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{{Chembox new
| ImageFileL1 = Methane-2D-stereo.svg 
| ImageSizeL1 = 80px
| ImageFileR1 = Methane-3D-balls.png 
| ImageSizeR1 = 80px
| ImageFile2 = Methane-3D-space-filling.svg
| ImageSize2 = 120px
| IUPACName = 
| OtherNames = Marsh gas, [[firedamp]] 
| Section1 = {{Chembox Identifiers
|   CASNo = 74-82-8
|   PubChem = 
|   ChemSpiderID = 291
|   SMILES = C
|   InChI=1/CH4/h1H4
  }}
| Section2 = {{Chembox Properties
|   Formula = CH<sub>4</sub>
|   MolarMass = 16.0425 g/mol
|   Appearance = Colorless gas
|   Density = 0.717 kg/m<sup>3</sup>, gas
|   MeltingPtC = -182.5
|   BoilingPtC = -161.6
|   Solubility = 3.5 mg/100 mL (17 °C)
  }}
| Section3 = {{Chembox Hazards
|   MainHazards = Highly flammable ('''F+''')
|   NFPA-H = 1 | NFPA-F = 4 | NFPA-R = 0
|   RPhrases = {{R12}}
|   SPhrases = {{(S2)}}, {{S9}}, {{S16}}, {{S33}}
|   FlashPt = -188 °C
|   Autoignition = 
  }}
| Section8 = {{Chembox Related
| OtherFunctn = [[Ethane]], [[propane]]
| Function = [[Alkane]]s
| OtherCpds = [[Methanol]], [[chloromethane]], [[formic acid]], [[formaldehyde]], [[silane]]
  }}
}}
'''Methane''' is a [[chemical compound]] with the molecular formula {{chem|CH|4}}. It is the simplest [[alkane]], and the principal component of [[natural gas]]. Methane's bond angles are 109.5 degrees. [[Combustion|Burning]] methane in the presence of [[oxygen]] produces [[carbon dioxide]] and water.
The relative abundance of methane and its clean burning process makes it a very attractive [[fuel]]. However, because it is a gas at [[Standard temperature and pressure|normal temperature and pressure]], methane is difficult to transport from its source. In its [[natural gas]] form, it is generally transported in bulk by [[Pipeline transport|pipeline]] or [[LNG carrier]]s; few countries still transport it by truck.

Methane is a relatively potent [[greenhouse gas]] with a high [[global warming potential]] of 72 (averaged over 20 years) or 25 (averaged over 100 years).<ref>[http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf IPCC Fourth Assessment Report]</ref> Methane in the atmosphere is eventually oxidized, producing carbon dioxide and water. As a result, methane in the atmosphere has a [[half life]] of seven years (if no methane were added, then every seven years, the amount of methane would halve). 

The abundance of methane in the Earth's atmosphere in 1998 was 1745 parts per billion, up from 700 ppb in 1750. In the same time period, CO<sub>2</sub> increased from 278 to 365 parts per million. The [[radiative forcing]] effect due to this increase in methane abundance is about one-third of that of the CO<sub>2</sub> increase.<ref>{{cite web|url=http://www.grida.no/climate/ipcc_tar/wg1/221.htm|title=Radiative Forces of Climate Change|work=Climate Change 2001: The Scientific Basis|publisher=IPCC|accessdate=2008-05-26}}</ref> In addition, there is a large, but unknown, amount of methane in [[methane clathrate]]s in the ocean floors. The Earth's [[crust(geology)| crust]] contains huge amounts of methane. Large amounts of methane are produced [[anaerobic]]ally by [[methanogenesis]]. Other sources include [[mud volcano]]es which are connected with deep geological faults.

==Properties==

Methane is the major component of [[natural gas]], about 87% by volume. At [[room temperature]] and [[standard pressure]], methane is a colorless, odorless gas; the smell characteristic of natural gas is an artificial safety measure caused by the addition of an [[odorant]], often [[methanethiol]] or [[ethanethiol]]. Methane has a boiling point of −161 °[[Celsius|C]] at a pressure of one [[Atmosphere (unit)|atmosphere]]. As a gas it is [[flammable]] only over a narrow range of concentrations (5–15%) in air. Liquid methane does not burn unless subjected to high pressure (normally 4–5 atmospheres).

===Potential health effects===
Methane is not toxic; however, it is highly flammable and may form [[explosive]] mixtures with air. Methane is violently reactive with [[oxidizer]]s, [[halogen]]s, and some halogen-containing compounds. Methane is also an [[asphyxiant gas|asphyxiant]] and may displace [[oxygen]] in an enclosed space. [[Asphyxia]] may result if the oxygen concentration is reduced to below 19.5% by displacement {{Fact|date=July 2008}}. The concentrations at which flammable or explosive mixtures form are much lower than the concentration at which asphyxiation risk is significant. When structures are built on or near [[landfill]]s, methane off-gas can penetrate the buildings' interiors and expose occupants to significant levels of methane. Some buildings have specially engineered recovery systems below their basements to actively capture such fugitive off-gas and vent it away from the building. An example of this type of system is in the [[Dakin Building]], [[Brisbane, California]].

===Reactions of methane===
Main reactions with methane are: [[combustion]], [[steam reforming]] to [[syngas]], and [[halogenation]]. In general, methane reactions are hard to control. Partial oxidation to [[methanol]], for example, is difficult to achieve; the reaction typically progresses all the way to [[carbon dioxide]] and [[water]].

====Combustion====
In the [[combustion]] of methane, several steps are involved:

Methane is believed to form a [[formaldehyde]] (HCHO or {{chem|H|2|CO}}). The formaldehyde gives a formyl [[Radical (chemistry)|radical]] (HCO), which then forms [[carbon monoxide]] (CO). The process is called oxidative [[pyrolysis]]: 

<div style='text-align: center;'>
{{chem|CH|4|&nbsp;+ O|2|&nbsp;→ CO + H|2|&nbsp;+ H|2|O}}
</div>

Following oxidative pyrolysis, the {{chem|H|2}} oxidizes, forming {{chem|H|2|O}}, replenishing the active species,{{huh}} and releasing [[heat]]. This occurs very quickly, usually in significantly less than a [[millisecond]].

<div style='text-align: center;'>
{{chem|2H|2|&nbsp;+ O|2|&nbsp;→2H|2|O}}
</div>

Finally, the CO [[oxidize]]s, forming {{chem|CO|2}} and releasing more heat. This process is generally slower than the other chemical steps, and typically requires a few to several milliseconds to occur.

<div style='text-align: center;'>
{{chem|2CO + O|2|&nbsp;→2CO|2}}
</div>

The result of the above is the following total equation:

<div style='text-align: center;'>
CH<sub>4</sub>(g) + 2O<sub>2</sub>(g) → CO<sub>2</sub>(g) + 2H<sub>2</sub>O(l) + 890 [[kilo-|k]][[joule|J]]/[[Mole (unit)|mol]]<ref>SCHAUM'S OUTLINE SERIES, ORGANIC CHEMISTRY</ref>
</div>
where bracketed "g" stands for gaseous form and bracketed "l" stands for liquid form.

====Hydrogen activation====
The strength of the [[carbon]]-[[hydrogen]] [[covalent bond]] in methane is among the strongest in all hydrocarbons, and thus its use as a chemical feedstock is limited. Despite the high activation barrier for breaking the C–H bond, {{chem|CH|4}} is still the principal starting material for manufacture of [[hydrogen]] in [[steam reforming]]. The search for [[catalyst]]s which can facilitate C–H bond activation in methane and other low [[alkane]]s is an area of research with considerable industrial significance.

====Reactions with halogens====
Methane reacts with all halogens given appropriate conditions, as follows:

<div style='text-align: center;'>
{{chem|CH|4|&nbsp;+ X|2|&nbsp;→ CH|3|X + HX}}
</div>

where X is a [[halogen]]: [[fluorine]] (F), [[chlorine]] (Cl), [[bromine]] (Br), or [[iodine]] (I). This mechanism for this process is called [[free radical halogenation]].
When X is Cl, this mechanism has the following form:
* If used isomolecular (equal molecule analogy) quantities in  CH<sub>2</sub>X<sub>2</sub>, CHX<sub>3</sub>, even CX<sub>4</sub> also produses. Using a large overquantitity of CH<sub>4</sub> reduces the production of CH<sub>2</sub>X<sub>2</sub>, CHX<sub>3</sub>, X<sub>4</sub> and more clean CH<sub>3</sub>X produces.

1. Radical generation: 

<div style='text-align: center;'>
<math>Cl_2 \xrightarrow[\triangle]{UV} 2Cl^. - 239 kJ </math>
</div>
* The needed energy comes from UV radiation or heating,

2. Radical exchanges:

<div style='text-align: center;'>
<math>CH_4 + Cl^.\xrightarrow{} CH_3^. + HCl + 14 kJ  </math> <br />
<math>CH_3^. + Cl_2 \xrightarrow{} CH_3Cl + Cl^. + 100 kJ </math>
</div>

3. Radiacal extermination:

<div style='text-align: center;'>
<math> 2Cl^. \xrightarrow{} Cl_2 + 239 kJ </math><br />
<math> CH_3^. + Cl^. \xrightarrow{} CH_3Cl + 339 kJ </math><br />
<math> 2CH_3^. \xrightarrow{} CH_3CH_3 + 347 kJ </math>
</div>

== Uses ==
=== Fuel ===

:''For more on the use of methane as a fuel, see: [[natural gas]]''

Methane is important for [[electrical generation]] by burning it as a fuel in a [[gas turbine]] or steam [[boiler]]. Compared to other [[fossil fuel|hydrocarbon fuel]]s, burning methane produces less [[carbon dioxide]] for each unit of heat released. At about 891 kJ/mol, methane's combustion heat is lower than any other hydrocarbon; but a ratio with the molecular mass (16.0 g/mol) divided by the heat of combustion (891 kJ/mol) shows that methane, being the simplest hydrocarbon, produces more heat per mass unit than other complex hydrocarbons. In many cities, methane is piped into homes for domestic [[heating]] and cooking purposes. In this context it is usually known as [[natural gas]], and is considered to have an energy content of 39 [[megajoule]]s per cubic meter, or 1,000 [[BTU]] per [[standard cubic foot]].

Methane in the form of [[compressed natural gas]] is used as a [[vehicle fuel]], and is claimed to be more environmentally friendly than  fossil fuels such as gasoline/petrol and diesel.{{Who|date=July 2008}}

Research is being conducted by [[NASA]] on methane's potential as a [[rocket fuel]]. One advantage of methane is that it is abundant in many parts of the solar system and it could potentially be harvested ''in situ'', providing fuel for a return journey. <ref>http://science.nasa.gov/headlines/y2007/04may_methaneblast.htm?list123532</ref>

=== Industrial uses ===

Methane is used in industrial chemical processes and 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 pipeline]]s distribute large amounts of [[natural gas]], of which methane is the principal component.

In the chemical industry, methane is the feedstock of choice for the production of [[hydrogen]], [[methanol]], [[acetic acid]], and [[acetic anhydride]].  When used to produce any of these chemicals, methane is first converted to [[synthesis gas]], a mixture of [[carbon monoxide]] and [[hydrogen]], by [[steam reforming]].  In this process, methane and [[steam]] react on a [[nickel]] catalyst at high temperatures (700–1100 °C).

<div style='text-align: center;'>
<math>CH_4 + H_2O \xrightarrow[700-1100^oC]{Ni} CO + 3H_2  </math>
</div>

The ratio of carbon monoxide to hydrogen in synthesis gas can then be adjusted via the [[water gas shift reaction]] to the appropriate value for the intended purpose.

<div style='text-align: center;'>
{{chem|CO + H|2|O → CO|2| + H|2}}
</div>

Less significant methane-derived chemicals include [[acetylene]], prepared by passing methane through an [[electric arc]], and the chloromethanes ([[chloromethane]], [[dichloromethane]], [[chloroform]], and [[carbon tetrachloride]]), produced by reacting methane with [[chlorine]] gas.  However, the use of these chemicals is declining, acetylene as it is replaced by less costly substitutes, and the chloromethanes due to health and environmental concerns.

== Sources of methane ==
===Natural gas fields===

The major source of methane is extraction from geological deposits known as [[natural gas fields]]. It is associated with other [[hydrocarbon]] fuels and sometimes accompanied by [[helium]] and [[nitrogen]]. The gas at shallow levels (low pressure) is formed by [[anaerobic organism|anaerobic]] [[decay]] of [[organic matter]] and reworked methane from deep under the Earth's surface. In general, sediments buried deeper and at higher temperatures than those which give [[Petroleum|oil]] generate natural gas.  Methane is also produced in considerable quantities from the decaying organic wastes of [[solid waste]] [[landfill]]s.

===Alternative sources===

Apart from gas fields an alternative method of obtaining methane is via [[biogas]] generated by the [[fermentation (biochemistry)|fermentation]] of organic matter including [[manure]], wastewater sludge, municipal solid waste (including landfills), or any other biodegradable feedstock, under anaerobic conditions.  Methane hydrates/clathrates (icelike combinations of methane and water on the sea floor, found in vast quantities) are a potential future source of methane.  Cattle belch methane accounts for 16% of the world's annual methane emissions to the atmosphere. <ref> Miller, G. Tyler. Sustaining the Earth: An Integrated Approach. U.S.A.: Thomson Advantage Books, 2007. 160.</ref> The livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane".<ref>{{cite web |url=http://www.virtualcentre.org/en/library/key_pub/longshad/A0701E00.htm
|title=Livestock’s Long Shadow–Environmental Issues and Options|accessdate=2007-01-04}}</ref>  However animals "that put their energies into making gas are less efficient at producing milk and meat".  Early research has found a number of medical treatments and dietary adjustments that help limit the production of methane in [[ruminants]].<ref>[http://news.nationalgeographic.com/news/2005/08/0816_050816_cowpollution_2.html California Cows Fail Latest Emissions Test<!-- Bot generated title -->]</ref> <ref>[http://news.nationalgeographic.com/news/2002/05/0509_020509_belch.html New Zealand Tries to Cap Gaseous Sheep Burps<!-- Bot generated title -->]</ref>
<ref>[http://www.alternet.org/story/72339/ Research on use of bacteria from the stomach lining of kangaroos (who don't emit methane) to reduce methane in cattle<!-- Bot generated title -->]</ref>

Industrially, methane can be created from common atmospheric gases and hydrogen (produced, for example, by [[electrolysis]]) through chemical reactions such as the [[Sabatier process]], [[Fischer-Tropsch process]]. [[Coal bed methane extraction]] is a method for extracting methane from a [[coal]] deposit, while [[enhanced coal bed methane recovery]] is a method of recovering methane from an unminable coal seam.

A recent scientific experiment has also yielded results pointing to one species of plant<ref>[http://environment.newscientist.com/article/mg19626322.900-plants-do-emit-methane-after-all.html Plants do emit methane after all - earth - 02 December 2007 - New Scientist Environment<!-- Bot generated title -->]</ref> producing trace methane.<ref>Methane emissions from terrestrial plants under aerobic conditions Nature, January 12, 2006</ref>.

== Methane in Earth's atmosphere ==<!-- This section is linked from [[Clathrate hydrate]] -->
[[Image:Ch4rug multicolor.png|thumb|250px|Methane concentrations graph]]
[[Image:AtmosphericMethane.png|thumb|250px|Computer models showing the amount of methane (parts per million by volume) at the surface (top) and in the stratosphere (bottom).]]

Early in the Earth's history—about 3.5 billion years ago—there was 1,000 times as much methane in the atmosphere as there is now. The earliest methane was released into the atmosphere by volcanic activity. During this time, Earth's earliest life appeared. These first, ancient bacteria added to the methane concentration by converting hydrogen and carbon dioxide into methane and water. Oxygen did not become a major part of the atmosphere until photosynthetic organisms evolved later in Earth's history. With no oxygen, methane stayed in the atmosphere longer and at higher concentrations than it does today.

In present times, due to the increase in oxygen, the amount of methane has decreased. The average mole concentration of methane at the Earth's surface in 1998 was 1,745 [[ppb]].<ref name="Trace Gases">{{cite web|url=http://www.grida.no/climate/ipcc_tar/wg1/134.htm#4211|title=Trace Gases: Current Observations, Trends, and Budgets|work=Climate Change 2001|publisher=United Nations Environment Programme}}</ref> Its concentration is higher in the northern hemisphere as most sources (both natural and human) are larger. The concentrations vary seasonally with a minimum in the late summer mainly due to removal by the [[hydroxyl radical]].

Methane is created near the surface, and it is carried into the [[stratosphere]] by rising air in the [[tropics]]. Uncontrolled build-up of methane in Earth's atmosphere is naturally checked—although human influence can upset this natural regulation—by methane's reaction with [[hydroxyl radical]]s formed from [[singlet oxygen]] atoms and with water vapor.

===Methane as a greenhouse gas===

Methane in the Earth's atmosphere is an important greenhouse gas with a global warming potential of 25 over a 100-year period. This means that a methane emission will have 25 times the impact on temperature of a carbon dioxide emission of the same mass over the following 100 years. Methane has a large effect for a brief period (a net lifetime of 8.4 years in the atmosphere), whereas carbon dioxide has a small effect for a long period (over 100 years). Because of this difference in effect and time period, the global warming potential of methane over a 20 year time period is 72. The Earth's methane concentration has increased by about 150% since 1750, and it accounts for 20% of the total [[radiative forcing]] from all of the long-lived and globally mixed greenhouse gases.<ref name="Technical summary">{{cite web|url=http://www.grida.no/climate/ipcc_tar/wg1/017.htm|title=Technical summary|work=Climate Change 2001|publisher=United Nations Environment Programme}}</ref> Usally, excess methane from landfills and other natural producers of methane are burned so CO<sub>2</sub> is released into the atmosphere instead of methane because methane is such a more effective greenhouse gas.

===Emissions of methane===

Houweling et al. (1999) give the following values for methane emissions (Tg/a=teragrams per year):<ref name="Trace Gases"/>

[[Image:Methane-global-average-2006.jpg|thumb|right|250px|Global average methane concentrations from measurement (NOAA)]]

{|  style="text-align: right;" border="1" cellspacing="0" class="wikitable"
!rowspan=2|Origin
!colspan=3|{{chem|CH|4}} Emission
|-
!Mass (Tg/[[annum|a]])
!Type (%/a)
!Total (%/a)
|-
!colspan=4|Natural Emissions
|- 
|{{rh}}|[[Wetland]]s (incl. Rice agriculture)
| 225
| 83
| 37
|- 
|{{rh}}|[[Termite]]s
| 20
| 7
| 3
|- 
|{{rh}}|[[Ocean]]
| 15
| 6
| 3
|- 
|{{rh}}|[[Hydrate]]s
| 10
| 4
| 2
|-
|{{rh}}|Natural Total
| 270
| 100
| 45
|-
!colspan=4|[[Anthropogenic|Anthropogenic Emissions]]
|-
|{{rh}}|Energy
| 110
| 33
| 18
|-
|{{rh}}|[[Landfill]]s
| 40
| 12
| 7
|-
|{{rh}}|[[Ruminant]]s (Livestock)
| 115
| 35
| 19
|-
|{{rh}}|Waste treatment
| 25
| 8
| 4
|-
|{{rh}}|Biomass burning
| 40
| 12
| 7
|-
|{{rh}}|Anthropogenic Total
| 330
| 100
| 55
|-
!colspan=4|Sinks
|- 
|{{rh}}|[[Soil]]s
| -30
| -5
| -5
|- 
|{{rh}}|[[Troposphere|Tropospheric]] [[Hydroxyl|OH]]
| -510
| -88
| -85
|- 
|{{rh}}|[[Stratosphere|Stratospheric]] loss
| -40
| -7
| -7
|- 
|{{rh}}|Sink Total
| -580
| -100
| -97
|-
!colspan=4|Emissions + Sinks
|-
|{{rh}}|Imbalance (trend)
| +20
| ~2.78 Tg/ppb
| +7.19 ppb/a
|}
Slightly over half of the total emission is due to human activity.<ref name="Technical summary"/>

Living plants (e.g. forests) have recently been identified as a potentially important source of methane. A 2006 paper calculated emissions of 62–236 Tg [[annum|a]]<sup>-1</sup>, and "this newly identified source may have important implications".<ref>{{cite web|url=http://www.nature.com/nature/journal/v439/n7073/abs/nature04420.html|title=Methane emissions from terrestrial plants under aerobic conditions|publisher=Nature|accessdate=2006-09-07|date=2006-01-12}}</ref><ref>{{cite web|url=http://news.bbc.co.uk/2/hi/science/nature/4604332.stm|title=Plants revealed as methane source|publisher=BBC|accessdate=2006-09-07|date=2006-01-11}}</ref> However the authors stress "our findings are preliminary with regard to the methane emission strength".<ref>{{cite web|url=http://www.eurekalert.org/pub_releases/2006-01/m-gw-011806.php|title=Global warming - the blame is not with the plants|publisher=eurekalert.org|accessdate=2006-09-06|date=2006-01-18}}</ref> These findings have been called into question in a 2007 paper which found ''"there is no evidence for substantial aerobic methane emission by terrestrial plants, maximally 0.3% of the previously published values"''.<ref>{{cite journal|last=Duek|first=Tom A.|coauthors=Ries de Visser, Hendrik Poorter, Stefan Persijn, Antonie Gorissen, Willem de Visser, Ad Schapendonk, Jan Verhagen, Jan Snel, Frans J. M. Harren, Anthony K. Y. Ngai, Francel Verstappen, Harro Bouwmeester, Laurentius A. C. J. Voesenek, Adrie van der Werf|url=http://www.blackwell-synergy.com/doi/abs/10.1111/j.1469-8137.2007.02103.x|title=No evidence for substantial aerobic methane emission by terrestrial plants: a <sup>13</sup>C-labelling approach.|journal =New Phytologist  | publisher =Blackwell  | doi=10.1111/j.1469-8137.2007.02103.x|accessdate=2007-04-23|date=2007-03-30 | volume = 175 | pages = 29}}</ref>

Long term atmospheric measurements of methane by [[NOAA]] show that the build up of methane has slowed dramatically over the last decade, after nearly tripling since pre-industrial times <ref>{{cite web|url=http://www.noaanews.noaa.gov/stories2006/s2709.htm|title=SCIENTISTS PINPOINT CAUSE OF SLOWING METHANE EMISSIONS| work =NOAA news Online|accessdate=2007-05-23}}</ref>. It is thought that this reduction is due to reduced industrial emissions and drought in wetland areas.

Very recent data now suggests that methane concentrations may be rising again <ref>{{cite web|url=http://www.esrl.noaa.gov/media/2008/aggi.html|title=Annual Greenhouse Gas Index (AGGI) Indicates Sharp Rise in Carbon Dioxide and Methane in 2007=NOAA news Online|accessdate=2008-06-16}}</ref>.

===Removal processes ===

The major removal mechanism of methane from the atmosphere involves [[Radical (chemistry)|radical chemistry]] ; it reacts with the [[hydroxyl radical]] ('''·'''OH), initially formed from water vapor broken down by oxygen atoms that come from the cleavage of [[ozone]] by [[ultraviolet]] radiation:

: {{chem|CH|4|&nbsp;+ '''·'''OH → '''·'''CH|3|&nbsp;+ H|2|O}}

This reaction in the [[troposphere]] gives a methane lifetime of 9.6 years. Two more minor sinks are soil sinks (160 year lifetime) and stratospheric loss by reaction with '''·'''OH, '''·'''Cl and '''·'''O<sup>1</sup>D in the stratosphere (120 year lifetime), giving a net lifetime of 8.4 years.<ref name="Trace Gases"/> Oxidation of methane is the main source of water vapor in the upper stratosphere (beginning at pressure levels around 10 kPa).

The methyl radical formed in the above reaction will, during normal daytime conditions in the troposphere, usually react with another hydroxyl radical to form [[formaldehyde]].  Note that this is not strictly oxidative [[pyrolysis]] as described previously. Formaldehyde can react again with a hydroxyl radical to form [[carbon dioxide]] and more water vapor. Note that sidechains in these reatcions may interact with [[nitrogen]] compounds that will likely produce [[ozone]], thus supplanting radicals required in the initial reaction. <ref>{{cite web|url=http://www.atmosp.physics.utoronto.ca/people/loic/chemistry.html|title=Methane and Carbon Monoxide in the Troposphere|accessdate=2008-07-18}}</ref>

===Sudden release from methane clathrates===
{{Refimprovesect|date=July 2008}}

At high pressures, such as are found on the bottom of the ocean, methane forms a solid [[clathrate]] with water, known as [[methane clathrate|methane hydrate]]. An unknown, but possibly very large quantity of methane is trapped in this form in ocean sediments.  The sudden release of large volumes of methane from such sediments into the atmosphere has been suggested as a possible cause for rapid [[global warming]] events in the Earth's distant past, such as the [[Paleocene–Eocene Thermal Maximum]] of 55 million years ago.

Theories suggest that should global warming cause them to heat up sufficiently, all of this methane could again be suddenly released into the atmosphere. Since methane is twenty-five times stronger (for a given weight, averaged over 100 years) than {{chem|CO|2}} as a greenhouse gas; this would immensely magnify the greenhouse effect, heating Earth to unprecedented levels (see [[Clathrate gun hypothesis]]).

===Release of methane from bogs===
Although less dramatic than release from clathrates, but already happening, is an increase in the release of methane from bogs as [[permafrost]] melts. Although records of permafrost are limited, recent years (1999 to 2007) have seen record thawing of permafrost in [[Alaska]] and [[Siberia]]. 

Recent measurements in Siberia show that the methane released is five times greater than previously estimated <ref>{{cite web|url=http://news.bbc.co.uk/2/hi/science/nature/5321046.stm|title=Methane bubbles climate trouble|publisher=BBC|accessdate=2006-09-07|date=2006-09-07}}</ref>.

==Extraterrestrial methane==
Methane has been detected or is believed to exist in several locations of the [[solar system]].  It is believed to have been created by [[Abiotic components|abiotic]] processes, with the possible exception of [[Life on Mars|Mars]].

* [[Moon]] - traces are present in the thin atmosphere<ref>{{cite journal | last = Stern | first = S.A. | title = The Lunar atmosphere: History, status, current problems, and context | journal = Rev. Geophys. | volume = 37 | date = 1999 | pages = 453&ndash;491 | doi = 10.1029/1999RG900005}}</ref>
* [[Mars]] - the atmosphere contains 10 ppb methane
* [[Jupiter (planet)|Jupiter]] - the atmosphere contains about 0.3% methane
* [[Saturn (planet)|Saturn]] - the atmosphere contains about 0.4% methane
** [[Iapetus (moon)|Iapetus]]
** [[Titan (moon)|Titan]] — the atmosphere contains 1.6% methane<ref name=Niemann>
{{cite journal | title= The abundances of constituents of Titan’s atmosphere from the GCMS instrument on the Huygens probe |author= H. B. Niemann, et al. |journal= [[Nature]] |volume=438 |pages=779–784 |year=2005 |doi=10.1038/nature04122 }}</ref>
** [[Enceladus (moon)|Enceladus]] - the atmosphere contains 1.7% methane<ref name=Waite>Waite, J. H.; ''et al.''; (2006); [http://www.sciencemag.org/cgi/content/abstract/311/5766/1419 ''Cassini Ion and Neutral Mass Spectrometer: Enceladus Plume Composition and Structure''], Science, Vol. 311, No. 5766, pp. 1419–1422</ref>
* [[Uranus (planet)|Uranus]] - the atmosphere contains 2.3% methane 
** [[Ariel (moon)|Ariel]] - methane is believed to be a constituent of Ariel's surface ice
** [[Miranda (moon)|Miranda]]
** [[Oberon (moon)|Oberon]] - about 20% of Oberon's surface ice is composed of methane-related carbon/nitrogen compounds
** [[Titania (moon)|Titania]] - about 20% of Titania's surface ice is composed of methane-related organic compounds
** [[Umbriel (moon)|Umbriel]] - methane is a constituent of Umbriel's surface ice
* [[Neptune (planet)|Neptune]] -  the atmosphere contains 1.6% methane
** [[Triton (moon)|Triton]] - Triton has a tenuous nitrogen atmosphere with small amounts of methane near the surface.<ref name=nature2>{{cite journal
 | title = Ultraviolet Spectrometer Observations of Neptune and Triton
 | author = A L Broadfoot, S K Bertaux, J E Dessler et al.
 | url = http://adsabs.harvard.edu/abs/1989Sci...246.1459B
 | date = [[December 15]] [[1989]]
 | journal = Science
 | volume = 246
 | pages = 1459–1466
 | accessdate = 2008-01-15
 | doi = 10.1126/science.246.4936.1459
 | pmid = 17756000
}}</ref><ref name=grand>{{cite book
 | title = The Grand Tour: A Traveler's Guide to the Solar System
 | author = Ron Miller
 | authorlink = Ron Miller (artist and author)
 | coauthors = William K. Hartmann
 | year = 2005
 | month = May
 | pages = 172&ndash;73
 | publisher = Workman Publishing
 | location = Thailand
 | edition = 3rd
 | isbn = 0-7611-3547-2
}}</ref>
* [[Pluto]] - [[spectroscopic]] analysis of Pluto's surface reveals it to contain traces of methane<ref>{{cite journal|title = Surface Ices and the Atmospheric Composition of Pluto |author = Tobias C. Owen, Ted L. Roush et al.| journal = Science |year=1993 | month = 6 August | volume = 261 | issue = 5122 | pages = 745–748 |doi =  10.1126/science.261.5122.745 |url=http://www.sciencemag.org/cgi/content/abstract/261/5122/745 |accessdate=2007-03-29|pmid = 17757212}}</ref><ref name=Solstation>{{cite web|title=Pluto|work=SolStation|url=http://www.solstation.com/stars/pluto.htm|year=2006|accessdate=2007-03-28}}</ref>
**[[Charon (moon)|Charon]] - methane is believed to be present on Charon, but it is not completely confirmed<ref>{{cite journal |author=B. Sicardy et al |title=''Charon’s size and an upper limit on its atmosphere from a stellar occultation'' |journal=Nature |year=2006 |volume=439 |pages=52 |url=http://www.nature.com/nature/journal/v439/n7072/abs/nature04351.html | doi = 10.1038/nature04351 <!--Retrieved from CrossRef by DOI bot-->}}</ref>
* [[Eris (dwarf planet)|Eris]] - infrared light from the object revealed the presence of methane ice
* [[Comet Halley]]
* [[Comet Hyakutake]] - terrestrial observations found [[ethane]] and methane in the comet<ref name="science">{{cite journal | author=Mumma, M.J. | coauthors = Disanti, M.A., dello Russo, N., Fomenkova, M., Magee-Sauer, K., Kaminski, C.D., and D.X. Xie | title=Detection of Abundant Ethane and Methane, Along with Carbon Monoxide and Water, in Comet C/1996 B2 Hyakutake: Evidence for Interstellar Origin | journal=Science | year=1996 | volume=272 | pages=1310 | url={{ADS|1996Sci...272.1310M}}  | doi = 10.1126/science.272.5266.1310 <!--Retrieved from CrossRef by DOI bot-->}}</ref>
* [[Extrasolar planet]] [[HD 189733b]] - This is the first detection of an organic compound on planets outside the solar system. It is unknown how it originated, when the high temperature (700°C) favors the formation of [[carbon monoxide]] instead. <ref>{{cite web|url=http://space.newscientist.com/article/dn13303-organic-molecules-found-on-alien-world-for-first-time.html|title=Organic molecules found on alien world for first time|accessdate=2008-02-12|author=Stephen Battersby|date=2008-02-11}}</ref>
* [[Interstellar cloud]]s<ref>{{cite journal | author=J. H. Lacy, J. S. Carr, N. J. Evans, II, F. Baas, J. M. Achtermann, J. F. Arens | title=Discovery of interstellar methane - Observations of gaseous and solid CH4 absorption toward young stars in molecular clouds | journal=Astrophysical Journal | year=1991 | volume=376 | pages=556–560 | url=http://adsabs.harvard.edu/abs/1991ApJ...376..556L  | doi = 10.1086/170304 <!--Retrieved from CrossRef by DOI bot-->}}</ref>

==See also== 
{{Portalpar|Sustainable development|Sustainable development.svg}}
<div style="-moz-column-count:3; column-count:3;">
*[[2007 Zasyadko mine disaster]]
*[[Abiogenic petroleum origin]]
*[[Anaerobic digestion]]
*[[Anaerobic respiration]]
*[[Biogas]]
*[[Greenhouse gas]]
*[[Halomethane]], halogenated methane derivatives.
*[[List of alkanes]]
*[[Methanation]]
*[[Methane clathrate]], form of water ice which contains methane.
*[[Methanogen]], [[archaea]] that produce methane as a metabolic by-product.
*[[Methanogenesis]], the formation of methane by [[microbes]].
*[[Methanotroph]], [[bacteria]] that are able to grow using methane as their only source of carbon and energy.
*[[Methyl group]], a functional group similar to methane.
*[[Organic gas]]
*[[Thomas Gold]]
</div>

==References==
{{reflist|2}}

==External links==
{{Commons|Methane}}
{{Wiktionarypar|methane}}
*Gavin Schmidt, [http://www.giss.nasa.gov/research/features/methane/ Methane: A Scientific Journey from Obscurity to Climate Super-Stardom], [[Goddard Institute for Space Studies|NASA Goddard]], September 2004
*[http://www.gasresources.net Methane thermodynamics]
*[http://www.newmediaexplorer.org/sepp/2005/02/01/global_warming_methane_could_be_far_worse_than_carbon_dioxide.htm  Methane in tundra and oceans to be released in atmosphere]
*[http://www-cms.llnl.gov/s-t/cheetah_methane_str.html Inorganic Methane]
*[http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc02/icsc0291.htm International Chemical Safety Card 0291]
*[http://marine.usgs.gov/fact-sheets/gas-hydrates/title.html Methane Hydrates]
*[http://www.compchemwiki.org/index.php?title=Methane Computational Chemistry Wiki]
*[http://ptcl.chem.ox.ac.uk/MSDS/ME/methane.html Safety data for methane]
*[http://twt.mpei.ac.ru/MAS/Worksheets/HEDH/5-5-14-03-16/Tab-5-5-14-03-METHANE-viscosity.mcd Dynamic Viscosity of Methane]
*[http://twt.mpei.ac.ru/MAS/Worksheets/HEDH/5-5-14-03-16/Tab-5-5-14-03-METHANE-thermal.mcd Thermal Conductivity of Methane]
* [http://www.gns.cri.nz/news/release/20071122methane.html METHANE-EATING BUG HOLDS PROMISE FOR CUTTING GREENHOUSE GAS]. Media Release, GNS Science, New Zealand]
* [http://pire-ecci.ucsb.edu/summerschool/papers/Catalysis%20Today.pdf Catalytic conversion of methane to more useful chemicals and fuels]

{{alkanes}}

[[Category:Methane| ]]
[[Category:Anaerobic digestion]]
[[Category:Greenhouse gases]]
[[Category:Fuels]]
[[Category:Fuel gas]]

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