url=https://log-web.de/chemie/Start.htm?name=methaneCryst&lang=en |title=Crystal structures |access-date=December 10, 2019 |author=Wendelin Himmelheber |archive-date=February 12, 2020 |archive-url=https://web.archive.org/web/20200212105639/https://log-web.de/chemie/Start.htm?name=methaneCryst&lang=en |url-status=live }}

The primary chemical reactions of methane are combustion, steam reforming to syngas, and halogenation. In general, methane reactions are difficult to control.

Partial oxidation of methane to methanol (CH₃OH), a more convenient, liquid fuel, is challenging because the reaction typically progresses all the way to carbon dioxide and water even with an insufficient supply of oxygen. The enzyme methane monooxygenase produces methanol from methane, but cannot be used for industrial-scale reactions.{{cite journal |doi=10.1021/cr950244f |title=Mechanistic Studies on the Hydroxylation of Methane by Methane Monooxygenase |year=2003 |last1=Baik |first1=Mu-Hyun |last2=Newcomb |first2=Martin |last3=Friesner |first3=Richard A. |last4=Lippard |first4=Stephen J. |journal=Chemical Reviews |volume=103 |issue=6 |pages=2385–419 |pmid=12797835}} Some homogeneously catalyzed systems and heterogeneous systems have been developed, but all have significant drawbacks. These generally operate by generating protected products which are shielded from overoxidation. Examples include the Catalytica system, copper zeolites, and iron zeolites stabilizing the alpha-oxygen active site.{{Cite journal|last1=Snyder|first1=Benjamin E. R.|last2=Bols|first2=Max L.|last3=Schoonheydt|first3=Robert A.|last4=Sels|first4=Bert F.|last5=Solomon|first5=Edward I.|date=December 19, 2017|title=Iron and Copper Active Sites in Zeolites and Their Correlation to Metalloenzymes|journal=Chemical Reviews|volume=118|issue=5|pages=2718–2768|doi=10.1021/acs.chemrev.7b00344|pmid=29256242|url=https://lirias.kuleuven.be/handle/123456789/627682}}

One group of bacteria catalyze methane oxidation with nitrite as the oxidant in the absence of oxygen, giving rise to the so-called anaerobic oxidation of methane.

{{cite book

| first1=Joachim

| last1=Reimann

| first2=Mike S.M.

| last2=Jetten

| first3=Jan T.

| last3=Keltjens

| chapter=Metal Enzymes in "Impossible" Microorganisms Catalyzing the Anaerobic Oxidation of Ammonium and Methane

| editor=Peter M.H. Kroneck and Martha E. Sosa Torres

| title=Sustaining Life on Planet Earth: Metalloenzymes Mastering Dioxygen and Other Chewy Gases

| series=Metal Ions in Life Sciences

| volume=15

| year=2015

| publisher=Springer

| pages=257–313

| doi=10.1007/978-3-319-12415-5_7

| pmid=25707470

| isbn=978-3-319-12414-8

}}

Like other hydrocarbons, methane is an extremely weak acid. Its pK_a in DMSO is estimated to be 56.{{cite journal |doi=10.1021/ar00156a004 |title=Equilibrium acidities in dimethyl sulfoxide solution |year=1988 |last1=Bordwell |first1=Frederick G. |journal=Accounts of Chemical Research |volume=21 |issue=12 |pages=456–463|s2cid=26624076 }} It cannot be deprotonated in solution, but the conjugate base is known in forms such as methyllithium.

A variety of positive ions derived from methane have been observed, mostly as unstable species in low-pressure gas mixtures. These include methenium or methyl cation {{chem2|CH3+}}, methane cation {{chem2|CH4+}}, and methanium or protonated methane {{chem2|CH5+}}. Some of these have been detected in outer space. Methanium can also be produced as diluted solutions from methane with superacids. Cations with higher charge, such as {{chem2|CH6(2+)}} and {{chem2|CH7(3+)}}, have been studied theoretically and conjectured to be stable.

Despite the strength of its C–H bonds, there is intense interest in catalysts that facilitate C–H bond activation in methane (and other lower numbered alkanes).{{cite journal |doi=10.1126/science.1177485 |title=Characterization of a Rhodium(I) σ-Methane Complex in Solution |year=2009 |last1=Bernskoetter |first1=W. H. |last2= Schauer |first2=C. K. |last3=Goldberg |first3=K. I. |last4=Brookhart |first4=M. |journal=Science |volume=326 |issue=5952 |pages=553–556 |pmid=19900892 |bibcode=2009Sci...326..553B |s2cid=5597392 }}

File: The fire within her.jpg

Methane's heat of combustion is 55.5 MJ/kg.[http://people.hofstra.edu/geotrans/eng/ch8en/conc8en/energycontent.html Energy Content of some Combustibles (in MJ/kg)] {{Webarchive|url=https://web.archive.org/web/20140109145655/http://people.hofstra.edu/geotrans/eng/ch8en/conc8en/energycontent.html |date=January 9, 2014 }}. People.hofstra.edu. Retrieved on March 30, 2014. Combustion of methane is a multiple step reaction summarized as follows:

:{{chem2|CH4 + 2 O2 → CO2 + 2 H2O}}

:ΔH = −802 kJ/mol, at standard conditions (for water vapor, ΔH = −891 kJ/mol for liquid water)

Peters four-step chemistry is a systematically reduced four-step chemistry that explains the burning of methane.

Given appropriate conditions, methane reacts with halogen radicals as follows:

:{{chem2|•X + CH4 → HX + •CH3}}

:{{chem2|•CH3 + X2 → CH3X + •X}}

where X is a halogen: fluorine (F), chlorine (Cl), bromine (Br), or iodine (I). This mechanism for this process is called free radical halogenation. It is initiated when UV light or some other radical initiator (like peroxides) produces a halogen atom. A two-step chain reaction ensues in which the halogen atom abstracts a hydrogen atom from a methane molecule, resulting in the formation of a hydrogen halide molecule and a methyl radical ({{chem2|•CH3}}). The methyl radical then reacts with a molecule of the halogen to form a molecule of the halomethane, with a new halogen atom as byproduct.{{cite book |last1= March|first1=Jerry|title= Advance Organic Chemistry: Reactions, Mechanisms and Structure|year= 1968|publisher= McGraw-Hill Book Company|location= New York|pages= 533–534}} Similar reactions can occur on the halogenated product, leading to replacement of additional hydrogen atoms by halogen atoms with dihalomethane, trihalomethane, and ultimately, tetrahalomethane structures, depending upon reaction conditions and the halogen-to-methane ratio.

This reaction is commonly used with chlorine to produce dichloromethane and chloroform via chloromethane. Carbon tetrachloride can be made with excess chlorine.

Methane may be transported as a refrigerated liquid (liquefied natural gas, or LNG). While leaks from a refrigerated liquid container are initially heavier than air due to the increased density of the cold gas, the gas at ambient temperature is lighter than air. Gas pipelines distribute large amounts of natural gas, of which methane is the principal component.

Methane is used as a fuel for ovens, homes, water heaters, kilns, automobiles,{{Cite web|url=http://www.energymanagertoday.com/lumber-company-locates-kilns-at-landfill-to-use-methane-0115981/|title=Lumber Company Locates Kilns at Landfill to Use Methane – Energy Manager Today|website=Energy Manager Today|date=September 23, 2015|access-date=March 11, 2016|archive-date=July 9, 2019|archive-url=https://web.archive.org/web/20190709181604/https://www.energymanagertoday.com/lumber-company-locates-kilns-at-landfill-to-use-methane-0115981/|url-status=live}}{{cite news|quote=Compressed natural gas is touted as the 'cleanest burning' alternative fuel available, since the simplicity of the methane molecule reduces tailpipe emissions of different pollutants by 35 to 97%. Not quite as dramatic is the reduction in net greenhouse-gas emissions, which is about the same as corn-grain ethanol at about a 20% reduction over gasoline|url=http://www.gas2.org/2008/04/29/natural-gas-cars-cng-fuel-almost-free-in-some-parts-of-the-country/|title=Natural Gas Cars: CNG Fuel Almost Free in Some Parts of the Country|date=April 29, 2008|author=Cornell, Clayton B.|access-date=July 25, 2009|archive-url=https://web.archive.org/web/20190120033852/http://gas2.org/2008/04/29/natural-gas-cars-cng-fuel-almost-free-in-some-parts-of-the-country/|archive-date=January 20, 2019|url-status=dead}} turbines, etc.

As the major constituent of natural gas, methane is important for electricity generation by burning it as a fuel in a gas turbine or steam generator. Compared to other hydrocarbon fuels, methane produces less carbon dioxide for each unit of heat released. At about 891 kJ/mol, methane's heat of combustion is lower than that of any other hydrocarbon, but the ratio of the heat of combustion (891 kJ/mol) to the molecular mass (16.0 g/mol, of which 12.0 g/mol is carbon) shows that methane, being the simplest hydrocarbon, produces more heat per mass unit (55.7 kJ/g) than other complex hydrocarbons. In many areas with a dense enough population, methane is piped into homes and businesses for heating, cooking, and industrial uses. In this context it is usually known as natural gas, which is considered to have an energy content of 39 megajoules per cubic meter, or 1,000 BTU per standard cubic foot. Liquefied natural gas (LNG) is predominantly methane ({{chem2|CH4}}) converted into liquid form for ease of storage or transport.

{{See also|Liquid rocket propellant#Methane}}

Refined liquid methane as well as LNG is used as a rocket fuel,

{{cite journal |last=Thunnissen |first=Daniel P. |author2=Guernsey, C. S. |author3=Baker, R. S. |author4=Miyake, R. N. |year=2004 |title=Advanced Space Storable Propellants for Outer Planet Exploration |url=https://trs-new.jpl.nasa.gov/dspace/bitstream/2014/37950/1/04-0799.pdf |url-status=dead |journal=American Institute of Aeronautics and Astronautics |issue=4–0799 |pages=28 |archive-url=https://web.archive.org/web/20160310001026/https://trs-new.jpl.nasa.gov/dspace/bitstream/2014/37950/1/04-0799.pdf |archive-date=March 10, 2016}} when combined with liquid oxygen, as in the TQ-12, BE-4, Raptor, YF-215, and Aeon engines.{{Cite web |title=Blue Origin BE-4 Engine |url=https://www.blueorigin.com/engines/be-4 |url-status=live |archive-url=https://web.archive.org/web/20211001032523/https://www.blueorigin.com/engines/be-4 |archive-date=October 1, 2021 |access-date=June 14, 2019 |quote=We chose LNG because it is highly efficient, low cost and widely available. Unlike kerosene, LNG can be used to self-pressurize its tank. Known as autogenous repressurization, this eliminates the need for costly and complex systems that draw on Earth’s scarce helium reserves. LNG also possesses clean combustion characteristics even at low throttle, simplifying engine reuse compared to kerosene fuels.}} Due to the similarities between methane and LNG such engines are commonly grouped together under the term methalox.

As a liquid rocket propellant, a methane/liquid oxygen combination offers the advantage over kerosene/liquid oxygen combination, or kerolox, of producing small exhaust molecules, reducing coking or deposition of soot on engine components. Methane is easier to store than hydrogen due to its higher boiling point and density, as well as its lack of hydrogen embrittlement.{{cite news |title=SpaceX propulsion chief elevates crowd in Santa Barbara |url=http://www.pacbiztimes.com/2014/02/19/spacexs-propulsion-chief-elevates-crowd-in-santa-barbara/ |date=2014-02-19 |publisher=Pacific Business Times |access-date=2014-02-22}}{{cite web |last=Belluscio| first=Alejandro G. |title=SpaceX advances drive for Mars rocket via Raptor power |work=NASAspaceflight.com |date=2014-03-07 |url=http://www.nasaspaceflight.com/2014/03/spacex-advances-drive-mars-rocket-raptor-power/ |access-date=2014-03-07}} The lower molecular weight of the exhaust also increases the fraction of the heat energy which is in the form of kinetic energy available for propulsion, increasing the specific impulse of the rocket. Compared to liquid hydrogen, the specific energy of methane is lower but this disadvantage is offset by methane's greater density and temperature range, allowing for smaller and lighter tankage for a given fuel mass. Liquid methane has a temperature range (91–112 K) nearly compatible with liquid oxygen (54–90 K). The fuel currently sees use in operational launch vehicles such as Zhuque-2, Vulcan and New Glenn as well as in-development launchers such as Starship, Neutron, Terran R, Nova, and Long March 9.{{cite web|url=https://www.reuters.com/technology/space/china-beats-rivals-successfully-launch-first-methane-liquid-rocket-2023-07-12/ |title=China beats rivals to successfully launch first methane-liquid rocket |work=Reuters |date=12 July 2023 }}

Natural gas, which is mostly composed of methane, is used to produce hydrogen gas on an industrial scale. Steam methane reforming (SMR), or simply known as steam reforming, is the standard industrial method of producing commercial bulk hydrogen gas. More than 50 million metric tons are produced annually worldwide (2013), principally from the SMR of natural gas.[https://www.hydrogen.energy.gov/pdfs/hpep_report_2013.pdf Report of the Hydrogen Production Expert Panel: A Subcommittee of the Hydrogen & Fuel Cell Technical Advisory Committee] {{Webarchive|url=https://web.archive.org/web/20200214163130/https://www.hydrogen.energy.gov/pdfs/hpep_report_2013.pdf |date=February 14, 2020 }}. United States Department of Energy (May 2013). Much of this hydrogen is used in petroleum refineries, in the production of chemicals and in food processing. Very large quantities of hydrogen are used in the industrial synthesis of ammonia.

At high temperatures (700–1100 °C) and in the presence of a metal-based catalyst (nickel), steam reacts with methane to yield a mixture of CO and Dihydrogen, known as "water gas" or "syngas":

:{{chem2|CH4 + H2O ⇌ CO + 3 H2}}

This reaction is strongly endothermic (consumes heat, {{math|1=ΔH_r =}} 206 kJ/mol).

Additional hydrogen is obtained by the reaction of CO with water via the water-gas shift reaction:

:{{chem2|CO + H2O ⇌ CO2 + H2}}

This reaction is mildly exothermic (produces heat, {{math|1=ΔH_r =}} −41 kJ/mol).

Methane is also subjected to free-radical chlorination in the production of chloromethanes, although methanol is a more typical precursor.Rossberg, M. et al. (2006) "Chlorinated Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a06_233.pub2}}.

Hydrogen can also be produced via the direct decomposition of methane, also known as methane pyrolysis, which, unlike steam reforming, produces no greenhouse gases (GHG). The heat needed for the reaction can also be GHG emission free, e.g. from concentrated sunlight, renewable electricity, or burning some of the produced hydrogen. If the methane is from biogas then the process can be a carbon sink. Temperatures in excess of 1200 °C are required to break the bonds of methane to produce hydrogen gas and solid carbon.{{cite journal |last1=Lumbers |first1=Brock |title=Mathematical modelling and simulation of the thermo-catalytic decomposition of methane for economically improved hydrogen production |url=https://www.sciencedirect.com/science/article/abs/pii/S0360319921044438 |journal=International Journal of Hydrogen Energy |year=2022 |volume=47 |issue=7 |pages=4265–4283 |doi=10.1016/j.ijhydene.2021.11.057 |bibcode=2022IJHE...47.4265L |s2cid=244814932 |access-date=15 June 2022}}

However, through the use of a suitable catalyst the reaction temperature can be reduced to between 550 and 900 °C depending on the chosen catalyst. Dozens of catalysts have been tested, including unsupported and supported metal catalysts, carbonaceous and metal-carbon catalysts.{{Cite journal |last1=Hamdani |first1=Iqra R. |last2=Ahmad |first2=Adeel |last3=Chulliyil |first3=Haleema M. |last4=Srinivasakannan |first4=Chandrasekar |last5=Shoaibi |first5=Ahmed A. |last6=Hossain |first6=Mohammad M. |date=2023-08-15 |title=Thermocatalytic Decomposition of Methane: A Review on Carbon-Based Catalysts |journal=ACS Omega |language=en |volume=8 |issue=32 |pages=28945–28967 |doi=10.1021/acsomega.3c01936 |issn=2470-1343 |pmc=10433352 |pmid=37599913}}

The reaction is moderately endothermic as shown in the reaction equation below.{{cite journal |last1=Lumbers |first1=Brock |year=2022 |title=Low-emission hydrogen production via the thermo-catalytic decomposition of methane for the decarbonisation of iron ore mines in Western Australia |url=https://www.sciencedirect.com/science/article/abs/pii/S0360319922011855 |journal=International Journal of Hydrogen Energy |volume=47 |issue=37 |pages=16347–16361 |bibcode=2022IJHE...4716347L |doi=10.1016/j.ijhydene.2022.03.124 |s2cid=248018294 |access-date=10 July 2022}}

:{{chem2|CH4(g) → C(s) + 2 H2(g)}}

:({{math|1=ΔH° =}} 74.8 kJ/mol)

As a refrigerant, methane has the ASHRAE designation R-50.

File:Global Methane Budget 2017.jpg

Methane can be generated through geological, biological or industrial routes.

{{See also|Biogeochemistry}}

File:Origins_of_Biotic_and_Abiotic_Methane.jpgThe two main routes for geological methane generation are (i) organic (thermally generated, or thermogenic) and (ii) inorganic (abiotic). Thermogenic methane occurs due to the breakup of organic matter at elevated temperatures and pressures in deep sedimentary strata. Most methane in sedimentary basins is thermogenic; therefore, thermogenic methane is the most important source of natural gas. Thermogenic methane components are typically considered to be relic (from an earlier time). Generally, formation of thermogenic methane (at depth) can occur through organic matter breakup, or organic synthesis. Both ways can involve microorganisms (methanogenesis), but may also occur inorganically. The processes involved can also consume methane, with and without microorganisms.

The more important source of methane at depth (crystalline bedrock) is abiotic. Abiotic means that methane is created from inorganic compounds, without biological activity, either through magmatic processes{{examples needed|date=June 2024}} or via water-rock reactions that occur at low temperatures and pressures, like serpentinization.{{cite journal|author=Kietäväinen and Purkamo|year=2015|title=The origin, source, and cycling of methane in deep crystalline rock biosphere|journal=Front. Microbiol.|volume=6|page=725|doi=10.3389/fmicb.2015.00725|pmc=4505394|pmid=26236303|doi-access=free}}{{cite journal|author=Cramer and Franke|year=2005|title=Indications for an active petroleum system in the Laptev Sea, NE Siberia|url=https://www.researchgate.net/publication/227744258|journal=Journal of Petroleum Geology|volume=28|issue=4|pages=369–384|bibcode=2005JPetG..28..369C|doi=10.1111/j.1747-5457.2005.tb00088.x|s2cid=129445357 |doi-access=|access-date=May 23, 2017|archive-date=October 1, 2021|archive-url=https://web.archive.org/web/20211001032525/https://www.researchgate.net/publication/227744258_Indications_for_an_active_petroleum_system_in_the_Laptev_Sea_NE_Siberia|url-status=live}}

{{Main|Methanogenesis}}

Most of Earth's methane is biogenic and is produced by methanogenesis,Lessner, Daniel J. (Dec 2009) Methanogenesis Biochemistry. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net {{Webarchive|url=https://web.archive.org/web/20110513234028/http://www.els.net/ |date=May 13, 2011|doi=10.1002/9780470015902.a0000573.pub2}}{{Citation |last=Thiel |first=Volker |chapter=Methane Carbon Cycling in the Past: Insights from Hydrocarbon and Lipid Biomarkers |date=2018 |pages=1–30 |editor-last=Wilkes |editor-first=Heinz |series=Handbook of Hydrocarbon and Lipid Microbiology |publisher=Springer International Publishing |doi=10.1007/978-3-319-54529-5_6-1 |isbn=9783319545295 |title=Hydrocarbons, Oils and Lipids: Diversity, Origin, Chemistry and Fate|s2cid=105761461 }} a form of anaerobic respiration only known to be conducted by some members of the domain Archaea.{{Cite journal |last1=Dean |first1=Joshua F. |last2=Middelburg |first2=Jack J. |last3=Röckmann |first3=Thomas |last4=Aerts |first4=Rien |last5=Blauw |first5=Luke G. |last6=Egger |first6=Matthias |last7=Jetten |first7=Mike S. M. |last8=de Jong |first8=Anniek E. E. |last9=Meisel |first9=Ove H. |date=2018 |title=Methane Feedbacks to the Global Climate System in a Warmer World |journal=Reviews of Geophysics |volume=56 |issue=1 |pages=207–250 |doi=10.1002/2017RG000559 |bibcode=2018RvGeo..56..207D|hdl=1874/366386 |doi-access=free |hdl-access=free }} Methanogens occur in landfills and soils,{{Cite journal |last1=Serrano-Silva |first1=N. |last2=Sarria-Guzman |first2=Y. |last3=Dendooven |first3=L. |last4=Luna-Guido |first4=M. |date=2014 |title=Methanogenesis and methanotrophy in soil: a review |journal=Pedosphere |volume=24 |issue=3 |pages=291–307 |doi=10.1016/s1002-0160(14)60016-3|bibcode=2014Pedos..24..291S }} ruminants (for example, cattle),{{Cite journal |last1=Sirohi |first1=S. K. |last2=Pandey |first2=Neha |last3=Singh |first3=B. |last4=Puniya |first4=A. K. |date=September 1, 2010 |title=Rumen methanogens: a review |journal=Indian Journal of Microbiology |volume=50 |issue=3 |pages=253–262 |doi=10.1007/s12088-010-0061-6 |pmc=3450062 |pmid=23100838}} the guts of termites, and the anoxic sediments below the seafloor and the bottom of lakes.

This multistep process is used by these microorganisms for energy. The net reaction of methanogenesis is:

:{{chem2|CO2 + 4 H2 → CH4 + 2 H2O}}

The final step in the process is catalyzed by the enzyme methyl coenzyme M reductase (MCR).{{Cite journal |last1=Lyu |first1=Zhe |last2=Shao |first2=Nana |last3=Akinyemi |first3=Taiwo |last4=Whitman |first4=William B. |date=2018 |title=Methanogenesis |journal=Current Biology |volume=28 |issue=13 |pages=R727–R732 |doi=10.1016/j.cub.2018.05.021 |pmid=29990451|doi-access=free |bibcode=2018CBio...28.R727L }}File:CSIRO ScienceImage 1898 Testing Sheep for Methane Production.jpg]]

File:The Creation of Methane Within a Ruminant.svg

{{See also|Greenhouse gas emissions from wetlands}}

Wetlands are the largest natural sources of methane to the atmosphere,{{Cite web |last=Tandon |first=Ayesha |date=2023-03-20 |title='Exceptional' surge in methane emissions from wetlands worries scientists |url=https://www.carbonbrief.org/exceptional-surge-in-methane-emissions-from-wetlands-worries-scientists/ |access-date=2023-09-18 |website=Carbon Brief |language=en}} accounting for approximately 20 – 30% of atmospheric methane. Climate change is increasing the amount of methane released from wetlands due to increased temperatures and altered rainfall patterns. This phenomenon is called wetland methane feedback.

Rice cultivation generates as much as 12% of total global methane emissions due to the long-term flooding of rice fields.{{Cite web |last=Global Environment Facility |date=2019-12-07 |title=We can grow more climate-friendly rice |url=https://www.climatechangenews.com/2019/12/07/can-grow-climate-friendly-rice/ |access-date=2023-09-18 |website=Climate Home News |language=en}}

Ruminants such as cattle belch out methane, accounting for about 22% of the U.S. annual methane emissions to the atmosphere.{{cite web |date=2016 |title=Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014 |url=https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks-1990-2014 |journal= |access-date=April 11, 2019 |archive-date=April 12, 2019 |archive-url=https://web.archive.org/web/20190412070024/https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks-1990-2014 |url-status=live }}{{page needed|date=August 2021}} One study reported that the livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane.{{cite book |url=http://www.fao.org/docrep/010/a0701e/a0701e00.HTM |title=Livestock's Long Shadow–Environmental Issues and Options |author=FAO |publisher=Food and Agriculture Organization of the United Nations (FAO) |year=2006 |location=Rome, Italy |access-date=October 27, 2009 |archive-date=July 26, 2008 |archive-url=https://web.archive.org/web/20080726214204/http://www.fao.org/docrep/010/a0701e/a0701e00.htm |url-status=live }} A 2013 study estimated that livestock accounted for 44% of human-induced methane and about 15% of human-induced greenhouse gas emissions.{{cite web |url=http://www.fao.org/3/a-i3437e/index.html |title=Tackling Climate Change Through Livestock |author1=Gerber, P.J. |author2=Steinfeld, H. |date=2013 |publisher=Food and Agriculture Organization of the United Nations (FAO) |location=Rome |author3=Henderson, B. |author4=Mottet, A. |author5=Opio, C. |author6=Dijkman, J. |author7=Falcucci, A. |author8=Tempio, G. |name-list-style=amp |access-date=July 15, 2016 |archive-date=July 19, 2016 |archive-url=https://web.archive.org/web/20160719043314/http://www.fao.org/3/a-i3437e/index.html |url-status=dead }} Many efforts are underway to reduce livestock methane production, such as medical treatments and dietary adjustments,{{cite magazine |url=http://news.nationalgeographic.com/news/2002/05/0509_020509_belch.html |title=New Zealand Tries to Cap Gaseous Sheep Burps |author=Roach, John |date=May 13, 2002 |magazine=National Geographic |access-date=March 2, 2011 |archive-date=June 4, 2011 |archive-url=https://web.archive.org/web/20110604031223/http://news.nationalgeographic.com/news/2002/05/0509_020509_belch.html |url-status=dead }}{{Cite journal|last1=Roque|first1=Breanna M. |last2=Venegas |first2=Marielena|last3=Kinley|first3=Robert D.|last4=Nys|first4=Rocky de|last5=Duarte|first5=Toni L.|last6=Yang |first6=Xiang|last7=Kebreab |first7=Ermias |date=March 17, 2021|title=Red seaweed (Asparagopsis taxiformis) supplementation reduces enteric methane by over 80 percent in beef steers|journal=PLOS ONE|language=en|volume=16|issue=3|pages=e0247820|doi=10.1371/journal.pone.0247820|pmid=33730064|pmc=7968649|bibcode=2021PLoSO..1647820R|issn=1932-6203|doi-access=free}} and to trap the gas to use its combustion energy.{{cite web |url=http://science.howstuffworks.com/environmental/life/zoology/mammals/methane-cow.htm |title=Do cows pollute as much as cars? |author=Silverman, Jacob |date=July 16, 2007 |publisher=HowStuffWorks.com |access-date=November 7, 2012 |archive-date=November 4, 2012 |archive-url=https://web.archive.org/web/20121104141956/http://science.howstuffworks.com/environmental/life/zoology/mammals/methane-cow.htm |url-status=live }}

Most of the subseafloor is anoxic because oxygen is removed by aerobic microorganisms within the first few centimeters of the sediment. Below the oxygen-replete seafloor, methanogens produce methane that is either used by other organisms or becomes trapped in gas hydrates. These other organisms that utilize methane for energy are known as methanotrophs ('methane-eating'), and are the main reason why little methane generated at depth reaches the sea surface. Consortia of Archaea and Bacteria have been found to oxidize methane via anaerobic oxidation of methane (AOM); the organisms responsible for this are anaerobic methanotrophic Archaea (ANME) and sulfate-reducing bacteria (SRB).{{Citation |last1=Knittel |first1=K. |title=Anaerobic Methane Oxidizers |date=2019 |work=Microbial Communities Utilizing Hydrocarbons and Lipids: Members, Metagenomics and Ecophysiology |pages=1–21 |editor-last=McGenity |editor-first=Terry J. |series=Handbook of Hydrocarbon and Lipid Microbiology |publisher=Springer International Publishing |doi=10.1007/978-3-319-60063-5_7-1 |isbn=9783319600635 |last2=Wegener |first2=G. |last3=Boetius |first3=A.}}

File:Diagram of sustainable methane fuel production-en.svg, Sabatier reaction|upright=1.35]]

Given its cheap abundance in natural gas, there is little incentive to produce methane industrially. Methane can be produced by hydrogenating carbon dioxide through the Sabatier process. Methane is also a side product of the hydrogenation of carbon monoxide in the Fischer–Tropsch process, which is practiced on a large scale to produce longer-chain molecules than methane.

An example of large-scale coal-to-methane gasification is the Great Plains Synfuels plant, started in 1984 in Beulah, North Dakota as a way to develop abundant local resources of low-grade lignite, a resource that is otherwise difficult to transport for its weight, ash content, low calorific value and propensity to spontaneous combustion during storage and transport. A number of similar plants exist around the world, although mostly these plants are targeted towards the production of long chain alkanes for use as gasoline, diesel, or feedstock to other processes.

Power to methane is a technology that uses electrical power to produce hydrogen from water by electrolysis and uses the Sabatier reaction to combine hydrogen with carbon dioxide to produce methane.

Methane can be produced by protonation of methyl lithium or a methyl Grignard reagent such as methylmagnesium chloride. It can also be made from anhydrous sodium acetate and dry sodium hydroxide, mixed and heated above 300 °C (with sodium carbonate as byproduct).{{citation needed|date=January 2021}} In practice, a requirement for pure methane can easily be fulfilled by steel gas bottle from standard gas suppliers.

Methane is the major component of natural gas, about 87% by volume. The major source of methane is extraction from geological deposits known as natural gas fields, with coal seam gas extraction becoming a major source (see coal bed methane extraction, a method for extracting methane from a coal deposit, while enhanced coal bed methane recovery is a method of recovering methane from non-mineable coal seams). It is associated with other hydrocarbon fuels, and sometimes accompanied by helium and nitrogen. Methane is produced at shallow levels (low pressure) by anaerobic decay of organic matter and reworked methane from deep under the Earth's surface. In general, the sediments that generate natural gas are buried deeper and at higher temperatures than those that contain oil.

Methane is generally transported in bulk by pipeline in its natural gas form, or by LNG carriers in its liquefied form; few countries transport it by truck.

{{anchor|Methane in Earth.27s atmosphere}}

{{anchor|Methane as a greenhouse gas}}

{{Main|Atmospheric methane}}

File:CH4 mm.png) at stations around the world. Abundances are given as pollution free monthly mean mole fractions in parts-per-billion.]]

Methane is an important greenhouse gas, responsible for around 30% of the rise in global temperatures since the industrial revolution.{{Cite web |date=2022 |title=Methane and climate change – Global Methane Tracker 2022 – Analysis |url=https://www.iea.org/reports/global-methane-tracker-2022/methane-and-climate-change |access-date=2023-09-18 |website=IEA |language=en-GB}}

Methane has a global warming potential (GWP) of 29.8 ± 11 compared to {{chem2|CO2}} (potential of 1) over a 100-year period, and 82.5 ± 25.8 over a 20-year period.{{Cite book| publisher = Cambridge University Press| pages = 923–1054| last1 = Forster| first1 = P.| last2 = Storelvmo| first2 = T.| last3 = Armour| first3 = K.| last4 = Collins| first4 = W.| last5 = Dufresne| first5 = J.-L.| last6 = Frame| first6 = D.| last7 = Lunt| first7 = D.J.| last8 = Mauritsen| first8 = T.| last9 = Palmer| first9 = M.D.| last10 = Watanabe| first10 = M.| last11 = Wild| first11 = M.| last12 = Zhang| first12 = H.| title = Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change| chapter = The Earth’s Energy Budget, Climate Feedbacks, and Climate Sensitivity| location = Cambridge, United Kingdom and New York, NY, US| date = 2021| chapter-url = https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-7/}} This means that, for example, a leak of one tonne of methane is equivalent to emitting 82.5 tonnes of carbon dioxide. Burning methane and producing carbon dioxide also reduces the greenhouse gas impact compared to simply venting methane to the atmosphere.

File:Sources of methane emissions, 2021.jpg

As methane is gradually converted into carbon dioxide (and water) in the atmosphere, these values include the climate forcing from the carbon dioxide produced from methane over these timescales.

Annual global methane emissions are currently approximately 580 Mt,{{Cite web |title=Global Methane Budget 2020 |url=https://www.globalcarbonproject.org/methanebudget/ |access-date=2023-09-18 |website=www.globalcarbonproject.org |language=en}} 40% of which is from natural sources and the remaining 60% originating from human activity, known as anthropogenic emissions. The largest anthropogenic source is agriculture, responsible for around one quarter of emissions, closely followed by the energy sector, which includes emissions from coal, oil, natural gas and biofuels.{{Cite web |title=Methane and climate change – Global Methane Tracker 2022 – Analysis |url=https://www.iea.org/reports/global-methane-tracker-2022/methane-and-climate-change |access-date=2023-09-18 |website=IEA |language=en-GB}}

Historic methane concentrations in the world's atmosphere have ranged between 300 and 400 nmol/mol during glacial periods commonly known as ice ages, and between 600 and 700 nmol/mol during the warm interglacial periods. A 2012 NASA website said the oceans were a potential important source of Arctic methane,{{cite web |date=April 22, 2012 |title=Study Finds Surprising Arctic Methane Emission Source |url=http://www.nasa.gov/topics/earth/features/earth20120422.html |url-status=live |archive-url=https://web.archive.org/web/20140804084035/http://www.nasa.gov/topics/earth/features/earth20120422.html |archive-date=August 4, 2014 |access-date=March 30, 2014 |website=NASA}} but more recent studies associate increasing methane levels as caused by human activity.

Global monitoring of atmospheric methane concentrations began in the 1980s. The Earth's atmospheric methane concentration has increased 160% since preindustrial levels in the mid-18th century. In 2013, atmospheric methane accounted for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases.IPCC. {{Citation |title=Anthropogenic and Natural Radiative Forcing |date=2013 |url=http://dx.doi.org/10.1017/cbo9781107415324.018 |work=Climate Change 2013 – The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. |pages=659–740 |access-date=2023-09-18 |publisher=Cambridge University Press|doi=10.1017/cbo9781107415324.018 |isbn=9781107057999 }} Between 2011 and 2019 the annual average increase of methane in the atmosphere was 1866 ppb. From 2015 to 2019 sharp rises in levels of atmospheric methane were recorded.{{cite journal |last1=Nisbet |first1=E.G. |title=Very Strong Atmospheric Methane Growth in the 4 Years 2014–2017: Implications for the Paris Agreement |journal=Global Biogeochemical Cycles |date=February 5, 2019 |volume=33 |issue=3 |pages=318–342 |doi=10.1029/2018GB006009 |bibcode=2019GBioC..33..318N |doi-access=free }}{{Cite news |url=https://www.theguardian.com/environment/2019/feb/17/methane-levels-sharp-rise-threaten-paris-climate-agreement |title=Sharp rise in methane levels threatens world climate targets |last=McKie |first=Robin |date=February 2, 2017 |work=The Observer |access-date=July 14, 2019 |issn=0029-7712 |archive-date=July 30, 2019 |archive-url=https://web.archive.org/web/20190730181041/https://www.theguardian.com/environment/2019/feb/17/methane-levels-sharp-rise-threaten-paris-climate-agreement |url-status=live }}

In 2019, the atmospheric methane concentration was higher than at any time in the last 800,000 years. As stated in the AR6 of the IPCC, "Since 1750, increases in {{chem2|CO2}} (47%) and {{chem2|CH4}} (156%) concentrations far exceed, and increases in {{chem2|N2O}} (23%) are similar to, the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years (very high confidence)".{{efn|In 2013 Intergovernmental Panel on Climate Change (IPCC) scientists warned atmospheric concentrations of methane had "exceeded the pre-industrial levels by about 150% which represented "levels unprecedented in at least the last 800,000 years."}}{{cite report |url=https://www.ipcc.ch/site/assets/uploads/2018/03/WG1AR5_SummaryVolume_FINAL.pdf |title=Climate Change 2013: The Physical Science Basis |author=IPCC |author-link=IPCC |year=2013 |series=Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change |display-editors=4 |editor1-first=T. F. |editor1-last=Stocker |editor2-first=D. |editor2-last=Qin |editor3-first=G.-K. |editor3-last=Plattner |editor4-first=M. |editor4-last=Tignor |editor5-first=S. K. |editor5-last=Allen |editor6-first=J. |editor6-last=Boschung |editor7-first=A. |editor7-last=Nauels |editor8-first=Y. |editor8-last=Xia |editor9-first=V. |editor9-last=Bex |editor10-first=P. M. |editor10-last=Midgley}}

In February 2020, it was reported that fugitive emissions and gas venting from the fossil fuel industry may have been significantly underestimated.{{Cite journal| doi = 10.1038/s41586-020-1991-8| issn = 1476-4687| volume = 578| issue = 7795| pages = 409–412| last1 = Hmiel| first1 = Benjamin| last2 = Petrenko| first2 = V. V.| last3 = Dyonisius| first3 = M. N.| last4 = Buizert| first4 = C.| last5 = Smith| first5 = A. M.| last6 = Place| first6 = P. F.| last7 = Harth| first7 = C.| last8 = Beaudette| first8 = R.| last9 = Hua| first9 = Q.| last10 = Yang| first10 = B.| last11 = Vimont| first11 = I.| last12 = Michel| first12 = S. E.| last13 = Severinghaus| first13 = J. P.| last14 = Etheridge| first14 = D.| last15 = Bromley| first15 = T.| last16 = Schmitt| first16 = J.| last17 = Faïn| first17 = X.| last18 = Weiss| first18 = R. F.| last19 = Dlugokencky| first19 = E.| title = Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions| journal = Nature| access-date = March 15, 2023 | date = February 2020 | pmid = 32076219| bibcode = 2020Natur.578..409H| s2cid = 211194542| url = https://www.nature.com/articles/s41586-020-1991-8}}

{{cite magazine |first=Chelsea |last=Harvey |url=https://www.scientificamerican.com/article/methane-emissions-from-oil-and-gas-may-be-significantly-underestimated |title=Methane Emissions from Oil and Gas May Be Significantly Underestimated; Estimates of methane coming from natural sources have been too high, shifting the burden to human activities |archive-url=https://web.archive.org/web/20200224100051/https://www.scientificamerican.com/article/methane-emissions-from-oil-and-gas-may-be-significantly-underestimated/ |archive-date=February 24, 2020 |date=February 21, 2020 |magazine=E&E News via Scientific American}} The largest annual increase occurred in 2021 with the overwhelming percentage caused by human activity.

Climate change can increase atmospheric methane levels by increasing methane production in natural ecosystems, forming a climate change feedback.Carrington, Damian (July 21, 2020) [https://www.theguardian.com/environment/2020/jul/22/first-active-leak-of-sea-bed-methane-discovered-in-antarctica First active leak of sea-bed methane discovered in Antarctica] {{Webarchive|url=https://web.archive.org/web/20200722180152/https://www.theguardian.com/environment/2020/jul/22/first-active-leak-of-sea-bed-methane-discovered-in-antarctica |date=July 22, 2020 }}, The Guardian Another explanation for the rise in methane emissions could be a slowdown of the chemical reaction that removes methane from the atmosphere.{{Cite web |last=Ravilious |first=Kate |date=2022-07-05 |title=Methane much more sensitive to global heating than previously thought – study |url=https://www.theguardian.com/environment/2022/jul/05/global-heating-causes-methane-growth-four-times-faster-than-thought-study |access-date=2022-07-05 |website=The Guardian |language=en}}

Over 100 countries have signed the [https://www.globalmethanepledge.org/ Global Methane Pledge], launched in 2021, promising to cut their methane emissions by 30% by 2030.{{Cite web |last=Global Methane Pledge |title=Homepage {{!}} Global Methane Pledge |url=https://www.globalmethanepledge.org/ |access-date=2023-08-02 |website=www.globalmethanepledge.org}} This could avoid 0.2 °C of warming globally by 2050, although there have been calls for higher commitments in order to reach this target.{{Cite web |last1=Forster |first1=Piers |last2=Smith |first2=Chris |last3=Rogelj |first3=Joeri |date=2021-11-02 |title=Guest post: The Global Methane Pledge needs to go further to help limit warming to 1.5C |url=https://www.carbonbrief.org/guest-post-the-global-methane-pledge-needs-to-go-further-to-help-limit-warming-to-1-5c/ |access-date=2023-08-02 |website=Carbon Brief |language=en}} The International Energy Agency's 2022 report states "the most cost-effective opportunities for methane abatement are in the energy sector, especially in oil and gas operations".{{Cite web |last=IEA |date=2022 |title=Global Methane Tracker 2022 |url=https://www.iea.org/reports/global-methane-tracker-2022 |access-date=2023-08-02 |website=IEA |language=en-GB}}

Methane clathrates (also known as methane hydrates) are solid cages of water molecules that trap single molecules of methane. Significant reservoirs of methane clathrates have been found in arctic permafrost and along continental margins beneath the ocean floor within the gas clathrate stability zone, located at high pressures (1 to 100 MPa; lower end requires lower temperature) and low temperatures (< 15 °C; upper end requires higher pressure).{{Citation|last1=Bohrmann|first1=Gerhard|title=Gas Hydrates in Marine Sediments|date=2006|work=Marine Geochemistry|pages=481–512|editor-last=Schulz|editor-first=Horst D.|publisher=Springer Berlin Heidelberg|doi=10.1007/3-540-32144-6_14|isbn=9783540321446|last2=Torres|first2=Marta E.|editor2-last=Zabel|editor2-first=Matthias|doi-access=}} Methane clathrates can form from biogenic methane, thermogenic methane, or a mix of the two. These deposits are both a potential source of methane fuel as well as a potential contributor to global warming.Miller, G. Tyler (2007). Sustaining the Earth: An Integrated Approach. U.S.: Thomson Advantage Books, p. 160. {{ISBN|0534496725}}{{Cite journal|last=Dean|first=J. F.|date=2018|title=Methane feedbacks to the global climate system in a warmer world|journal=Reviews of Geophysics |volume=56 |issue=1 |pages=207–250 |doi=10.1002/2017RG000559 |bibcode=2018RvGeo..56..207D |hdl=1874/366386 |doi-access=free|hdl-access=free }} The global mass of carbon stored in gas clathrates is still uncertain and has been estimated as high as 12,500 Gt carbon and as low as 500 Gt carbon.{{Cite journal |last1=Boswell |first1=Ray |last2=Collett |first2=Timothy S.|date=2011|title=Current perspectives on gas hydrate resources|journal=Energy Environ. Sci.|volume=4|issue=4|pages=1206–1215|doi=10.1039/c0ee00203h}} The estimate has declined over time with a most recent estimate of ≈1800 Gt carbon.{{cite journal|last1=Ruppel |last2=Kessler|year=2017|title=The interaction of climate change and methane hydrates|journal=Reviews of Geophysics|volume=55|issue=1|pages=126–168|bibcode=2017RvGeo..55..126R|doi=10.1002/2016RG000534|url=https://zenodo.org/record/1000665|doi-access=free|access-date=September 16, 2019|archive-date=February 7, 2020|archive-url=https://web.archive.org/web/20200207003919/https://zenodo.org/record/1000665|url-status=live|hdl=1912/8978|hdl-access=free}} A large part of this uncertainty is due to our knowledge gap in sources and sinks of methane and the distribution of methane clathrates at the global scale. For example, a source of methane was discovered relatively recently in an ultraslow spreading ridge in the Arctic.{{Cite web|url=https://phys.org/news/2015-04-source-methane-arctic-ocean.html|title=New source of methane discovered in the Arctic Ocean|date=May 1, 2015|website=phys.org|access-date=April 10, 2019|archive-date=April 10, 2019|archive-url=https://web.archive.org/web/20190410210303/https://phys.org/news/2015-04-source-methane-arctic-ocean.html|url-status=live}} Some climate models suggest that today's methane emission regime from the ocean floor is potentially similar to that during the period of the Paleocene–Eocene Thermal Maximum (PETM) around 55.5 million years ago, although there are no data indicating that methane from clathrate dissociation currently reaches the atmosphere. Arctic methane release from permafrost and seafloor methane clathrates is a potential consequence and further cause of global warming; this is known as the clathrate gun hypothesis.{{cite press release |url=https://www.nsf.gov/news/news_summ.jsp?cntn_id=116532&org=NSF&from=news |title=Methane Releases From Arctic Shelf May Be Much Larger and Faster Than Anticipated|publisher=National Science Foundation (NSF)|date=March 10, 2010|access-date=April 6, 2018|archive-date=August 1, 2018 |archive-url=https://web.archive.org/web/20180801212512/https://www.nsf.gov/news/news_summ.jsp?cntn_id=116532&org=NSF&from=news |url-status=live}}{{cite news|url=https://www.independent.co.uk/news/science/methane-discovery-stokes-new-global-warming-fears-shock-as-retreat-of-arctic-releases-greenhouse-gas-6276278.html|title=Vast methane 'plumes' seen in Arctic ocean as sea ice retreats|author=Connor, Steve|date=December 13, 2011|newspaper=The Independent|access-date=September 4, 2017|archive-date=December 25, 2011|archive-url=https://web.archive.org/web/20111225132405/http://www.independent.co.uk/news/science/methane-discovery-stokes-new-global-warming-fears-shock-as-retreat-of-arctic-releases-greenhouse-gas-6276278.html|url-status=live}}{{cite press release|url=http://nsidc.org/news/press/2012_seaiceminimum.html|title=Arctic sea ice reaches lowest extent for the year and the satellite record|publisher=The National Snow and Ice Data Center (NSIDC)|date=September 19, 2012|access-date=October 7, 2012|archive-date=October 4, 2012|archive-url=https://web.archive.org/web/20121004124913/http://nsidc.org/news/press/2012_seaiceminimum.html|url-status=live}}{{Cite web|url=http://www.unenvironment.org/resources/frontiers-201819-emerging-issues-environmental-concern|title=Frontiers 2018/19: Emerging Issues of Environmental Concern|website=UN Environment|access-date=March 6, 2019|archive-date=March 6, 2019|archive-url=https://web.archive.org/web/20190306150402/https://www.unenvironment.org/resources/frontiers-201819-emerging-issues-environmental-concern|url-status=dead}} Data from 2016 indicate that Arctic permafrost thaws faster than predicted.{{Cite news|url=https://www.theguardian.com/environment/2019/jun/18/arctic-permafrost-canada-science-climate-crisis|title=Scientists shocked by Arctic permafrost thawing 70 years sooner than predicted|agency=Reuters|date=June 18, 2019|newspaper=The Guardian|access-date=July 14, 2019|issn=0261-3077|archive-date=October 6, 2019|archive-url=https://web.archive.org/web/20191006020220/https://www.theguardian.com/environment/2019/jun/18/arctic-permafrost-canada-science-climate-crisis|url-status=live}}

File:Abatement potential of policy measures, 2021.jpg

Methane "degrades air quality and adversely impacts human health, agricultural yields, and ecosystem productivity".{{Cite journal |last1=Shindell |first1=Drew |last2=Kuylenstierna |first2=Johan C. I. |last3=Vignati |first3=Elisabetta |last4=van Dingenen |first4=Rita |last5=Amann |first5=Markus |last6=Klimont |first6=Zbigniew |last7=Anenberg |first7=Susan C. |last8=Muller |first8=Nicholas |last9=Janssens-Maenhout |first9=Greet |last10=Raes |first10=Frank |last11=Schwartz |first11=Joel |last12=Faluvegi |first12=Greg |last13=Pozzoli |first13=Luca |last14=Kupiainen |first14=Kaarle |last15=Höglund-Isaksson |first15=Lena |date=2012-01-13 |title=Simultaneously mitigating near-term climate change and improving human health and food security |journal=Science |volume=335 |issue=6065 |pages=183–189 |bibcode=2012Sci...335..183S |doi=10.1126/science.1210026 |issn=1095-9203 |pmid=22246768 |s2cid=14113328 |last16=Emberson |first16=Lisa |last17=Streets |first17=David |last18=Ramanathan |first18=V. |last19=Hicks |first19=Kevin |last20=Oanh |first20=N. T. Kim |last21=Milly |first21=George |last22=Williams |first22=Martin |last23=Demkine |first23=Volodymyr |last24=Fowler |first24=David}}

Methane is extremely flammable and may form explosive mixtures with air. Methane gas explosions are responsible for many deadly mining disasters.{{cite news |last=Dozolme |first=Philippe |title=Common Mining Accidents |work=About.com Money |url=http://mining.about.com/od/Accidents/a/Common-Mining-Accidents.htm |url-status=live |archive-url=https://web.archive.org/web/20121111173049/http://mining.about.com/od/Accidents/a/Common-Mining-Accidents.htm |archive-date=November 11, 2012 |access-date=November 7, 2012 |publisher=About.com}} A methane gas explosion was the cause of the Upper Big Branch coal mine disaster in West Virginia on April 5, 2010, killing 29.{{cite web |last1=Messina |first1=Lawrence |last2=Bluestein |first2=Greg |name-list-style=amp |date=April 8, 2010 |title=Fed official: Still too soon for W.Va. mine rescue |url=https://news.yahoo.com/s/ap/us_mine_explosion |url-status=live |archive-url=https://web.archive.org/web/20100408145839/http://news.yahoo.com/s/ap/us_mine_explosion |archive-date=April 8, 2010 |access-date=April 8, 2010 |publisher=News.yahoo.com}} Natural gas accidental release has also been a major focus in the field of safety engineering, due to past accidental releases that concluded in the formation of jet fire disasters.{{cite journal |last1=Osman |first1=Karim |last2=Geniaut |first2=Baptiste |last3=Herchin |first3=Nicolas |last4=Blanchetierre |first4=Vincent |date=2015 |title=A review of damages observed after catastrophic events experienced in the mid-stream gas industry compared to consequences modelling tools |url=https://www.icheme.org/media/8675/paper-11-hazards-25.pdf |journal=Symposium Series |volume=160 |issue=25 |access-date=1 July 2022}}{{cite journal |last1=Casal |first1=Joaquim |last2=Gómez-Mares |first2=Mercedes |last3=Muñoz |first3=Miguel |last4=Palacios |first4=Adriana |date=2012 |title=Jet Fires: a "Minor" Fire Hazard? |url=https://www.aidic.it/cet/12/26/003.pdf |journal=Chemical Engineering Transactions |volume=26 |pages=13–20 |doi=10.3303/CET1226003 |access-date=1 July 2022}}

The 2015–2016 methane gas leak in Aliso Canyon, California was considered to be the worst in terms of its environmental effect in American history.{{Cite news |title=Porter Ranch gas leak permanently capped, officials say |newspaper=Los Angeles Times |url=http://www.latimes.com/local/lanow/la-me-ln-porter-ranch-gas-leak-permanently-capped-20160218-story.html |access-date=February 18, 2016}}{{cite web |first=Matt |last=McGrath |date=February 26, 2016 |title=California methane leak 'largest in US history' |url=https://www.bbc.co.uk/news/science-environment-35659947 |accessdate=February 26, 2016 |work=BBC News}}{{cite web |title=The Massive Methane Blowout In Aliso Canyon Was The Largest in U.S. History |url=http://archive.thinkprogress.org/the-massive-methane-blowout-in-aliso-canyon-was-the-largest-in-u-s-history-7f2984d078b0/ |last=Davila Fragoso |first=Alejandro |access-date=February 26, 2016 |website=ThinkProgress|date=February 26, 2016 }} It was also described as more damaging to the environment than Deepwater Horizon's leak in the Gulf of Mexico.{{cite news |first=Tim |last=Walker |date=January 2, 2016 |title=California methane gas leak 'more damaging than Deepwater Horizon disaster' |newspaper=The Independent |url=https://www.independent.co.uk/news/world/americas/california-methane-gas-leak-more-damaging-than-deepwater-horizon-disaster-a6794251.html |url-status=live |url-access=limited |accessdate=July 6, 2017 |archive-url=https://web.archive.org/web/20160104165145/http://www.independent.co.uk/news/world/americas/california-methane-gas-leak-more-damaging-than-deepwater-horizon-disaster-a6794251.html |archive-date=2016-01-04}}

In May 2023 The Guardian published a report blaming Turkmenistan as the worst in the world for methane super emitting. The data collected by Kayrros researchers indicate that two large Turkmen fossil fuel fields leaked 2.6 million and 1.8 million metric tonnes of methane in 2022 alone, pumping the {{CO2}} equivalent of 366 million tonnes into the atmosphere, surpassing the annual {{CO2}} emissions of the United Kingdom.{{Cite news |last1=Carrington |first1=Damian |date=May 9, 2023 |title='Mind-boggling' methane emissions from Turkmenistan revealed |language=en |newspaper=The Guardian |url=https://www.theguardian.com/world/2023/may/09/mind-boggling-methane-emissions-from-turkmenistan-revealed |access-date=2023-05-09}}

Methane is also an asphyxiant if the oxygen concentration is reduced to below about 16% by displacement, as most people can tolerate a reduction from 21% to 16% without ill effects. The concentration of methane at which asphyxiation risk becomes significant is much higher than the 5–15% concentration in a flammable or explosive mixture. Methane off-gas can penetrate the interiors of buildings near landfills and expose occupants to significant levels of methane. Some buildings have specially engineered recovery systems below their basements to actively capture this gas and vent it away from the building.{{cn|date=November 2024}}

{{main|Extraterrestrial atmosphere}}

{{missing|section|where extraterrestrial abiotic methane comes from (Big Bang? supernova? mineral deposits reacting?)|date=June 2024}}

Methane is abundant in many parts of the Solar System and potentially could be harvested on the surface of another Solar System body (in particular, using methane production from local materials found on Mars{{Cite journal | doi = 10.1061/(ASCE)AS.1943-5525.0000201| title = Integrated Mars in Situ Propellant Production System| journal = Journal of Aerospace Engineering| volume = 26| pages = 43–56| year = 2013| last1 = Zubrin | first1 = R. M. | last2 = Muscatello | first2 = A. C. | last3 = Berggren | first3 = M. }} or Titan), providing fuel for a return journey.{{cite web |url=https://science.nasa.gov/science-news/science-at-nasa/2007/04may_methaneblast/ |title=Methane Blast |date=May 4, 2007 |publisher=NASA |access-date=July 7, 2012 |archive-date=November 16, 2019 |archive-url=https://web.archive.org/web/20191116170724/https://science.nasa.gov/science-news/science-at-nasa/2007/04may_methaneblast/ |url-status=live }}

Negative methane, the negative ion of methane, is also known to exist in interstellar space.{{Cite journal |last=Millar |first=Thomas J. |last2=Walsh |first2=Catherine |last3=Field |first3=Thomas A. |date=2017-02-08 |title=Negative Ions in Space |url=https://pubs.acs.org/doi/10.1021/acs.chemrev.6b00480 |journal=Chemical Reviews |language=en |volume=117 |issue=3 |pages=1765–1795 |doi=10.1021/acs.chemrev.6b00480 |issn=0009-2665}} Its mechanism of formation is not fully understood.

Methane has been detected on all planets of the Solar System and most of the larger moons.{{citation needed|date=January 2021}} With the possible exception of Mars, it is believed to have come from abiotic processes.{{cite news |last=Chang |first=Kenneth |title=Hope of Methane on Mars Fades |url=https://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |date=November 2, 2012 |work=The New York Times |access-date=November 3, 2012 |archive-date=June 8, 2019 |archive-url=https://web.archive.org/web/20190608041309/https://www.nytimes.com/2012/11/03/science/space/hopes-for-methane-on-mars-deflated.html |url-status=live }}{{cite journal |title=Methane and related trace species on Mars: origin, loss, implications for life, and habitability |author1=Atreya, Sushil K. |author2=Mahaffy, Paul R. |author3=Wong, Ah-San |journal=Planetary and Space Science |year=2007 |volume=55 |issue=3 |pages=358–369 |doi=10.1016/j.pss.2006.02.005 |bibcode=2007P&SS...55..358A |hdl=2027.42/151840 |hdl-access=free}}

File:PIA19088-MarsCuriosityRover-MethaneSource-20141216.png ({{chem2|CH4}}) on Mars{{snd}} potential sources and sinks]]

The Curiosity rover has documented seasonal fluctuations of atmospheric methane levels on Mars. These fluctuations peaked at the end of the Martian summer at 0.6 parts per billion.{{cite web |last1=Brown |first1=Dwayne |last2=Wendel |first2=JoAnna |last3=Steigerwald |first3=Bill |last4=Jones |first4=Nancy |last5=Good |first5=Andrew |title=Release 18-050 – NASA Finds Ancient Organic Material, Mysterious Methane on Mars |url=https://www.nasa.gov/press-release/nasa-finds-ancient-organic-material-mysterious-methane-on-mars |date=June 7, 2018 |website=NASA |access-date=June 7, 2018 |archive-date=June 7, 2018 |archive-url=https://web.archive.org/web/20180607181653/https://www.nasa.gov/press-release/nasa-finds-ancient-organic-material-mysterious-methane-on-mars/ |url-status=live }}{{cite web |author=NASA |title=Ancient Organics Discovered on Mars – video (03:17) |url=https://www.youtube.com/watch?v=a0gsz8EHiNc |date=June 7, 2018 |website=NASA |access-date=June 7, 2018 |archive-date=June 7, 2018 |archive-url=https://web.archive.org/web/20180607220111/https://www.youtube.com/watch?v=a0gsz8EHiNc |url-status=live }}{{cite web |last=Wall |first=Mike |title=Curiosity Rover Finds Ancient 'Building Blocks for Life' on Mars |url=https://www.space.com/40819-mars-methane-organics-curiosity-rover.html |date=June 7, 2018 |website=Space.com |access-date=June 7, 2018 |archive-date=June 7, 2018 |archive-url=https://web.archive.org/web/20180607191720/https://www.space.com/40819-mars-methane-organics-curiosity-rover.html |url-status=live }}{{cite news |last=Chang |first=Kenneth |title=Life on Mars? Rover's Latest Discovery Puts It 'On the Table' – The identification of organic molecules in rocks on the red planet does not necessarily point to life there, past or present, but does indicate that some of the building blocks were present. |url=https://www.nytimes.com/2018/06/07/science/mars-nasa-life.html |date=June 7, 2018 |work=The New York Times |access-date=June 8, 2018 |archive-date=June 8, 2018 |archive-url=https://web.archive.org/web/20180608050854/https://www.nytimes.com/2018/06/07/science/mars-nasa-life.html |url-status=live }}{{cite journal |last=Voosen |first=Paul |title=NASA rover hits organic pay dirt on Mars |date=June 7, 2018 |journal=Science | doi = 10.1126/science.aau3992 |s2cid=115442477 }}{{cite journal |last=ten Kate |first=Inge Loes |title=Organic molecules on Mars |date=June 8, 2018 |journal=Science |volume=360 |issue=6393 |pages=1068–1069 |doi=10.1126/science.aat2662| pmid=29880670 |bibcode=2018Sci...360.1068T |hdl=1874/366378 |s2cid=46952468 |hdl-access=free }}{{cite journal |author=Webster, Christopher R. |display-authors=etal |title=Background levels of methane in Mars' atmosphere show strong seasonal variations |date=June 8, 2018 |journal=Science |volume=360 |issue=6393 |pages=1093–1096 |doi=10.1126/science.aaq0131 |pmid=29880682 |bibcode=2018Sci...360.1093W |doi-access=free }}{{cite journal |author=Eigenbrode, Jennifer L. |author-link1=Jennifer Eigenbrode|display-authors=etal |title=Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars |date=June 8, 2018 |journal=Science |volume=360 |issue=6393 |pages=1096–1101 |doi=10.1126/science.aas9185 |pmid=29880683 |bibcode=2018Sci...360.1096E |doi-access=free |hdl=10044/1/60810 |hdl-access=free }}

Methane has been proposed as a possible rocket propellant on future Mars missions due in part to the possibility of synthesizing it on the planet by in situ resource utilization.{{cite news |url=http://www.spaceflightinsider.com/organizations/space-exploration-technologies/elon-musk-shows-off-interplanetary-transport-system/ |title=Elon Musk Shows Off Interplanetary Transport System |publisher=Spaceflight Insider |last=Richardson |first=Derek |date=September 27, 2016 |access-date=October 3, 2016 |archive-date=October 1, 2016 |archive-url=https://web.archive.org/web/20161001225649/http://www.spaceflightinsider.com/organizations/space-exploration-technologies/elon-musk-shows-off-interplanetary-transport-system/ |url-status=live }} An adaptation of the Sabatier methanation reaction may be used with a mixed catalyst bed and a reverse water-gas shift in a single reactor to produce methane and oxygen from the raw materials available on Mars, utilizing water from the Martian subsoil and carbon dioxide in the Martian atmosphere.

Methane could be produced by a non-biological process called serpentinization{{efn|name=serpentinization}} involving water, carbon dioxide, and the mineral olivine, which is known to be common on Mars.{{cite journal |author1=Oze, C. |author2=Sharma, M. |title=Have olivine, will gas: Serpentinization and the abiogenic production of methane on Mars |journal=Geophysical Research Letters |year=2005 |volume=32 |issue=10 |page=L10203 |doi=10.1029/2005GL022691 |bibcode=2005GeoRL..3210203O|s2cid=28981740 |doi-access=free }}

File:PIA22481-SaturnMoon-Titan-Lakes-20170911.jpg

Methane has been detected in vast abundance on Titan, the largest moon of Saturn. It comprises a significant portion of its atmosphere and also exists in a liquid form on its surface, where it comprises the majority of the liquid in Titan's vast lakes of hydrocarbons, the second largest of which is believed to be almost pure methane in composition.{{cite web | url = http://www.jpl.nasa.gov/news/news.php?feature=6440 | title = Cassini Explores a Methane Sea on Titan | date = 2016-04-26 | website = Jet Propulsion Laboratory News }}

The presence of stable lakes of liquid methane on Titan, as well as the surface of Titan being highly chemically active and rich in organic compounds, has led scientists to consider the possibility of life existing within Titan's lakes, using methane as a solvent in the place of water for Earth-based life{{cite book |author1=Committee on the Limits of Organic Life in Planetary Systems |author2=Committee on the Origins and Evolution of Life |author3=National Research Council |year=2007 |url=http://books.nap.edu/openbook.php?record_id=11919&page=74 |title=The Limits of Organic Life in Planetary Systems |publisher=The National Academies Press |page=74|doi=10.17226/11919 |isbn=978-0-309-10484-5 }} and using hydrogen in the atmosphere to derive energy with acetylene.{{cite journal|journal = Icarus|volume= 178|issue = 1|pages = 274–276|date= 2005|doi = 10.1016/j.icarus.2005.05.018|title = Possibilities for methanogenic life in liquid methane on the surface of Titan|last1=McKay |first1=C. P. |last2=Smith |first2=H. D. |bibcode=2005Icar..178..274M|url= https://zenodo.org/record/1259025}}

File:ETH-BIB-Volta, Alessandro (1745-1827)-Portrait-Portr 02303.tif]]

The discovery of methane is credited to Italian physicist Alessandro Volta, who characterized numerous properties including its flammability limit and origin from decaying organic matter.Volta, Alessandro (1777) [https://www.europeana.eu/portal/en/record/9200332/BibliographicResource_3000123618397.html Lettere del Signor Don Alessandro Volta ... Sull' Aria Inflammable Nativa Delle Paludi] {{Webarchive|url=https://web.archive.org/web/20181106200036/https://www.europeana.eu/portal/en/record/9200332/BibliographicResource_3000123618397.html|date=November 6, 2018}} [Letters of Signor Don Alessandro Volta ... on the flammable native air of the marshes], Milan, Italy: Giuseppe Marelli.

Volta was initially motivated by reports of inflammable air present in marshes by his friend Father Carlo Guiseppe Campi. While on a fishing trip to Lake Maggiore straddling Italy and Switzerland in November 1776, he noticed the presence of bubbles in the nearby marshes and decided to investigate. Volta collected the gas rising from the marsh and demonstrated that the gas was inflammable.{{Cite book |last=Sethi |first=Anand Kumar |url=https://books.google.com/books?id=WCrRDAAAQBAJ |title=The European Edisons: Volta, Tesla, and Tigerstedt |date=2016-08-09 |publisher=Springer |isbn=978-1-137-49222-7 |language=en}}

Volta notes similar observations of inflammable air were present previously in scientific literature, including a letter written by Benjamin Franklin.{{Cite web |title=Founders Online: From Benjamin Franklin to Joseph Priestley, 10 April 1774 |url=https://founders.archives.gov/documents/Franklin/01-21-02-0078 |access-date=2024-09-27 |website=founders.archives.gov |language=en}}

Following the Felling mine disaster of 1812 in which 92 men perished, Sir Humphry Davy established that the feared firedamp was in fact largely methane.{{Cite book| publisher = London, Whittaker and Co.| last = Holland| first = John| title = The history and description of fossil fuel, the collieries, and coal trade of Great Britain| accessdate = May 16, 2021| date = 1841| url = http://archive.org/details/historyanddescr01hollgoog|pages=271–272}}

The name "methane" was coined in 1866 by the German chemist August Wilhelm von Hofmann.{{cite journal|jstor=112588|author=Hofmann, A. W.|year=1866|url=http://rspl.royalsocietypublishing.org/content/15/54.full.pdf+html|title=On the action of trichloride of phosphorus on the salts of the aromatic monoamines|journal=Proceedings of the Royal Society of London|volume=15|pages=55–62|access-date=June 14, 2016|archive-date=May 3, 2017|archive-url=https://web.archive.org/web/20170503142331/http://rspl.royalsocietypublishing.org/content/15/54.full.pdf+html|url-status=live}}; see footnote on pp. 57–58McBride, James Michael (1999) [http://chem125-oyc.webspace.yale.edu/125/history99/5Valence/Nomenclature/alkanenames.html "Development of systematic names for the simple alkanes"]. Chemistry Department, Yale University (New Haven, Connecticut). {{Webarchive|url=https://web.archive.org/web/20120316080546/https://webspace.yale.edu/chem125/125/history99/5Valence/Nomenclature/alkanenames.html |date=March 16, 2012 }} The name was derived from methanol.

Etymologically, the word methane is coined from the chemical suffix "-ane", which denotes substances belonging to the alkane family; and the word methyl, which is derived from the German {{lang|de|Methyl}} (1840) or directly from the French {{lang|fr|méthyle}}, which is a back-formation from the French {{lang|fr|méthylène}} (corresponding to English "methylene"), the root of which was coined by Jean-Baptiste Dumas and Eugène Péligot in 1834 from the Greek {{lang|grc|μέθυ}} {{lang|grc-Latn|méthy}} (wine) (related to English "mead") and {{lang|grc|ὕλη}} {{lang|grc-Latn|hýlē}} (meaning "wood"). The radical is named after this because it was first detected in methanol, an alcohol first isolated by distillation of wood. The chemical suffix -ane is from the coordinating chemical suffix -ine which is from Latin feminine suffix -ina which is applied to represent abstracts. The coordination of "-ane", "-ene", "-one", etc. was proposed in 1866 by German chemist August Wilhelm von Hofmann.{{OEtymD|methane}}

The abbreviation {{chem2|CH4}}-C can mean the mass of carbon contained in a mass of methane, and the mass of methane is always 1.33 times the mass of {{chem2|CH4}}-C.{{Cite web |last=Jayasundara |first=Susantha |date=December 3, 2014 |title=Is there is any difference in expressing greenhouse gases as CH4Kg/ha and CH4-C Kg/ha? |url=https://www.researchgate.net/post/Is_there_is_any_difference_in_expressing_greenhouse_gases_as_CH4Kg_ha_and_CH4-C_Kg_ha |access-date=August 26, 2020 |website=ResearchGate |archive-date=October 1, 2021 |archive-url=https://web.archive.org/web/20211001032525/https://www.researchgate.net/post/Is_there_is_any_difference_in_expressing_greenhouse_gases_as_CH4Kg_ha_and_CH4-C_Kg_ha |url-status=live }}{{Cite web |date=November 26, 2019 |title=User's Guide For Estimating Carbon Dioxide, Methane, And Nitrous Oxide Emissions From Agriculture Using The State Inventory Tool |url=https://www.epa.gov/sites/production/files/2017-12/documents/ag_module_users_guide.pdf |access-date=August 26, 2020 |website=US EPA |archive-date=October 1, 2021 |archive-url=https://web.archive.org/web/20211001032523/https://www.epa.gov/sites/default/files/2017-12/documents/ag_module_users_guide.pdf |url-status=live }} {{chem2|CH4}}-C can also mean the methane-carbon ratio, which is 1.33 by mass.{{Cite web |title=What does CH4-C mean? – Definition of CH4-C – CH4-C stands for Methane-carbon ratio |url=http://acronymsandslang.com/definition/7726964/CH4_C-meaning.html |access-date=August 26, 2020 |website=acronymsandslang.com |archive-date=April 11, 2015 |archive-url=https://web.archive.org/web/20150411192614/http://acronymsandslang.com/definition/7726964/CH4_C-meaning.html |url-status=live }} Methane at scales of the atmosphere is commonly measured in teragrams (Tg {{chem2|CH4}}) or millions of metric tons (MMT {{chem2|CH4}}), which mean the same thing.{{Cite web |last=Office of Air and Radiation, US EPA |date=October 7, 1999 |title=U.S. Methane Emissions 1990–2020: Inventories, Projections, and Opportunities for Reductions (EPA 430-R-99-013) |url=https://www.ourenergypolicy.org/wp-content/uploads/2013/07/EPA-Methane-Emissions-1990-2020.pdf |access-date=August 26, 2020 |website=ourenergypolicy.org |archive-date=October 26, 2020 |archive-url=https://web.archive.org/web/20201026213938/https://www.ourenergypolicy.org/wp-content/uploads/2013/07/EPA-Methane-Emissions-1990-2020.pdf |url-status=live }} Other standard units are also used, such as nanomole (nmol, one billionth of a mole), mole (mol), kilogram, and gram.

{{Div col|colwidth=30em|content=

• 2007 Zasyadko mine disaster
• Abiogenic petroleum origin
• Aerobic methane production
• Anaerobic digestion
• Anaerobic respiration
• Arctic methane emissions
• Atmospheric methane
• Biogas
• Coal Oil Point seep field
• Energy density
• Fugitive gas emissions
• Global Methane Initiative
• Thomas Gold
• Halomethane, halogenated methane derivatives.
• Hydrogen Cycle
• Industrial gas
• Lake Kivu (more general: limnic eruption)
• List of straight-chain alkanes
• Methanation
• Methane emissions
• Methane on Mars:
• atmosphere
• climate
• Methanogen, archaea that produce methane.
• Methanogenesis, microbes that produce methane.
• Methanotroph, bacteria that grow with methane.
• Methyl group, a functional group related to methane.

}}

{{notelist

| notes = {{efn |name=serpentinization |There are many serpentinization reactions. Olivine is a solid solution between forsterite and fayalite whose general formula is {{chem2|(Fe,Mg)2SiO4}}. The reaction producing methane from olivine can be written as: Forsterite + Fayalite + Water + Carbonic acid → Serpentine + Magnetite + Methane , or (in balanced form):

:{{chem2|18 Mg2SiO4 + 6 Fe2SiO4 + 26 H2O + CO2 → 12 Mg3Si2O5(OH)4 + 4 Fe3O4 + CH4}} }}}}

{{Reflist|refs=

{{Cite journal |doi= 10.1016/j.cplett.2011.10.020 |title=Comparative study of the hypercoordinate carbonium ions and their boron analogs: A challenge for spectroscopists |journal=Chemical Physics Letters |volume=517 |issue=1 |pages=1–8 |year=2011 |last1=Rasul |first1=G. |last2=Surya Prakash |first2=G.K. |last3=Olah |first3=G.A. |bibcode=2011CPL...517....1R}}

}}

• {{cite book |ref=Haynes| editor= Haynes, William M. | date = 2016| title = CRC Handbook of Chemistry and Physics | edition = 97th | publisher = CRC Press | isbn = 9781498754293}}

{{Commons}}

{{Wiktionary|methane}}

• [http://www.periodicvideos.com/videos/mv_methane.htm Methane] at The Periodic Table of Videos (University of Nottingham)
• [http://www.inchem.org/documents/icsc/icsc/eics0291.htm International Chemical Safety Card 0291]
• [https://web.archive.org/web/20040206225737/https://marine.usgs.gov/fact-sheets/gas-hydrates/title.html Gas (Methane) Hydrates – A New Frontier] – United States Geological Survey (archived 6 February 2004)
• {{cite journal|doi=10.1016/S0920-5861(00)00456-9|title=Catalytic conversion of methane to more useful chemicals and fuels: A challenge for the 21st century|journal=Catalysis Today|volume=63|issue=2–4|pages=165–174|year=2000|last1=Lunsford|first1=Jack H.}}
• [https://www.cdc.gov/niosh/mining/UserFiles/works/pdfs/2006-127.pdf CDC – Handbook for Methane Control in Mining] (PDF)

{{Alkanes}}

{{Fuel gas}}

{{Molecules detected in outer space}}

{{Hydrides by group}}

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