Editing Global warming potential (section)

=== Current values (IPCC Sixth Assessment Report from 2021) ===
[[File:Global-warming-potential-of-greenhouse-gases-over-100-year-timescale-gwp (OWID 0525).png|thumb|Global warming potential of five greenhouse gases over 100-year timescale.<ref>{{Cite web |title=Global warming potential of greenhouse gases relative to CO2 |url=https://ourworldindata.org/grapher/global-warming-potential-of-greenhouse-gases-over-100-year-timescale-gwp |access-date=2023-12-18 |website=Our World in Data}}</ref>]]The global warming potential (GWP) depends on both the efficiency of the molecule as a greenhouse gas and its atmospheric lifetime. GWP is measured relative to the same mass of {{CO2}} and evaluated for a specific timescale.<ref name=":02">IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf Annex VII: Glossary] [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C.  Méndez, S. Semenov, A. Reisinger (eds.)]. In [https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, [[doi:10.1017/9781009157896.022]].</ref> Thus, if a gas has a high (positive) radiative forcing but also a short lifetime, it will have a large GWP on a 20-year scale but a small one on a 100-year scale. Conversely, if a molecule has a longer atmospheric lifetime than {{CO2}} its GWP will increase when the timescale is considered. Carbon dioxide is defined to have a GWP of 1 over all time periods.

Methane has an atmospheric lifetime of 12 ± 2 years.<ref name="ar6 WG1 Ch 7" />{{rp|Table 7.15}} The [[IPCC Sixth Assessment Report|2021 IPCC report]] lists the GWP as 83 over a time scale of 20 years, 30 over 100 years and 10 over 500 years.<ref name="ar6 WG1 Ch 7" />{{rp|Table 7.15}} The decrease in GWP at longer times is because [[Atmospheric methane#Removal processes|methane]] decomposes to water and {{CO2}} through chemical reactions in the atmosphere. Similarly the third most important GHG, [[nitrous oxide]] (N<sub>2</sub>O), is a common gas emitted through the [[denitrification]] part of the [[nitrogen cycle]].<ref>{{Cite journal |last1=Yang |first1=Rui |last2=Yuan |first2=Lin-jiang |last3=Wang |first3=Ru |last4=He |first4=Zhi-xian |last5=Lei |first5=Lin |last6=Ma |first6=Yan-chen |date=2022 |title=Analyzing the mechanism of nitrous oxide production in aerobic phase of anoxic/aerobic sequential batch reactor from the perspective of key enzymes |url=https://link.springer.com/10.1007/s11356-022-18800-3 |journal=Environmental Science and Pollution Research |language=en |volume=29 |issue=26 |pages=39877–39887 |doi=10.1007/s11356-022-18800-3 |pmid=35113372 |bibcode=2022ESPR...2939877Y |issn=0944-1344|url-access=subscription }}</ref> It has a lifetime of 109 years and an even higher GWP level running at 273 over 20 and 100 years.

Examples of the atmospheric lifetime and GWP relative to {{CO2}} for several greenhouse gases are given in the following table:
{| class="wikitable sortable" style="text-align: right"
|+Atmospheric lifetime and global warming potential (GWP) relative to {{CO2}} at different time horizon for various greenhouse gases (more values provided at global warming potential)
!Gas name
!Chemical 
formula
!Lifetime 
(years)<ref name="ar6 WG1 Ch 7" />{{rp|Table 7.15}}<ref name="TableOfWarmingPotentials5">{{cite book |title=Intergovernmental Panel on Climate Change Fifth Assessment Report |page=731 |chapter=Appendix 8.A |access-date=6 November 2017 |chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf |archive-url=https://web.archive.org/web/20171013100414/http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf |archive-date=13 October 2017 |url-status=live}}</ref>
!Radiative Efficiency 
(Wm{{sup|−2}}ppb{{sup|−1}}, molar basis).<ref name="ar6 WG1 Ch 7" />{{rp|Table 7.15}}<ref name="TableOfWarmingPotentials5" />
!20 year GWP<ref name="ar6 WG1 Ch 7" />{{rp|Table 7.15}}<ref name="TableOfWarmingPotentials5" />
!100 year GWP<ref name="ar6 WG1 Ch 7" />{{rp|Table 7.15}}<ref name="TableOfWarmingPotentials5" />
!500 year GWP<ref name="ar6 WG1 Ch 7" />{{rp|Table 7.15}}<ref name="TableOfWarmingPotentials">{{cite book |title=IPCC Fourth Assessment Report |page=212 |chapter=Table 2.14 |access-date=16 December 2008 |chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf |archive-url=https://web.archive.org/web/20071215200559/http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf |archive-date=15 December 2007 |url-status=live}}</ref>
|-
| style="text-align:left;" |[[Carbon dioxide]]
| style="text-align:center;" |{{CO2}}
|<sup>(A)</sup>
|{{val|1.37e-5}}
|1
|1
|1
|-
| style="text-align:left;" |[[Methane]] (fossil [[natural gas]])
| style="text-align:center;" |{{chem|CH|4}}
|12
|{{val|5.7e-4}}
|83
|30
|10
|-
| style="text-align:left;" |[[Methane]] (pure non-fossil)
| style="text-align:center;" |{{chem|CH|4}}
|12
|{{val|5.7e-4}}
|81
|27
|7.3
|- id="N2O"
| style="text-align:left;" |[[Nitrous oxide]]
| style="text-align:center;" |{{chem|N|2|O}}
|109
|{{val|3e-3}}
|273
|273
|130
|-
| style="text-align:left;" |[[CFC-11]] (R-11)
| style="text-align:center;" |{{chem|CCl|3|F}}
|52
|{{val|0.29}}
|8321
|6226
|2093
|-
| style="text-align:left;" |[[CFC-12]] (R-12)
| style="text-align:center;" |{{chem|CCl|2|F|2}}
|100
|{{val|0.32}}
|10800
|10200
|5200
|-
| style="text-align:left;" |[[HCFC-22]] (R-22)
| style="text-align:center;" |{{chem|CHClF|2}}
|12
|{{val|0.21}}
|5280
|1760
|549
|-
| style="text-align:left;" |[[HFC-32]] (R-32)
| style="text-align:center;" |{{chem|CH|2|F|2}}
|5
|{{val|0.11}}
|2693
|771
|220
|-
| style="text-align:left;" |[[HFC-134a]] (R-134a)
| style="text-align:center;" |{{chem|CH|2|FCF|3}}
|14
|{{val|0.17}}
|4144
|1526
|436
|-
| style="text-align:left;" |[[Tetrafluoromethane]] (R-14)
| style="text-align:center;" |{{chem|CF|4}}
|50000
|{{val|0.09}}
|5301
|7380
|10587
|-
| style="text-align:left;" |[[Hexafluoroethane]]
| style="text-align:center;" |{{chem|C|2|F|6}}
|10000
|{{val|0.25}}
|8210
|11100
|18200
|-
| style="text-align:left;" |[[Sulfur hexafluoride]]
| style="text-align:center;" |{{chem|SF|6}}
|3200
|{{val|0.57}}
|17500
|23500
|32600
|-
| style="text-align:left;" |[[Nitrogen trifluoride]]
| style="text-align:center;" |{{chem|NF|3}}
|500
|{{val|0.20}}
|12800
|16100
|20700
|-
! colspan="7" |<small><sup>(A)</sup> No single lifetime for atmospheric {{CO2}} can be given.</small>
|}
Estimates of GWP values over 20, 100 and 500 years are periodically compiled and revised in reports from the [[Intergovernmental Panel on Climate Change]]. The most recent report is the [[IPCC Sixth Assessment Report]] (Working Group I) from 2023.<ref name="ar6 WG1 Ch 7">Forster, P., T. Storelvmo, K. Armour, W. Collins, J.-L. Dufresne, D. Frame, D.J. Lunt, T. Mauritsen, M.D. Palmer, M. Watanabe, M. Wild, and H. Zhang, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter07.pdf Chapter 7: The Earth's Energy Budget, Climate Feedbacks, and Climate Sensitivity]. In https://www.ipcc.ch/report/ar6/wg1/ [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N.  Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 923–1054, doi:10.1017/9781009157896.009.</ref>

The IPCC lists many other substances not shown here.<ref name="ar5">{{Harvnb|IPCC AR5 WG1 Ch8|2013|pages=714, 731}}.</ref><ref name="ar6 WG1 Ch 7" /><ref> {{cite web |title= IPCC Sixth Assessment Report: The Physical Science Basis Ch7.Supp Mat Table 7
|url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_FGD_Chapter07_SM.pdf
|archive-url=https://web.archive.org/web/20240630195210/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_FGD_Chapter07_SM.pdf 
|archive-date=30 June 2024}}</ref> Some have high GWP but only a low concentration in the atmosphere.

The values given in the table assume the same mass of compound is analyzed; different ratios will result from the conversion of one substance to another. For instance, burning [[methane]] to carbon dioxide would reduce the global warming impact, but by a smaller factor than 25:1 because the mass of [[methane]] burned is less than the mass of [[carbon dioxide]] released (ratio 1:2.74).<ref>This is so, because of the reaction formula: CH<sub>4</sub> + 2O<sub>2</sub> → {{CO2}} + 2 H<sub>2</sub>O. As mentioned in the article, the oxygen and water is not considered for GWP purposes, and one molecule of methane (molar mass = 16.04 g mol<sup>−1</sup>) will yield one molecule of carbon dioxide (molar mass = 44.01 g mol<sup>−1</sup>). This gives a mass ratio of 2.74. (44.01/16.04 ≈ 2.74).</ref> For a starting amount of 1 tonne of methane, which has a GWP of 25, after combustion there would be 2.74 tonnes of {{CO2}}, each tonne of which has a GWP of 1. This is a net reduction of 22.26 tonnes of GWP, reducing the global warming effect by a ratio of 25:2.74 (approximately 9 times).

{| class="wikitable sortable"
! rowspan="2" | Greenhouse gas
! rowspan="2" data-sort-type="number" | Lifetime <br />(years)
! colspan="3" | Global warming potential, GWP
|-
! data-sort-type="number" | 20 years
! data-sort-type="number" | 100 years
! data-sort-type="number" | 500 years
|-
|[[Hydrogen]] (H<sub>2</sub>)
|4–7<ref name=":3">{{Cite report |url=https://www.gov.uk/government/publications/atmospheric-implications-of-increased-hydrogen-use |title=Atmospheric implications of increased hydrogen use |last1=Warwick |first1=Nicola |last2=Griffiths |first2=Paul |date=2022-04-08 |publisher=UK Department for Business, Energy & Industrial Strategy (BEIS) |last3=Keeble |first3=James |last4=Archibald |first4=Alexander |last5=John |first5=Pile |ref={{Harvid|Warwick|2022}}}}</ref>
| data-sort-value="33" | 33 (20–44)<ref name=":3" />
| data-sort-value="11" | 11 (6–16)<ref name=":3" />|| {{n/a}}
|-
|[[Methane]] ({{CH4}})
|11.8<ref name="ar6 WG1 Ch 7" />
| data-sort-value="70" |56<ref name="sar">{{Harvnb|IPCC SAR WG1 Ch2|1995|p=121}}.</ref><br />72<ref name="ar4">{{Harvnb|IPCC AR4 WG1 Ch2|2007|p=212}}.</ref><br />84 / 86f<ref name="ar5" /><br />96<ref>{{Cite journal |last=Alvarez |date=2018 |title=Assessment of methane emissions from the U.S. oil and gas supply chain |url=http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=924889 |journal=Science |volume=361 |issue=6398 |pages=186–188 |bibcode=2018Sci...361..186A |doi=10.1126/science.aar7204 |pmc=6223263 |pmid=29930092}}</ref><br />80.8 (biogenic)<ref name="ar6 WG1 Ch 7" /><br /> 82.5 (fossil)<ref name="ar6 WG1 Ch 7" />
| data-sort-value="30" |21<ref name="sar" /><br />25<ref name="ar4" /><br />28 / 34f<ref name="ar5" /><br />32<ref>{{cite journal |last1=Etminan |first1=M. |last2=Myhre |first2=G. |last3=Highwood |first3=E. J. |last4=Shine |first4=K. P. |date=28 December 2016 |title=Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing |journal=Geophysical Research Letters |volume=43 |issue=24 |bibcode=2016GeoRL..4312614E |doi=10.1002/2016GL071930 |doi-access=free}}</ref><br />39 (biogenic)<ref name=":4">{{cite news |last1=Morton |first1=Adam |date=26 August 2020 |title=Methane released in gas production means Australia's emissions may be 10% higher than reported |work=The Guardian |url=https://www.theguardian.com/environment/2020/aug/26/methane-released-in-gas-production-means-australias-emissions-may-be-10-higher-than-reported}}</ref><br />40 (fossil)<ref name=":4" />
| data-sort-value="7" |6.5<ref name="sar" /><br />7.6<ref name="ar4" />
|-
|[[Nitrous oxide]] ({{N2O}})
|109<ref name="ar6 WG1 Ch 7" />
| data-sort-value="270" |280<ref name="sar" /><br />289<ref name="ar4" /><br />264 / 268f<ref name="ar5" /><br />273<ref name="ar6 WG1 Ch 7" />
| data-sort-value="300" |310<ref name="sar" /><br />298<ref name="ar4" /><br />265 / 298f<ref name="ar5" /><br />273<ref name="ar6 WG1 Ch 7" />
| data-sort-value="160" |170<ref name="sar" /><br />153<ref name="ar4" /><br />130<ref name="ar6 WG1 Ch 7" />
|-
|[[HFC-134a]] ([[hydrofluorocarbon]])
|14.0<ref name="ar6 WG1 Ch 7" />
| data-sort-value="4000" |3,710 / 3,790f<ref name="ar5" /><br />4,144<ref name="ar6 WG1 Ch 7" />
| data-sort-value="1500" |1,300 / 1,550f<ref name="ar5" /><br />1,526<ref name="ar6 WG1 Ch 7" />
| data-sort-value="435" |435<ref name="ar4" /><br />436<ref name="ar6 WG1 Ch 7" />
|-
|[[CFC-11]] ([[chlorofluorocarbon]])
|52.0<ref name="ar6 WG1 Ch 7" />
| data-sort-value="7000" |6,900 / 7,020f<ref name="ar5" /><br />8,321<ref name="ar6 WG1 Ch 7" />
| data-sort-value="5000" |4,660 / 5,350f<ref name="ar5" /><br />6,226<ref name="ar6 WG1 Ch 7" />
| data-sort-value="2000" |1,620<ref name="ar4" /><br />2,093<ref name="ar6 WG1 Ch 7" />
|-
|[[Carbon tetrafluoride]] (CF{{sub|4}} / PFC-14)
|50,000<ref name="ar6 WG1 Ch 7" />
| data-sort-value="5000" |4,880 / 4,950f<ref name="ar5" /><br />5,301<ref name="ar6 WG1 Ch 7" />
| data-sort-value="7000" |6,630 / 7,350f<ref name="ar5" /><br />7,380<ref name="ar6 WG1 Ch 7" />
| data-sort-value="11000" |11,200<ref name="ar4" /><br />10,587<ref name="ar6 WG1 Ch 7" />
|-
| [[HFC-23]] ([[hydrofluorocarbon]])
|222<ref name="ar5" />
| data-sort-value="11000" |12,000<ref name="ar4" /><br />10,800<ref name="ar5" />
| data-sort-value="13000" |14,800<ref name="ar4" /><br />12,400<ref name="ar5" />
| data-sort-value="12200" |12,200<ref name="ar4" />
|-
|[[Sulfur hexafluoride]] {{chem2|SF6}}
|3,200<ref name="ar5" />
| data-sort-value="17000" |16,300<ref name="ar4" /><br />17,500<ref name="ar5" />
| data-sort-value="23000" |22,800<ref name="ar4" /><br />23,500<ref name="ar5" />
| data-sort-value="32600" |32,600<ref name="ar4" />
|}