Methane emissions

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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%)

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]

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[edit]

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[edit]

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[edit]

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]

Category Major Sources IEA 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[edit]

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.

Category Major Sources IEA 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[edit]

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[edit]

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[edit]

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[edit]

Methane emissions for 2017 by region, source category, and latitude.[44]
Methane emissions (kt of CO2 equivalent)[45]
Country 1970 2012
 Afghanistan 10,202 13,763
 Albania 1,764 2,644
 Algeria 12,857 48,527
 American Samoa 7 13
 Andorra n.a. n.a.
 Angola 23,377 18,974
 Antigua and Barbuda 24 43
 Argentina 84,918 88,476
 Armenia 1,318 3,426
 Aruba 10 23
 Australia 94,291 125,588
 Austria 9,022 8,007
 Azerbaijan 6,398 19,955
 Bahamas 94 227
 Bahrain 791 3,379
 Bangladesh 91,305 105,142
 Barbados 100 109
 Belarus 12,125 16,620
 Belgium 14,123 9,243
 Belize 96 228
 Benin 3,461 6,983
 Bermuda 20 31
 Bhutan 698 1,770
 Bolivia 16,509 23,231
 Bosnia and Herzegovina 3,174 3,140
 Botswana 5,232 4,448
 Brazil 207,737 477,077
 British Virgin Islands 13 19
 Brunei Darussalam 1,615 4,539
 Bulgaria 9,940 11,794
 Burkina Faso 4,613 14,957
 Burundi 1,469 2,719
 Cabo Verde 46 151
 Cambodia 20,087 35,915
 Cameroon 8,286 18,516
 Canada 67,296 106,847
 Cayman Islands 12 29
 Central African Republic 28,890 85,677
 Chad 8,043 18,364
Channel Islands n.a. n.a.
 Chile 10,913 18,381
 China 781,088 1,752,290
 Colombia 36,921 67,979
 Comoros 142 284
 Congo, Dem. Rep. 119,583 75,336
 Congo, Rep. 6,677 7,156
 Costa Rica 2,599 2,315
 Cote d'Ivoire 7,803 16,266
 Croatia 2,986 4,708
 Cuba 13,600 8,560
 Curacao n.a. n.a.
 Cyprus 341 642
 Czech Republic 17,963 11,902
 Denmark 7,692 7,603
 Djibouti 149 634
 Dominica 16 41
 Dominican Republic 3,787 6,861
 Ecuador 6,621 15,786
 Egypt 20,778 51,977
 El Salvador 2,239 3,032
 Equatorial Guinea 76 2,959
 Eritrea 1,797 2,894
 Estonia 2,208 2,235
 Ethiopia 32,687 64,481
 Faroe Islands 30 39
 Fiji 416 715
 Finland 9,972 8,552
 France 82,882 81,179
 French Polynesia 41 99
 Gabon 876 3,894
 Gambia, The 495 1,039
 Georgia 3,493 5,019
 Germany 126,692 55,721
 Ghana 5,230 21,078
 Gibraltar 3 7
 Greece 5,872 8,255
 Greenland 18 29
 Grenada 25 37
 Guam 30 71
 Guatemala 3,217 6,877
 Guinea 7,148 28,654
 Guinea-Bissau 542 1,421
 Guyana 2,066 2,124
 Haiti 2,956 4,587
 Honduras 2,552 5,844
 Hong Kong SAR 704 3,147
 Hungary 10,395 7,135
 Iceland 308 359
 India 398,212 636,396
 Indonesia 126,665 223,316
 Iran, Islamic Rep. 52,013 121,298
 Iraq 19,682 24,351
 Ireland 10,170 14,330
 Isle of Man n.a. n.a.
 Israel 1,301 3,416
 Italy 40,488 35,238
 Jamaica 821 1,316
 Japan 101,804 38,957
 Jordan 362 2,115
 Kazakhstan 68,238 71,350
 Kenya 12,009 28,027
 Kiribati 5 16
 North Korea 15,007 18,983
 Korea, Rep. 25,949 32,625
 Kosovo n.a. n.a.
 Kuwait 21,910 12,691
 Kyrgyz Republic 4,561 4,291
 Laos 6,976 15,011
 Latvia 3,323 3,181
 Lebanon 545 1,150
 Lesotho 1,130 1,287
 Liberia 493 1,586
 Libya 29,695 18,495
 Liechtenstein n.a. n.a.
 Lithuania 4,584 4,806
 Luxembourg 714 1,169
 Macau 49 151
 Macedonia 2,033 1,396
 Madagascar 15,194 20,070
 Malawi 3,189 4,629
 Malaysia 14,317 34,271
 Maldives 13 52
 Mali 8,281 18,042
 Malta 98 141
 Marshall Islands 2 8
 Mauritania 3,157 6,082
 Mauritius 169 311
 Mexico 60,999 116,705
 Micronesia, Fed. Sts. 17 30
 Moldova 2,068 3,456
 Monaco n.a. n.a.
 Mongolia 6,735 6,257
 Montenegro n.a. n.a.
 Morocco 8,486 12,012
 Mozambique 12,793 9,968
 Myanmar 75,254 80,637
 Namibia 4,004 5,097
 Nauru 1 3
   Nepal 17,364 23,982
 Netherlands 20,204 19,026
 New Caledonia 180 215
 New Zealand 25,054 28,658
 Nicaragua 4,007 6,492
 Niger 5,185 6,858
 Nigeria 35,196 89,782
 Northern Mariana Islands 2 12
 Norway 6,866 16,409
 Oman 4,571 16,858
 Pakistan 56,503 158,337
 Palau 1 1
 Panama 2,324 3,378
 Papua New Guinea 948 2,143
 Paraguay 10,145 16,246
 Peru 13,704 19,321
 Philippines 43,211 57,170
 Poland 97,174 65,071
 Portugal 6,731 12,976
 Puerto Rico 1,277 2,406
 Qatar 4,776 41,124
 Romania 32,425 25,708
 Russian Federation 338,496 545,819
 Rwanda 1,302 2,942
 Samoa 63 133
 San Marino n.a. n.a.
 Sao Tome and Principe 17 46
 Saudi Arabia 31,740 62,903
 Senegal 4,605 9,928
 Serbia n.a. n.a.
 Seychelles 9 24
 Sierra Leone 2,554 3,352
 Singapore 658 2,386
 Sint Maarten (Dutch part) n.a. n.a.
 Slovak Republic 4,574 4,075
 Slovenia 2,099 2,822
 Solomon Islands 1,631 1,449
 Somalia 9,542 16,206
 South Africa 32,270 63,156
 South Sudan n.a. n.a.
 Spain 26,509 37,208
 Sri Lanka 11,338 11,864
 St. Kitts and Nevis 26 30
 St. Lucia 28 44
 Saint Martin (French part) n.a. n.a.
 St. Vincent and the Grenadines 23 40
 Sudan 31,752 96,531
 Suriname 941 709
 Swaziland 921 1,377
 Sweden 10,082 10,304
  Switzerland 4,878 4,900
 Syrian Arab Republic 2,425 12,783
 Tajikistan 2,814 5,408
 Tanzania 25,218 27,994
 Thailand 71,444 106,499
 Timor-Leste 412 732
 Togo 2,056 5,343
 Tonga 32 61
 Trinidad and Tobago 1,596 14,789
 Tunisia 2,531 7,647
 Turkey 32,789 78,853
 Turkmenistan 10,821 22,009
 Turks and Caicos Islands 1 6
 Tuvalu 2 3
 Uganda 8,565 21,161
 Ukraine 74,352 68,061
 United Arab Emirates 12,873 26,120
 United Kingdom 120,054 58,980
 United States 594,255 499,809
 Uruguay 14,524 19,549
 Uzbekistan 16,831 47,333
 Vanuatu 128 254
 Venezuela 35,151 58,199
 Vietnam 54,145 113,564
Virgin Islands (U.S.) 16 47
 West Bank and Gaza n.a. n.a.
 Yemen 2,205 8,940
 Zambia 33,881 6,551
 Zimbabwe 8,497 8,589
World 5,305,820 8,014,067

Removal technology[edit]

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[edit]

References[edit]

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External links[edit]