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 global heating.[1][2] During 2019, about 60% (360 million tons) of methane released globally was from human activities, while natural sources contributed about 40% (230 million tons).[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%)
  Waste (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 hydrocarbon and clathrate hydrate deposits, 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 influenceEdit

 
Globally averaged atmospheric CH4 (upper graph) and its annual growth rate (lower graph)[8]

The atmospheric methane (CH4) concentration is increasing and exceeded 1860 parts per billion in 2019, equal to two-and-a-half times the pre-industrial level.[9] The methane itself causes 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, themselves potent warming gases: atmospheric researchers call this amplification of methane's near-term warming influence 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 global heating.[1][2]

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 much longer, assuming no change in rates of carbon sequestration.[12][13] The global warming potential (GWP) is a way of comparing the warming due to other gases to that from carbon dioxide, over a given time period. Methane's GWP20 of 85 means 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.[13] On a 100-year timescale, methane's GWP100 is in the range of 28–34.

List of emission sourcesEdit

 
The main sources of methane for the decade 2008–2017, estimated 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][clarification needed]

Abiogenic methane is stored in rocks and soil stems from the geologic processes that convert ancient biomass into fossil fuels.[clarification needed][contradictory] 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]

AnthropogenicEdit

 
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.[clarification needed] As of 2020, 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]

NaturalEdit

 
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 emissionsEdit

 
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 monitoringEdit

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 policiesEdit

 
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 countryEdit

 
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 technologyEdit

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
. Because of methane's higher GWP, at a carbon price of $500/ton removing one ton of methane would earn $12,000.[46]

See alsoEdit

ReferencesEdit

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External linksEdit