Methane emissions

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

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

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

About one-third (33%) of anthropogenic emissions are from gas release during the extraction and delivery of fossil fuels; mostly due to gas venting and gas leaks. Animal agriculture is a similarly large source (30%); primarily because of enteric fermentation by ruminant livestock such as cattle and sheep. Human consumer waste flows, especially those passing through landfills and wastewater treatment, have grown to become a third major category (18%). Plant agriculture, including both food and biomass production, constitutes a fourth group (15%), with rice production being the largest single contributor.[1][6]

The world's wetlands contribute about three-quarters (75%) of the enduring natural sources of methane.[3][4] Seepages from near-surface fossil-fuel and clathrate hydrate deposits (unrelated to direct human action), volcanic releases, wildfires, and termite emissions account for much of the remainder.[6] Contributions from the surviving wild populations of ruminant mammals are vastly overwhelmed by those of cattle, humans, and other livestock animals.[7]

Atmospheric concentration and warming influence
Globally averaged atmospheric CH4 and its annual growth rate GATM[8]

The atmospheric methane (CH4) concentration is increasing and has exceeded 1860 parts per billion as of year 2019, equal to two-and-a-half times the pre-industrial level.[9] The methane itself enables a direct radiative forcing that is second only to that of carbon dioxide (CO2).[10] Due to interactions with oxygen compounds stimulated by sunlight, CH4 can also increase the atmospheric presence of shorter-lived ozone and water vapour, which are also potent warming gases that amplify methane's near-term warming influence in a mechanism that atmospheric researchers distinguish as indirect radiative forcing.[11] When such interactions occur, longer-lived and less-potent CO2 is also produced. Including both the direct and indirect forcings, the increase in atmospheric methane is responsible for about one-third of near-term climate warming. [1][2]

To compare the warming to that from carbon dioxide over a given time period, methane in the atmospheric has an estimated 20-year global warming potential (GWP) of 85, meaning that a ton of CH4 emitted into the atmosphere creates approximately 85 times the atmospheric warming as a ton of CO2 over a period of 20 years.[12] On a 100-year timescale, the GWP is in the range of 28-34. Though methane causes far more heat to be trapped than the same mass of carbon dioxide, less than half of the emitted CH4 remains in the atmosphere after a decade. On average, carbon dioxide warms for a much longer time period assuming no change in rates of carbon sequestration.[13] [12]

List of emission sources
Diagram showing the main sources of methane for the decade 2008-2017, produced by a global report on global methane emissions by the Global Carbon Project[8]
"Methane global emissions from the five broad categories for the 2008–2017 decade for top-down inversion models and for bottom-up models and inventories (right dark coloured box plots).[8]

Abiogenic methane is stored in rocks and soil stems from the geologic processes that convert ancient biomass into fossil fuels. Biogenic methane is actively produced by microorganisms in a process called methanogenesis. Under certain conditions, the process mix responsible for a sample of methane may be deduced from the ratio of the isotopes of carbon, and through analysis methods similar to carbon dating.[14][15]

Anthropogenic
Map of methane emissions from four source categories[8]

A comprehensive systems method from describing the sources of methane due to human society is known as anthropogenic metabolism. As of year 2020, the emission volumes from some sources remain more uncertain than others; due in part to localized emission spikes not captured by the limited global measurement capability. The time required for a methane emission to become well-mixed throughout earth's troposphere is about 1-2 years.[16]

CategoryMajor SourcesIEA Annual Emission[3]
(Million Tons)
Fossil fuels Gas distribution 45
Oil wells 39*
Coal mines 39
Biofuels Anaerobic digestion 11
Industrial agriculture Enteric fermentation 145
Rice paddies
Manure management
Biomass Biomass burning 16
Consumer waste Solid waste
Landfill gas		 68
Wastewater
Total anthropogenic 363
* An additional 100 million tons (140 billion cubic meters) of gas is vented and flared each year from oil wells.[17]
Additional References: [1][18][19][20][21]

Natural
Map of methane emissions from three natural sources and one sink.[8]

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

CategoryMajor SourcesIEA Annual Emission[3]
(Million Tons)
Wetlands Wetland methane 194
Other natural Geologic seepages
Volcanic gas		 39
Arctic melting
Permafrost
Ocean sediments
Wildfires
Termites
Total natural 233
Additional References: [1][18][19]

Importance of fossil emissions
See also: carbon cycle and atmospheric carbon dioxide
Diagram showing relative sizes (in gigatonnes) of the main storage pools of carbon in Earth's biosphere (year 2015 estimates). Total changes from land use and from industrial emissions of fossil carbon are included for comparison.[22]

Unlike most other natural and human-caused emissions, fossil-fuel extraction and burning yields a net transfer of carbon between major storage pools in Earth's biosphere that will persist for millennia. In total, humans extracted about 400 billion tons (gigatonnes or petagrams) of geologic carbon through year 2015;[23] including half in just the last one-third century[24] and at an increasing rate of about 10 billion tons per year.[25] The magnitude of this transfer exceeds that from any other known geologic event throughout all of human history. About 50 percent of the transferred carbon presently resides in the atmosphere in the form of elevated CO2 and CH4 concentrations, while most of the remainder has been taken up by the oceans as an increase in dissolved CO2 and carbonic acid especially near the water surface.[26] By contrast, the magnitude of the terrestrial sink has remained relatively constant.[25]

This carbon redistribution is the root cause of recent rapid global warming, ocean acidification, and their resulting impacts to life.[27][28] Some of the largest effects, like sea level rise and desertification, occur over time due to the vast inertia of the Earth system. Assessing these and other environmental threats to the sustainability of human civilization are topics within Earth system science, including the recently proposed comprehensive framework of planetary boundaries.[29][30] Despite the probable crossing of multiple boundaries by the early 21st century, there has been very limited international progress towards a corresponding framework or forum for planetary management.

Global monitoring

Uncertainties in methane emissions, including so-called "super-emitter" fossil extractions[31] and unexplained atmospheric fluctuations,[32] highlight the need for improved monitoring at both regional and global scale. Satellites have recently begun to come online with capability to measure methane and other more powerful greenhouse gases with improving resolution.[33][34] The Tropomi[35] instrument launched in year 2017 by the European Space Agency can measure methane, sulphur dioxide, nitrogen dioxide, carbon monoxide, aerosol, and ozone concentrations in earth's troposphere at resolutions of several kilometers.[31][36][37] Japan's GOSAT-2 platform launched in 2018 provides similar capability.[38] The CLAIRE satellite launched in year 2016 by the Canadian firm GHGSat can resolve carbon dioxide and methane to as little as 50 meters, thus enabling its customers to pinpoint the source of emissions.[33]

National reduction policies
Part of a series on the
Carbon cycle
By regions
Carbon dioxide
Carbon types
Metabolic pathways
Carbon pumps
Carbon sequestration
Methane
Biogeochemical
Other
Global anthropogenic methane emissions from historical inventories and future Shared Socioeconomic Pathways (SSP) projections.[8]

China implemented regulations requiring coal plants to either capture methane emissions or convert methane into CO2 in 2010. According to a Nature Communications paper published in January 2019, methane emissions instead increased 50 percent between 2000 and 2015.[39][40]

In March 2020, Exxon called for stricter methane regulations, which would include detection and repair of leaks, minimization of venting and releases of unburned methane, and reporting requirements for companies.[41] However in August 2020, the U.S. Environmental Protection Agency rescinded a prior tightening of methane emission rules for the U.S. oil and gas industry.[42][43]

By country
Methane emissions for 2017 by region, source category, and latitude.[44]
Methane emissions (kt of CO2 equivalent)[45]
Country 1970 2012
 Afghanistan10,20213,763
 Albania1,7642,644
 Algeria12,85748,527
 American Samoa713
 Andorran.a.n.a.
 Angola23,37718,974
 Antigua and Barbuda2443
 Argentina84,91888,476
 Armenia1,3183,426
 Aruba1023
 Australia94,291125,588
 Austria9,0228,007
 Azerbaijan6,39819,955
 Bahamas94227
 Bahrain7913,379
 Bangladesh91,305105,142
 Barbados100109
 Belarus12,12516,620
 Belgium14,1239,243
 Belize96228
 Benin3,4616,983
 Bermuda2031
 Bhutan6981,770
 Bolivia16,50923,231
 Bosnia and Herzegovina3,1743,140
 Botswana5,2324,448
 Brazil207,737477,077
 British Virgin Islands1319
 Brunei Darussalam1,6154,539
 Bulgaria9,94011,794
 Burkina Faso4,61314,957
 Burundi1,4692,719
 Cabo Verde46151
 Cambodia20,08735,915
 Cameroon8,28618,516
 Canada67,296106,847
 Cayman Islands1229
 Central African Republic28,89085,677
 Chad8,04318,364
Channel Islandsn.a.n.a.
 Chile10,91318,381
 China781,0881,752,290
 Colombia36,92167,979
 Comoros142284
 Congo, Dem. Rep.119,58375,336
 Congo, Rep.6,6777,156
 Costa Rica2,5992,315
 Cote d'Ivoire7,80316,266
 Croatia2,9864,708
 Cuba13,6008,560
 Curacaon.a.n.a.
 Cyprus341642
 Czech Republic17,96311,902
 Denmark7,6927,603
 Djibouti149634
 Dominica1641
 Dominican Republic3,7876,861
 Ecuador6,62115,786
 Egypt20,77851,977
 El Salvador2,2393,032
 Equatorial Guinea762,959
 Eritrea1,7972,894
 Estonia2,2082,235
 Ethiopia32,68764,481
 Faroe Islands3039
 Fiji416715
 Finland9,9728,552
 France82,88281,179
 French Polynesia4199
 Gabon8763,894
 Gambia, The4951,039
 Georgia3,4935,019
 Germany126,69255,721
 Ghana5,23021,078
 Gibraltar37
 Greece5,8728,255
 Greenland1829
 Grenada2537
 Guam3071
 Guatemala3,2176,877
 Guinea7,14828,654
 Guinea-Bissau5421,421
 Guyana2,0662,124
 Haiti2,9564,587
 Honduras2,5525,844
 Hong Kong SAR7043,147
 Hungary10,3957,135
 Iceland308359
 India398,212636,396
 Indonesia126,665223,316
 Iran, Islamic Rep.52,013121,298
 Iraq19,68224,351
 Ireland10,17014,330
 Isle of Mann.a.n.a.
 Israel1,3013,416
 Italy40,48835,238
 Jamaica8211,316
 Japan101,80438,957
 Jordan3622,115
 Kazakhstan68,23871,350
 Kenya12,00928,027
 Kiribati516
 North Korea15,00718,983
 Korea, Rep.25,94932,625
 Kosovon.a.n.a.
 Kuwait21,91012,691
 Kyrgyz Republic4,5614,291
 Laos6,97615,011
 Latvia3,3233,181
 Lebanon5451,150
 Lesotho1,1301,287
 Liberia4931,586
 Libya29,69518,495
 Liechtensteinn.a.n.a.
 Lithuania4,5844,806
 Luxembourg7141,169
 Macau49151
 Macedonia2,0331,396
 Madagascar15,19420,070
 Malawi3,1894,629
 Malaysia14,31734,271
 Maldives1352
 Mali8,28118,042
 Malta98141
 Marshall Islands28
 Mauritania3,1576,082
 Mauritius169311
 Mexico60,999116,705
 Micronesia, Fed. Sts.1730
 Moldova2,0683,456
 Monacon.a.n.a.
 Mongolia6,7356,257
 Montenegron.a.n.a.
 Morocco8,48612,012
 Mozambique12,7939,968
 Myanmar75,25480,637
 Namibia4,0045,097
 Nauru13
   Nepal17,36423,982
 Netherlands20,20419,026
 New Caledonia180215
 New Zealand25,05428,658
 Nicaragua4,0076,492
 Niger5,1856,858
 Nigeria35,19689,782
 Northern Mariana Islands212
 Norway6,86616,409
 Oman4,57116,858
 Pakistan56,503158,337
 Palau11
 Panama2,3243,378
 Papua New Guinea9482,143
 Paraguay10,14516,246
 Peru13,70419,321
 Philippines43,21157,170
 Poland97,17465,071
 Portugal6,73112,976
 Puerto Rico1,2772,406
 Qatar4,77641,124
 Romania32,42525,708
 Russian Federation338,496545,819
 Rwanda1,3022,942
 Samoa63133
 San Marinon.a.n.a.
 Sao Tome and Principe1746
 Saudi Arabia31,74062,903
 Senegal4,6059,928
 Serbian.a.n.a.
 Seychelles924
 Sierra Leone2,5543,352
 Singapore6582,386
 Sint Maarten (Dutch part)n.a.n.a.
 Slovak Republic4,5744,075
 Slovenia2,0992,822
 Solomon Islands1,6311,449
 Somalia9,54216,206
 South Africa32,27063,156
 South Sudann.a.n.a.
 Spain26,50937,208
 Sri Lanka11,33811,864
 St. Kitts and Nevis2630
 St. Lucia2844
 Saint Martin (French part)n.a.n.a.
 St. Vincent and the Grenadines2340
 Sudan31,75296,531
 Suriname941709
 Swaziland9211,377
 Sweden10,08210,304
  Switzerland4,8784,900
 Syrian Arab Republic2,42512,783
 Tajikistan2,8145,408
 Tanzania25,21827,994
 Thailand71,444106,499
 Timor-Leste412732
 Togo2,0565,343
 Tonga3261
 Trinidad and Tobago1,59614,789
 Tunisia2,5317,647
 Turkey32,78978,853
 Turkmenistan10,82122,009
 Turks and Caicos Islands16
 Tuvalu23
 Uganda8,56521,161
 Ukraine74,35268,061
 United Arab Emirates12,87326,120
 United Kingdom120,05458,980
 United States594,255499,809
 Uruguay14,52419,549
 Uzbekistan16,83147,333
 Vanuatu128254
 Venezuela35,15158,199
 Vietnam54,145113,564
Virgin Islands (U.S.)1647
 West Bank and Gazan.a.n.a.
 Yemen2,2058,940
 Zambia33,8816,551
 Zimbabwe8,4978,589
World5,305,8208,014,067

Removal technology

In 2019, researchers proposed a technique for removing methane from the atmosphere using zeolite. Each molecule of methane would be converted into CO
2, which has a far smaller impact on climate (99% less). Replacing all atmospheric methane with CO
2 would reduce total greenhouse gas warming by approximately one-sixth.[46]

Zeolite is a crystalline material with a porous molecular structure.[46] Powerful fans could push air through reactors of zeolite and catalysts to absorb the methane. The reactor could then be heated to form and release CO
2. At a carbon price of $500/ton, removing one ton of methane would earn $12,000.[46]

See also

References
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