Wikipedia:WikiProject Chemicals/Chembox validation/VerifiedDataSandbox and Methane: Difference between pages

{{Short description|Hydrocarbon compound (CH₄) in natural gas}}

{{Hatnote group|

{{Distinguish|Ethane|ETHANE}}

{{Redirect|CH4}}

}}

{{Pp-move}}

{{Use mdy dates|date=November 2021}}

| verifiedrevid = 464371375

| Name =

| ImageSize = 170

| ImageCaptionR1 = {{legend|black|Carbon, C}}{{legend|white|Hydrogen, H}}

| PIN = Methane<ref name=iupac2013>{{cite book|title = Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book)|publisher = [[Royal Society of Chemistry|The Royal Society of Chemistry]]|date = 2014|location = Cambridge|pages = 3–4|doi = 10.1039/9781849733069-FP001|isbn = 978-0-85404-182-4|quote = Methane is a retained name (see P-12.3) that is preferred to the systematic name ‘carbane’, a name never recommended to replace methane, but used to derive the names ‘carbene’ and ‘carbyne’ for the radicals H₂C^2• and HC^3•, respectively.|chapter = Front Matter}}</ref>

| SystematicName = Carbane (never recommended<ref name=iupac2013 />)

| OtherNames = {{ubl|Carbon tetrahydride|Carburetted hydrogen|Hydrogen carbide|Marsh gas|Methyl hydride|Natural gas}}

| IUPACName =

| CASNo = 74-82-8

| CASNo_Ref = {{cascite|correct|CAS}}

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = OP0UW79H66

| PubChem = 297

| ChemSpiderID = 291

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| EINECS = 200-812-7

| UNNumber = 1971

| KEGG = C01438

| KEGG_Ref = {{keggcite|confirmed|kegg}}

| MeSHName = Methane

| ChEBI = 16183

| ChEBI_Ref = {{ebicite|correct|EBI}}

| ChEMBL = 17564

| ChEMBL_Ref = {{ebicite|correct|EBI}}

| RTECS = PA1490000

| Beilstein = 1718732

| Gmelin = 59

| 3DMet = B01453

| SMILES = C

| StdInChI = 1S/CH4/h1H4

| StdInChI_Ref = {{stdinchicite|correct|chemspider}}

| StdInChIKey = VNWKTOKETHGBQD-UHFFFAOYSA-N

| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

}}

| C=1 | H=4

| Appearance = Colorless gas

| Odor = Odorless

| Density = {{ubl|0.657 kg/m³ (gas, 25 °C, 1 atm)|0.717 kg/m³ (gas, 0 °C, 1 atm)<ref>{{cite web|title=Gas Encyclopedia|url=http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=41|access-date=November 7, 2013|archive-date=December 26, 2018|archive-url=https://web.archive.org/web/20181226083050/https://encyclopedia.airliquide.com/methane?GasID=41|url-status=live}}</ref>

| 422.8 g/L (liquid, −162 °C)<ref name=crc>[[#Haynes|Haynes]], p. 3.344</ref>

}}

| MeltingPtC = −182.456

| BoilingPtC = −161.5

| MeltingPt_ref = <ref name=crc/>

| BoilingPt_ref = <ref name=crc/>

| CriticalTP = {{cvt|190.56|K}}, {{cvt|4.5992|MPa|atm}}

| Solubility = 22.7 mg/L<ref>[[#Haynes|Haynes]], p. 5.156</ref>

| SolubleOther = Soluble in [[ethanol]], [[diethyl ether]], [[benzene]], [[toluene]], [[methanol]], [[acetone]] and insoluble in [[water]]

| ConjugateAcid = [[Methanium]]

| ConjugateBase = [[Methyl anion]]

| LogP = 1.09

| HenryConstant = 14 nmol/(Pa·kg)

| MagSus = −17.4{{e|−6}} cm³/mol<ref>[[#Haynes|Haynes]], p. 3.578</ref>

}}

| Section3 = {{Chembox Structure

| MolShape = [[Tetrahedral molecular geometry|Tetrahedral]] at [[carbon]] atom

| Dipole = 0{{nbsp}}D

| PointGroup = T_d

}}

| Section4 = {{Chembox Thermochemistry

| Thermochemistry_ref = <ref>[[#Haynes|Haynes]], pp. 5.26, 5.67</ref>

| DeltaGfree = −50.5 kJ/mol

| DeltaHf = −74.6 kJ/mol

| DeltaHc = −891 kJ/mol

| Entropy = 186.3 J/(K·mol)

| HeatCapacity = 35.7 J/(K·mol)

}}

| Section7 = {{Chembox Hazards

| Hazards_ref = <ref>{{cite web|title=Safety Datasheet, Material Name: Methane|url=http://www.chemadvisor.com/Matheson/database/msds/00244226000800003.PDF|publisher=Metheson Tri-Gas Incorporated|access-date=December 4, 2011|location=US|date=December 4, 2009|url-status=dead|archive-url=https://web.archive.org/web/20120604162221/http://www.chemadvisor.com/Matheson/database/msds/00244226000800003.PDF|archive-date=June 4, 2012}}</ref>

| GHSPictograms = {{GHS02}}

| GHSSignalWord = Danger

| HPhrases = {{H-phrases|220}}

| PPhrases = {{P-phrases|210}}

| NFPA-H = 2

| NFPA-F = 4

| NFPA-R = 0

| NFPA-S = SA

| FlashPtC = −188

| AutoignitionPtC = 537

| ExploLimits = 4.4–17%

}}<ref>{{cite web|url=http://cameochemicals.noaa.gov/chemical/8823|title=METHANE|author=NOAA Office of Response and Restoration, US GOV|website=noaa.gov|access-date=March 20, 2015|archive-date=January 9, 2019|archive-url=https://web.archive.org/web/20190109075841/https://cameochemicals.noaa.gov/chemical/8823|url-status=live}}</ref>

| Section8 = {{Chembox Related

| OtherFunction_label = alkanes

| OtherFunction = {{ubl|[[Ethane]]|[[Propane]]|[[Butane]]}}

| OtherCompounds = {{ubl|[[Silane]]|[[Germane]]|[[Stannane]]|[[Plumbane]]}}

'''Methane''' ({{IPAc-en|US|ˈ|m|ɛ|θ|eɪ|n}} {{Respell|METH|ayn}}, {{IPAc-en|UK|ˈ|m|iː|θ|eɪ|n}} {{Respell|MEE|thayn}}) is a [[chemical compound]] with the [[chemical formula]] {{chem2|CH4}} (one [[carbon]] atom bonded to four [[hydrogen]] atoms). It is a [[group-14 hydride]], the simplest [[alkane]], and the main constituent of [[natural gas]]. The abundance of methane on [[Earth]] makes it an economically attractive [[fuel]], although capturing and storing it is hard because it is a [[gas]] at [[standard temperature and pressure]].

Naturally occurring methane is found both below ground and under the [[seafloor]] and is formed by both geological and biological processes. The largest [[reservoir]] of methane is under the seafloor in the form of [[methane clathrate]]s. When methane reaches the surface and the [[Atmosphere of Earth|atmosphere]], it is known as [[atmospheric methane]].<ref name="Khalil-1999">{{Cite journal|last1=Khalil|first1=M. A. K.|year=1999|title=Non-Co2 Greenhouse Gases in the Atmosphere|journal=[[Annual Review of Energy and the Environment]]|volume=24|pages=645–661|doi=10.1146/annurev.energy.24.1.645|doi-access=}}</ref>

The Earth's atmospheric methane concentration [[Methane emissions|has increased]] by about 160% since 1750, with the overwhelming percentage caused by human activity.<ref name="UNEP_2022">{{cite report |url=https://wedocs.unep.org/bitstream/handle/20.500.11822/41108/methane_2030_SPM.pdf |title=Global Methane Assessment |date=2022 |location=Nairobi |pages=12 |access-date=March 15, 2023 |work=United Nations Environment Programme and Climate and Clean Air Coalition}}</ref> It accounted for 20% of the total [[radiative forcing]] from all of the long-lived and globally mixed [[greenhouse gas]]es, according to the 2021 [[Intergovernmental Panel on Climate Change]] report.<ref name="Technical summary2">{{cite web|title=Climate Change 2021. The Physical Science Basis. Summary for Policymakers. Working Group I contribution to the WGI Sixth Assessment Report of the Intergovernmental Panel on Climate Change|url=https://www.ipcc.ch/assessment-report/ar6/|url-status=dead|archive-url=https://web.archive.org/web/20210822165901/https://www.ipcc.ch/assessment-report/ar6/|archive-date=August 22, 2021|website=IPCC|publisher=The Intergovernmental Panel on Climate Change|access-date=August 22, 2021}}</ref> Strong, rapid and sustained reductions in methane emissions could limit near-term warming and improve air quality by reducing global surface ozone.<ref>[https://www.ipcc.ch/report/ar6/syr/downloads/report/IPCC_AR6_SYR_SPM.pdf IPCC, 2023: Summary for Policymakers]. In: Climate Change 2023: Synthesis Report. A Report of the Intergovernmental Panel on Climate Change. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, page 26, section C.2.3</ref>

Methane has also been detected on other planets, including [[Mars]], which has implications for [[astrobiology]] research.<ref name="Etiope-2013">{{Cite journal|last1=Etiope|first1=Giuseppe|last2=Lollar|first2=Barbara Sherwood|date=2013|title=Abiotic Methane on Earth|journal=Reviews of Geophysics|volume=51|issue=2|pages=276–299|doi=10.1002/rog.20011|bibcode=2013RvGeo..51..276E| s2cid=56457317 }}</ref>

==Properties and bonding==

[[File:Covalent.svg|left|thumb|upright=1|[[Covalently bonded]] hydrogen and carbon in a molecule of methane.]]Methane is a [[tetrahedral molecular geometry|tetrahedral]] molecule with four equivalent [[Carbon–hydrogen bond|C–H bonds]]. Its [[Electron configuration|electronic structure]] is described by four bonding molecular orbitals (MOs) resulting from the overlap of the valence orbitals on [[Carbon|C]] and [[Hydrogen|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.<ref>{{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 }}</ref> It does absorb visible light, especially at the red end of the spectrum, due to [[overtone band]]s, 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.<ref>{{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 }}</ref>

The familiar smell of natural gas as used in homes is achieved by the addition of an [[odorizer|odorant]], usually blends containing [[tert-butylthiol|''tert''-butylthiol]], as a safety measure. Methane has a boiling point of −161.5&nbsp;[[Degree Celsius|°C]] at a pressure of one [[Atmosphere (unit)|atmosphere]].<ref name=crc/> As a gas, it is [[flammable]] over a range of concentrations (5.4%–17%) in air at [[standard pressure]].

Solid methane exists in several [[Polymorphism (materials science)|modifications]]. Presently nine are known.<ref name="BiniPratesi">{{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&nbsp;GPa | journal = Physical Review B | volume = 55 | issue = 22 | pages = 14800–14809 | doi=10.1103/physrevb.55.14800 | bibcode = 1997PhRvB..5514800B }}</ref> Cooling methane at normal pressure results in the formation of methane&nbsp;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&nbsp;I, i.e. methane molecules may rotate freely. Therefore, it is a [[plastic crystal]].<ref>{{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 }}</ref>

==Chemical reactions==

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

===Selective oxidation===

Partial [[Redox|oxidation]] of methane to [[methanol]] ([[Carbon|C]][[Hydrogen|H]]₃[[Oxygen|O]][[Hydrogen|H]]), 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.<ref>{{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}}</ref> Some homogeneously [[Catalysis|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 [[Methane functionalization#The Catalytica system|Catalytica system]], copper [[zeolite]]s, and iron zeolites stabilizing the [[alpha-oxygen]] active site.<ref>{{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}}</ref>

One group of [[bacteria]] catalyze methane oxidation with [[nitrite]] as the [[Oxidizing agent|oxidant]] in the absence of [[oxygen]], giving rise to the so-called [[anaerobic oxidation of methane]].<ref>

{{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

</ref>

===Acid–base reactions===

Like other [[hydrocarbon]]s, methane is an extremely [[weak acid]]. Its [[pKa|p''K''_a]] in [[Dimethyl sulfoxide|DMSO]] is estimated to be 56.<ref>{{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 }}</ref> It cannot be [[Deprotonation|deprotonated]] in solution, but the [[conjugate base]] is known in forms such as [[methyllithium]].

A variety of [[cation|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 [[list of interstellar and circumstellar molecules|detected in outer space]]. Methanium can also be produced as diluted solutions from methane with [[superacid]]s. [[Cation]]s with higher charge, such as {{chem2|CH6(2+)}} and {{chem2|CH7(3+)}}, have been studied theoretically and conjectured to be stable.<ref name=Rasul/>

Despite the [[Bond strength|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]]).<ref>{{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 }}</ref>

===Combustion===

[[File: The fire within her.jpg|alt=A young woman holding a flame in her hands|thumb|Methane bubbles can be burned on a wet hand without injury.]]

Methane's [[heat of combustion]] is 55.5 MJ/kg.<ref>[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.</ref> [[Combustion]] of methane is a multiple step reaction summarized as follows:

:{{chem2|CH4 + 2 O2 → CO2 + 2 H2O}}

:(Δ''H'' = −891 [[kilojoule|kJ]]/[[mole (unit)|mol]], at standard conditions)

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

===Methane radical reactions===

Given appropriate conditions, methane reacts with [[halogen]] [[Radical (chemistry)|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.<ref>{{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}}</ref> 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.

==Uses==

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. [[Pipeline transport|Gas pipelines]] distribute large amounts of natural gas, of which methane is the principal component.

===Fuel===

Methane is used as a [[fuel]] for ovens, homes, water heaters, kilns, automobiles,<ref>{{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}}</ref><ref name="Cornell-2008">{{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}}</ref> 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 [[Boiler (power generation)|steam generator]]. Compared to other [[fossil fuel|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 [[megajoule]]s per cubic meter, or 1,000 [[British thermal unit|BTU]] per [[standard cubic foot]]. [[Liquefied natural gas]] (LNG) is predominantly methane ({{chem2|CH4}}) converted into liquid form for ease of storage or transport.

==== Rocket propellant ====

Refined '''liquid methane'''<!-- bolded per [[WP:MOSBOLD]] as a redirect target --> as well as LNG is [[Liquid rocket propellants#Bipropellants|used as]] a [[rocket fuel]],<ref name="aiaa2004">

{{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}}</ref> when combined with [[liquid oxygen]], as in the [[TQ-12]], [[BE-4]], [[Raptor (rocket engine family)|Raptor]], and [[YF-215]] engines.<ref>{{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.}}</ref> Due to the similarities between methane and LNG such engines are commonly grouped together under the term ''methalox''.

As a [[Liquid-propellant rocket|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]].<ref name=pbt20140219>{{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}}</ref><ref name=nsf20140307>{{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}}</ref> 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&nbsp;K) nearly compatible with [[liquid oxygen]] (54–90&nbsp;K). The fuel currently sees use in operational launch vehicles such as [[Zhuque-2]] and [[Vulcan Centaur|Vulcan]] as well as in-development launchers such as [[SpaceX Starship|Starship]], [[Rocket Lab Neutron|Neutron]], and [[Terran R]].<ref>{{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 }}</ref>

===Chemical feedstock===

[[Natural gas]], which is mostly composed of methane, is used to produce hydrogen gas on an industrial scale. [[Steam reforming|Steam methane reforming]] (SMR), or simply known as steam reforming, is the standard industrial method of producing commercial bulk hydrogen gas. More than 50&nbsp;million metric tons are produced annually worldwide (2013), principally from the SMR of natural gas.<ref>[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).</ref> Much of this hydrogen is used in [[petroleum]] [[Refinery|refineries]], in the production of chemicals and in food processing. Very large quantities of hydrogen are used in the [[Ammonia production|industrial synthesis of ammonia]].

At high temperatures (700–1100&nbsp;°C) and in the presence of a [[metal]]-based [[catalyst]] ([[nickel]]), steam reacts with methane to yield a mixture of [[Carbon monoxide|CO]] and [[Dihydrogen|{{chem2|H2}}]], known as "water gas" or "[[syngas]]":

:{{chem2|CH4 + H2O ⇌ CO + 3 H2}}

This reaction is strongly [[endothermic]] (consumes heat, {{math|1=Δ''H''_r =}} 206&nbsp;kJ/mol).

Additional hydrogen is obtained by the reaction of [[carbon monoxide|CO]] with water via the [[water-gas shift reaction]]:

:{{chem2|CO + H2O ⇌ CO2 + H2}}

This reaction is mildly [[exothermic]] (produces heat, {{math|1=Δ''H''_r =}} −41&nbsp;kJ/mol).

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

Hydrogen can also be produced via the direct decomposition of methane, also known as methane [[pyrolysis]], which, unlike steam reforming, produces no [[greenhouse gas]]es (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&nbsp;°C are required to break the bonds of methane to produce Hydrogen gas and solid carbon. However, through the use of a suitable catalyst the reaction temperature can be reduced to between 600&nbsp;°C - 1000&nbsp;°C depending on the chosen catalyst.<ref>{{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}}</ref> The reaction is moderately endothermic as shown in the reaction equation below.<ref>{{cite journal |last1=Lumbers |first1=Brock |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/S0360319921044438 |journal=International Journal of Hydrogen Energy |year=2022 |volume=47 |issue=37 |pages=16347–16361 |doi=10.1016/j.ijhydene.2022.03.124 |bibcode=2022IJHE...4716347L |s2cid=248018294 |access-date=10 July 2022}}</ref>

:{{chem2|CH4(g) → C(s) + 2 H2(g)}}

:({{math|1=ΔH° =}} 74.8 [[Joule per mole|kJ/mol]])

=== Refrigerant ===

As a [[refrigerant]], methane has the [[ASHRAE]] designation [[List of refrigerants#:~:text=R-50|R-50]].

==Generation==

[[File:Global Methane Budget 2017.jpg|thumb|Global methane budget (2017). Shows natural sources and sinks (green), anthropogenic sources (orange), and mixed natural and anthropogenic sources (hatched orange-green for 'biomass and biofuel burning').]]

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

=== Geological routes ===

{{See also|Biogeochemistry}}

[[File:Origins_of_Biotic_and_Abiotic_Methane.jpg|thumb|upright=1.35|Abiotic sources of methane{{examples needed|date=June 2024}} have been found in more than 20 countries and in several deep ocean regions so far.]]The two main routes for geological methane generation are (i) organic (thermally generated, or thermogenic) and (ii) inorganic ([[Abiotic component|abiotic]]).<ref name="Etiope-2013"/> Thermogenic methane occurs due to the breakup of organic matter at elevated temperatures and pressures in deep sedimentary [[Stratum|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 [[Serpentinite|serpentinization]].<ref name="Kietäväinen-2015">{{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}}</ref><ref name="Cramer-2005">{{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}}</ref>

===Biological routes===

{{Main|Methanogenesis}}

Most of Earth's methane is [[Biogenic substance|biogenic]] and is produced by [[methanogenesis]],<ref name="Lessner-2009">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}}</ref><ref name="Thiel-2018">{{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 }}</ref> a form of anaerobic respiration only known to be conducted by some members of the domain [[Archaea]].<ref name="Dean-2018-2">{{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 }}</ref> Methanogens occur in [[landfill]]s and [[Soil gas|soils]],<ref name="Serrano-Silva-2014">{{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 }}</ref> [[ruminants]] (for example, [[cattle]]),<ref name="Sirohi-2010">{{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}}</ref> the guts of termites, and the [[Anoxic waters|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 [[Coenzyme-B sulfoethylthiotransferase|methyl coenzyme M reductase]] (MCR).<ref>{{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 }}</ref>[[File:CSIRO ScienceImage 1898 Testing Sheep for Methane Production.jpg|thumb|Testing Australian sheep for exhaled methane production (2001), [[CSIRO]]]]

[[File:The Creation of Methane Within a Ruminant.svg|thumb|This image represents a ruminant, specifically a sheep, producing methane in the four stages of hydrolysis, acidogenesis, acetogenesis, and methanogenesis.]]

==== Wetlands ====

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

Wetlands are the largest natural sources of methane to the atmosphere,<ref>{{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}}</ref> accounting for approximately 20 - 30% of atmospheric methane.<ref name=":1" /> Climate change is increasing the amount of methane released from wetlands due to increased temperatures and altered rainfall patterns. This phenomeon is called ''wetland methane feedback''.<ref name=":0" />

[[Rice]] cultivation generates as much as 12% of total global methane emissions due to the long-term flooding of rice fields.<ref>{{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}}</ref>

====Ruminants====

Ruminants, such as cattle, belch methane, accounting for about 22% of the U.S. annual methane emissions to the atmosphere.<ref name="Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-20142">{{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}}</ref> One study reported that the livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane.<ref name="FAO-2006">{{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 }}</ref> A 2013 study estimated that livestock accounted for 44% of human-induced methane and about 15% of human-induced greenhouse gas emissions.<ref name="Tempio-2013">{{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 }}</ref> Many efforts are underway to reduce livestock methane production, such as medical treatments and dietary adjustments,<ref name="Roach-2002">{{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 }}</ref><ref>{{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}}</ref> and to trap the gas to use its combustion energy.<ref name="Silverman-2007">{{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 }}</ref>

==== Seafloor sediments ====

Most of the subseafloor is [[Anoxic waters|anoxic]] because oxygen is removed by [[Aerobic respiration|aerobic]] microorganisms within the first few centimeters of the [[seafloor sediment|sediment]]. Below the oxygen-replete seafloor, methanogens produce methane that is either used by other organisms or becomes trapped in [[Clathrate hydrate|gas hydrates]].<ref name="Dean-2018-2" /> These other organisms that utilize methane for energy are known as [[methanotroph]]s ('methane-eating'), and are the main reason why little methane generated at depth reaches the sea surface.<ref name="Dean-2018-2" /> Consortia of Archaea and Bacteria have been found to oxidize methane via [[anaerobic oxidation of methane]] (AOM); the organisms responsible for this are anaerobic [[methanotroph]]ic Archaea (ANME) and [[Sulfate-reducing microorganism|sulfate-reducing bacteria]] (SRB).<ref name="Knittel-2019">{{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.}}</ref>

===Industrial routes===

[[File:Diagram of sustainable methane fuel production-en.svg|thumb|This diagram shows a method for producing methane sustainably. See: [[electrolysis]], [[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 [[hydrogenation|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, [[Coal assay#Ash|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 fuel|diesel]], or feedstock to other processes.

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

====Laboratory synthesis====

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&nbsp;°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.

==Occurrence==

Methane was discovered and isolated by [[Alessandro Volta]] between 1776 and 1778 when studying [[marsh gas]] from [[Lake Maggiore]]. It 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 organism|anaerobic]] [[Decomposition|decay]] of [[organic matter]] and reworked methane from deep under the Earth's surface. In general, the [[sediment]]s that generate natural gas are buried deeper and at higher temperatures than those that contain [[Petroleum|oil]].

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

==Atmospheric methane and climate change==

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

{{anchor|Methane as a greenhouse gas}}

{{Main|Atmospheric methane}}

[[File:CH4 mm.png|thumb|left|upright=1.2|Methane ({{chem2|CH4}}) measured by the Advanced Global Atmospheric Gases Experiment ([http://agage.mit.edu/ AGAGE]) in the lower atmosphere ([[troposphere]]) at stations around the world. Abundances are given as pollution free monthly mean mole fractions in [[Parts-per notation|parts-per-billion]].]]

Methane is an important [[greenhouse gas]], responsible for around 30% of the rise in global temperatures since the industrial revolution.<ref>{{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}}</ref>

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.<ref name="ar6">{{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/}}</ref> This means that, for example, a [[Fugitive gas emissions|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|left|thumb|Sources of global methane emissions|246x246px]]

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,<ref>{{Cite web |title=Global Methane Budget 2020 |url=https://www.globalcarbonproject.org/methanebudget/ |access-date=2023-09-18 |website=www.globalcarbonproject.org |language=en}}</ref> 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 industry|energy sector]], which includes emissions from coal, oil, natural gas and biofuels.<ref>{{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}}</ref>

[[Keeling Curve|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,<ref name="NASA_2012">{{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}}</ref> but more recent studies associate increasing methane levels as caused by human activity.<ref name="UNEP_2022" />

Global monitoring of atmospheric methane concentrations began in the 1980s.<ref name="UNEP_2022" /> The Earth's atmospheric methane concentration has increased 160% since preindustrial levels in the mid-18th century.<ref name="UNEP_2022" /> In 2013, atmospheric methane accounted for 20% of the total [[radiative forcing]] from all of the long-lived and globally mixed greenhouse gases.<ref>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 }}</ref> Between 2011 and 2019 the annual average increase of methane in the atmosphere was 1866 ppb.<ref name="Technical summary2" /> From 2015 to 2019 sharp rises in levels of atmospheric methane were recorded.<ref>{{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 }}</ref><ref>{{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 }}</ref>

In 2019, the atmospheric methane concentration was higher than at any time in the last 800,000 years. As stated in the [[IPCC Sixth Assessment Report|AR6]] of the [[Intergovernmental Panel on Climate Change|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)".<ref name="Technical summary2" />{{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."}}<ref name="IPCC_2013">{{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}}</ref>

In February 2020, it was reported that [[fugitive emissions]] and [[gas venting]] from the [[fossil fuel industry]] may have been significantly underestimated.<ref name="Hmiel_2020">{{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}}</ref>

<ref name="Harvey_2020">{{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]]}}</ref> The largest annual increase occurred in 2021 with the overwhelming percentage caused by human activity.<ref name="UNEP_2022" />

Climate change can increase atmospheric methane levels by increasing methane production in natural ecosystems, forming a [[climate change feedback]].<ref name="Dean-2018-2" /><ref>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''</ref> Another explanation for the rise in methane emissions could be a slowdown of the chemical reaction that removes methane from the atmosphere.<ref>{{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}}</ref>

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.<ref>{{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}}</ref> 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.<ref>{{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}}</ref> 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".<ref>{{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}}</ref>

===Clathrates===

[[Methane clathrate]]s (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 margin]]s beneath the [[Seabed|ocean floor]] within the [[Gas hydrate stability zone|gas clathrate stability zone]], located at high pressures (1 to 100 MPa; lower end requires lower temperature) and low temperatures (< 15&nbsp;°C; upper end requires higher pressure).<ref name="Bohrmann-2006">{{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=}}</ref> 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.<ref name="Miller-2007">Miller, G. Tyler (2007). ''Sustaining the Earth: An Integrated Approach''. U.S.: Thomson Advantage Books, p. 160. {{ISBN|0534496725}}</ref><ref name="Dean-2018">{{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 }}</ref> The global mass of carbon stored in gas clathrates is still uncertain and has been estimated as high as 12,500 [[Gigaton|Gt]] carbon and as low as 500 Gt carbon.<ref name=":0">{{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}}</ref> The estimate has declined over time with a most recent estimate of ≈1800 Gt carbon.<ref name="Ruppel-2017">{{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}}</ref> 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 [[Mid-ocean ridge|ultraslow spreading ridge]] in the Arctic.<ref name=":1">{{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}}</ref> 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.<ref name="Ruppel-2017" /> [[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]].<ref name="NSF-2010">{{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}}</ref><ref name="Connor-2011">{{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}}</ref><ref name="NSIDC-2012">{{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}}</ref><ref name="UN Environment">{{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}}</ref> Data from 2016 indicate that Arctic permafrost thaws faster than predicted.<ref>{{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}}</ref>

==Public safety and the environment==

[[File:Abatement potential of policy measures, 2021.jpg|thumb|left|200px|An International Energy Agency graphic showing the potential of various emission reduction policies for addressing global methane emissions.]]

Methane "degrades air quality and adversely impacts human health, agricultural yields, and ecosystem productivity".<ref name="Schindell_2012">{{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}}</ref>

Methane is extremely flammable and may form [[explosive]] mixtures with air. Methane gas explosions are responsible for many deadly mining disasters.<ref>{{cite web |author=Dozolme, Philippe |title=Common Mining Accidents |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}}</ref> A methane gas explosion was the cause of the [[Upper Big Branch Mine disaster|Upper Big Branch coal mine disaster]] in [[West Virginia]] on April 5, 2010, killing 29.<ref>{{cite web |author1=Messina, Lawrence |author2=Bluestein, 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}}</ref> [[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.<ref>{{cite journal |last1=OSMAN |first1=Karim |last2=GENIAUT |first2=Baptiste |last3=HERCHIN |first3=Nicolas |last4=BLANCHETIERE |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}}</ref><ref>{{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}}</ref>

The 2015–2016 [[Aliso Canyon gas leak|methane gas leak in Aliso Canyon, California]] was considered to be the worst in terms of its environmental effect in American history.<ref name="LATimes_2016">{{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}}</ref><ref>{{cite web |author=Matt 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 |publisher=BBC}}</ref><ref>{{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 }}</ref> It was also described as more damaging to the environment than [[Deepwater Horizon oil spill|Deepwater Horizon]]'s leak in the Gulf of Mexico.<ref>{{cite news |author=Tim 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}}</ref>

In May 2023 [[The Guardian]] published a report, blaming [[Turkmenistan]] to be 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 tonne]]s of methane in 2022 alone, pumping the [[Carbon dioxide|{{CO2}}]] equivalent of 366 million tonnes into the atmosphere, surpassing the annual {{CO2}} emissions of the [[United Kingdom]].<ref>{{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}}</ref>

Methane is also an [[asphyxiant gas|asphyxiant]] if the oxygen concentration is reduced to below about 16% by displacement, as most people can [[Cabin pressurization#Need for cabin pressurization|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.

== Extraterrestrial methane ==

{{main|Extraterrestrial atmosphere}}

=== Interstellar medium ===

{{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 [[In situ resource utilization|methane production from local materials]] found on [[Mars]]<ref name="zubrin20121215">{{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. }}</ref> or [[Titan (moon)|Titan]]), providing fuel for a return journey.<ref name=aiaa2004/><ref name="nasa20070504">{{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 }}</ref>

=== Mars ===

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 [[Life on Mars|Mars]], it is believed to have come from [[Abiogenic petroleum origin|abiotic]] processes.<ref name="NYT-20121102">{{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 }}</ref><ref>{{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}}</ref>

[[File:PIA19088-MarsCuriosityRover-MethaneSource-20141216.png|thumb|right|[[Atmosphere of Mars#Methane|Methane]] ({{chem2|CH4}}) on Mars{{snd}} potential sources and sinks]]

The [[Curiosity (rover)|''Curiosity'' rover]] has documented seasonal fluctuations of [[Atmosphere of Mars|atmospheric methane]] levels on Mars. These fluctuations peaked at the end of the Martian summer at 0.6 parts per billion.<ref name="NASA-20180607">{{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 }}</ref><ref name="NASA-20180607vid">{{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 }}</ref><ref name="SPC-20180607">{{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 }}</ref><ref name="NYT-20180607">{{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 }}</ref><ref name="SCI-20180607">{{cite journal |last=Voosen |first=Paul |title=NASA rover hits organic pay dirt on Mars |date=June 7, 2018 |journal=[[Science (journal)|Science]] | doi = 10.1126/science.aau3992 |s2cid=115442477 }}</ref><ref name="SCI-20180608a">{{cite journal |last=ten Kate |first=Inge Loes |title=Organic molecules on Mars |date=June 8, 2018 |journal=[[Science (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 }}</ref><ref name="SCI-20180608b">{{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 (journal)|Science]] |volume=360 |issue=6393 |pages=1093–1096 |doi=10.1126/science.aaq0131 |pmid=29880682 |bibcode=2018Sci...360.1093W |doi-access=free }}</ref><ref name="SCI-20180608c">{{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 (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 }}</ref>

Methane has been proposed as a possible [[rocket propellant]] on future [[Human mission to Mars|Mars missions]] due in part to the possibility of synthesizing it on the planet by [[In situ resource utilization#Mars|in situ resource utilization]].<ref>{{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 }}</ref> An adaptation of the [[Sabatier reaction|Sabatier methanation reaction]] may be used with a mixed catalyst bed and a [[Water-gas shift reaction#Reverse water-gas shift|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 soil|Martian subsoil]] and [[carbon dioxide]] in the [[Atmosphere of Mars|Martian atmosphere]].<ref name="zubrin20121215" />

Methane could be produced by a non-biological process called [[serpentinite|serpentinization]]{{efn|name=serpentinization}} involving water, carbon dioxide, and the mineral [[olivine]], which is known to be common on Mars.<ref name="olivine">{{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 }}</ref>

=== Titan ===

[[File:PIA22481-SaturnMoon-Titan-Lakes-20170911.jpg|thumb|200px|{{center|Titan lakes (September 11, 2017)}}]]

Methane has been detected in vast abundance on [[Titan (moon)|Titan]], the largest moon of [[Saturn]], it comprises a significant portion of its [[Atmosphere of Titan|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 Titan|lakes]] of hydrocarbons; the [[Ligeia Mare|second largest]] of which is believed to be almost pure methane in composition.<ref name = "MethaneJPL2016">{{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 }}</ref>

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 on Titan#Hydrocarbons as solvents|life]] existing within Titan's lakes, using methane as a solvent in the place of water for Earth-based life<ref name=methanesolvent>Committee on the Limits of Organic Life in Planetary Systems, Committee on the Origins and Evolution of Life, National Research Council; [http://books.nap.edu/openbook.php?record_id=11919&page=74 The Limits of Organic Life in Planetary Systems]; The National Academies Press, 2007; page 74.</ref> and using hydrogen in the atmosphere to derive energy with [[acetylene]], in much the same way that Earth-based life uses [[glucose]].<ref name=mckay>{{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|author1=McKay, C. P. |author2=Smith, H. D. |bibcode=2005Icar..178..274M|url= https://zenodo.org/record/1259025}}</ref>

==History==

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

Methane was first scientifically identified in November 1776 by [[Italian people|Italian]] physicist [[Alessandro Volta]] in the marshes of [[Lake Maggiore]] straddling [[Italy]] and [[Switzerland]]. Volta was inspired to search for the substance after reading a paper written by [[Benjamin Franklin]] about "flammable air".<ref name="Volta">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.</ref> Volta collected the gas rising from the marsh, and by 1778 had isolated pure methane.<ref name="bookrags">{{cite book |url=http://www.bookrags.com/research/methane-woc/ |title=Methane |publisher=BookRags |access-date=January 26, 2012 |archive-date=March 3, 2016 |archive-url=https://web.archive.org/web/20160303193828/http://www.bookrags.com/research/methane-woc/ |url-status=live }}</ref> He also demonstrated that the gas could be ignited with an electric spark.<ref name=bookrags />

Following the [[Felling mine disasters#1812 disaster|Felling mine disaster]] of 1812 in which 92 men perished, Sir [[Humphry Davy]] established that the feared [[firedamp]] was in fact largely methane.<ref>{{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}}</ref>

The name "methane" was coined in 1866 by the German chemist [[August Wilhelm von Hofmann]].<ref>{{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. 57–58</ref><ref>McBride, 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 }}</ref> The name was derived from [[Methanol#History|methanol]].

==Etymology==

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|methy}} (wine) (related to English "mead") and {{lang|grc|ὕλη}} {{lang|grc-Latn|hyle}} (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]].<ref>{{OEtymD|methane}}</ref>

===Abbreviations===

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.<ref name="methane-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 }}</ref><ref name="epa-ag">{{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 }}</ref> {{chem2|CH4}}-C can also mean the methane-carbon ratio, which is 1.33 by mass.<ref name="mcratio">{{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 }}</ref> 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.<ref name="epa90-20">{{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 }}</ref> Other standard units are also used, such as nanomole (nmol, one billionth of a mole), [[Mole (unit)|mole]] (mol), [[kilogram]], and [[gram]].

==See also==

{{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|Hydrogen Cycle]]

* [[Industrial gas]]

* [[Lake Kivu]] (more general: [[limnic eruption]])

* [[List of straight-chain alkanes]]

* [[Methanation]]

* [[Methane emissions]]

* Methane on Mars:

** [[Atmosphere of Mars#Methane|atmosphere]]

** [[Climate of Mars#Methane presence|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.

== Explanatory notes ==

{{notelist

| notes = {{efn |name=serpentinization |There are many [[serpentinite|''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}} }}}}

== Citations ==

{{Reflist|refs=

<ref name=Rasul>{{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}}</ref>

==Cited sources==

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

==External links==

{{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}}

{{Authority control}}

[[Category:Methane| ]]

[[Category:Anaerobic digestion]]

[[Category:Fuel gas]]

[[Category:Fuels]]

[[Category:Gaseous signaling molecules]]

[[Category:Greenhouse gases]]

[[Category:Industrial gases]]

[[Category:Organic compounds]]

[[Category:Organic compounds with 1 carbon atom]]