Global warming potential

Global warming potential(GWP) is an index to measure how muchinfrared thermal radiationagreenhouse gaswould absorb over a given time frame after it has been added to theatmosphere(oremittedto the atmosphere). The GWP makes different greenhouse gases comparable with regard to their "effectiveness in causingradiative forcing".^[1]^: 2232It is expressed as a multiple of the radiation that would be absorbed by the samemassof addedcarbon dioxide(CO₂), which is taken as a reference gas. Therefore, the GWP has a value of 1 for CO₂.For othergasesit depends on how strongly the gas absorbs infrared thermal radiation, how quickly the gas leaves the atmosphere, and the time frame being considered.

For example,methanehas a GWP over 20 years (GWP-20) of 81.2^[2]meaning that, for example, aleakof a tonne of methane is equivalent to emitting 81.2 tonnes of carbon dioxide measured over 20 years. As methane has a much shorter atmospheric lifetime than carbon dioxide, its GWP is much less over longer time periods, with a GWP-100 of 27.9 and a GWP-500 of 7.95.^[2]^: 7SM-24

Thecarbon dioxide equivalent(CO₂e or CO₂eq or CO₂-e or CO₂-eq) can be calculated from the GWP. For any gas, it is the mass of CO₂that would warm the earth as much as the mass of that gas. Thus it provides a common scale for measuring theclimate effectsof different gases. It is calculated as GWP times mass of the other gas.

Definition

The global warming potential (GWP) is defined as an "index measuring theradiative forcingfollowing an emission of a unit mass of a given substance, accumulated over a chosen time horizon, relative to that of the reference substance, carbon dioxide (CO₂). The GWP thus represents the combined effect of the differing times these substances remain in the atmosphere and their effectiveness in causing radiative forcing. "^[1]^: 2232

In turn,radiative forcingis a scientific concept used to quantify and compare the external drivers of change toEarth's energy balance.^[3]^: 1–4Radiative forcing is the change inenergy fluxin the atmosphere caused bynaturaloranthropogenicfactors ofclimate changeas measured inwattsper meter squared.^[4]

GWP in policymaking

As governments develop policies to combat emissions from high-GWP sources, policymakers have chosen to use the 100-year GWP scale as the standard in international agreements. TheKigali Amendmentto theMontreal Protocolsets the global phase-down ofhydrofluorocarbons(HFCs), a group of high-GWP compounds. It requires countries to use a set of GWP100 values equal to those published in the IPCC’s Fourth Assessment Report (AR4).^[5]This allows policymakers to have one standard for comparison instead of changing GWP values in new assessment reports.^[6]One exception to the GWP100 standard exists:New York state’sClimate Leadership and Community Protection Actrequires the use of GWP20, despite being a different standard from all other countries participating in phase downs of HFCs.^[5]

Calculated values

Current values (IPCC Sixth Assessment Report from 2021)

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 CO₂and evaluated for a specific timescale.^[8]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 CO₂its 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.^[9]^{: Table 7.15}The2021 IPCC reportlists the GWP as 83 over a time scale of 20 years, 30 over 100 years and 10 over 500 years.^[9]^{: Table 7.15}The decrease in GWP at longer times is becausemethanedecomposes to water and CO₂through chemical reactions in the atmosphere. Similarly the third most important GHG,nitrous oxide(N₂O), is a common gas emitted through thedenitrificationpart of thenitrogen cycle.^[10]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 CO₂for several greenhouse gases are given in the following table:

Atmospheric lifetime and global warming potential (GWP) relative to CO₂at different time horizon for various greenhouse gases (more values provided at global warming potential)
Gas name	Chemical formula	Lifetime (years)^[9]^{: Table 7.15}^[11]	Radiative Efficiency (Wm⁻²ppb⁻¹,molar basis).^[9]^{: Table 7.15}^[11]	Global warming potential (GWP) for given time horizon
Gas name	Chemical formula	Lifetime (years)^[9]^{: Table 7.15}^[11]		20-yr.^[9]^{: Table 7.15}^[11]	100-yr.^[9]^{: Table 7.15}^[11]	500-yr.^[9]^{: Table 7.15}^[12]
Carbon dioxide	CO₂	^(A)	1.37×10⁻⁵	1	1	1
Methane(fossil)	CH ₄	12	5.7×10⁻⁴	83	30	10
Methane(non-fossil)	CH ₄	12	5.7×10⁻⁴	81	27	7.3
Nitrous oxide	N ₂O	109	3×10⁻³	273	273	130
CFC-11	CCl ₃F	52	0.29	8 321	6 226	2 093
CFC-12	CCl ₂F ₂	100	0.32	10 800	10 200	5 200
HCFC-22(=R22)	CHClF ₂	12	0.21	5 280	1 760	549
HFC-32(= R32)	CH ₂F ₂	5	0.11	2 693	771	220
HFC-134a	CH ₂FCF ₃	14	0.17	4 144	1 526	436
Tetrafluoromethane(R14)	CF ₄	50 000	0.09	5 301	7 380	10 587
Hexafluoroethane	C ₂F ₆	10 000	0.25	8 210	11 100	18 200
Sulfur hexafluoride	SF ₆	3 200	0.57	17 500	23 500	32 600
Nitrogen trifluoride	NF ₃	500	0.20	12 800	16 100	20 700
^(A)No single lifetime for atmospheric CO₂can be given.

Estimates of GWP values over 20, 100 and 500 years are periodically compiled and revised in reports from theIntergovernmental Panel on Climate Change.The most recent report is theIPCC Sixth Assessment Report(Working Group I) from 2023.^[9]

The IPCC lists many other substances not shown here.^[13]^[9]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, burningmethaneto carbon dioxide would reduce the global warming impact, but by a smaller factor than 25:1 because the mass ofmethaneburned is less than the mass ofcarbon dioxidereleased (ratio 1:2.74).^[14]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).

Greenhouse gas	Lifetime (years)	Global warming potential, GWP
Greenhouse gas	Lifetime (years)	20 years	100 years	500 years
Hydrogen(H₂)	4–7^[15]	33 (20-44)^[15]	11 (6–16)^[15]	—
Methane(CH₄)	11.8^[9]	56^[16] 72^[17] 84 / 86f^[13] 96^[18] 80.8 (biogenic)^[9] 82.5 (fossil)^[9]	21^[16] 25^[17] 28 / 34f^[13] 32^[19] 39 (biogenic)^[20] 40 (fossil)^[20]	6.5^[16] 7.6^[17]
Nitrous oxide(N₂O)	109^[9]	280^[16] 289^[17] 264 / 268f^[13] 273^[9]	310^[16] 298^[17] 265 / 298f^[13] 273^[9]	170^[16] 153^[17] 130^[9]
HFC-134a(hydrofluorocarbon)	14.0^[9]	3,710 / 3,790f^[13] 4,144^[9]	1,300 / 1,550f^[13] 1,526^[9]	435^[17] 436^[9]
CFC-11(chlorofluorocarbon)	52.0^[9]	6,900 / 7,020f^[13] 8,321^[9]	4,660 / 5,350f^[13] 6,226^[9]	1,620^[17] 2,093^[9]
Carbon tetrafluoride(CF₄/ PFC-14)	50,000^[9]	4,880 / 4,950f^[13] 5,301^[9]	6,630 / 7,350f^[13] 7,380^[9]	11,200^[17] 10,587^[9]
HFC-23(hydrofluorocarbon)	222^[13]	12,000^[17] 10,800^[13]	14,800^[17] 12,400^[13]	12,200^[17]
Sulfur hexafluorideSF₆	3,200^[13]	16,300^[17] 17,500^[13]	22,800^[17] 23,500^[13]	32,600^[17]

Earlier values from 2007

The values provided in the table below are from 2007 when they were published in theIPCC Fourth Assessment Report.^[21]^[17]These values are still used (as of 2020) for some comparisons.^[22]

Greenhouse gas	Chemical formula	100-year Global warming potentials (2007 estimates, for 2013–2020 comparisons)
Carbon dioxide	CO₂	1
Methane	CH₄	25
Nitrous oxide	N₂O	298
Hydrofluorocarbons (HFCs)
HFC-23	CHF₃	14,800
Difluoromethane(HFC-32)	CH₂F₂	675
Fluoromethane(HFC-41)	CH₃F	92
HFC-43-10mee	CF₃CHFCHFCF₂CF₃	1,640
Pentafluoroethane(HFC-125)	C₂HF₅	3,500
HFC-134	C₂H₂F₄(CHF₂CHF₂)	1,100
1,1,1,2-Tetrafluoroethane(HFC-134a)	C₂H₂F₄(CH₂FCF₃)	1,430
HFC-143	C₂H₃F₃(CHF₂CH₂F)	353
1,1,1-Trifluoroethane(HFC-143a)	C₂H₃F₃(CF₃CH₃)	4,470
HFC-152	CH₂FCH₂F	53
HFC-152a	C₂H₄F₂(CH₃CHF₂)	124
HFC-161	CH₃CH₂F	12
1,1,1,2,3,3,3-Heptafluoropropane(HFC-227ea)	C₃HF₇	3,220
HFC-236cb	CH₂FCF₂CF₃	1,340
HFC-236ea	CHF₂CHFCF₃	1,370
HFC-236fa	C₃H₂F₆	9,810
HFC-245ca	C₃H₃F₅	693
HFC-245fa	CHF₂CH₂CF₃	1,030
HFC-365mfc	CH₃CF₂CH₂CF₃	794
Perfluorocarbons
Carbon tetrafluoride– PFC-14	CF₄	7,390
Hexafluoroethane– PFC-116	C₂F₆	12,200
Octafluoropropane– PFC-218	C₃F₈	8,830
Perfluorobutane– PFC-3-1-10	C₄F₁₀	8,860
Octafluorocyclobutane– PFC-318	c-C₄F₈	10,300
Perfluouropentane– PFC-4-1-12	C₅F₁₂	9,160
Perfluorohexane– PFC-5-1-14	C₆F₁₄	9,300
Perfluorodecalin– PFC-9-1-18b	C₁₀F₁₈	7,500
Perfluorocyclopropane	c-C₃F₆	17,340
Sulfur hexafluoride(SF₆)
Sulfur hexafluoride	SF₆	22,800
Nitrogen trifluoride(NF₃)
Nitrogen trifluoride	NF₃	17,200
Fluorinated ethers
HFE-125	CHF₂OCF₃	14,900
Bis(difluoromethyl) ether(HFE-134)	CHF₂OCHF₂	6,320
HFE-143a	CH₃OCF₃	756
HCFE-235da2	CHF₂OCHClCF₃	350
HFE-245cb2	CH₃OCF₂CF₃	708
HFE-245fa2	CHF₂OCH₂CF₃	659
HFE-254cb2	CH₃OCF₂CHF₂	359
HFE-347mcc3	CH₃OCF₂CF₂CF₃	575
HFE-347pcf2	CHF₂CF₂OCH₂CF₃	580
HFE-356pcc3	CH₃OCF₂CF₂CHF₂	110
HFE-449sl (HFE-7100)	C₄F₉OCH₃	297
HFE-569sf2 (HFE-7200)	C₄F9OC₂H₅	59
HFE-43-10pccc124 (H-Galden 1040x)	CHF₂OCF₂OC₂F₄OCHF₂	1,870
HFE-236ca12 (HG-10)	CHF₂OCF₂OCHF₂	2,800
HFE-338pcc13 (HG-01)	CHF₂OCF₂CF₂OCHF₂	1,500
	(CF₃)₂CFOCH₃	343
	CF₃CF₂CH₂OH	42
	(CF₃)₂CHOH	195
HFE-227ea	CF₃CHFOCF₃	1,540
HFE-236ea2	CHF₂OCHFCF₃	989
HFE-236fa	CF₃CH₂OCF₃	487
HFE-245fa1	CHF₂CH₂OCF₃	286
HFE-263fb2	CF₃CH₂OCH₃	11
HFE-329mcc2	CHF₂CF₂OCF₂CF₃	919
HFE-338mcf2	CF₃CH₂OCF₂CF₃	552
HFE-347mcf2	CHF₂CH₂OCF₂CF₃	374
HFE-356mec3	CH₃OCF₂CHFCF₃	101
HFE-356pcf2	CHF₂CH₂OCF₂CHF₂	265
HFE-356pcf3	CHF₂OCH₂CF₂CHF₂	502
HFE-365mcfI’ll t3	CF₃CF₂CH₂OCH₃	11
HFE-374pc2	CHF₂CF₂OCH₂CH₃	557
	– (CF₂)₄CH (OH) –	73
	(CF₃)₂CHOCHF₂	380
	(CF₃)₂CHOCH₃	27
Perfluoropolyethers
PFPMIE	CF₃OCF(CF₃)CF₂OCF₂OCF₃	10,300
Trifluoromethyl sulfur pentafluoride	SF₅CF₃	17,400

Importance of time horizon

A substance's GWP depends on the number of years (denoted by a subscript) over which the potential is calculated. A gas which is quickly removed from the atmosphere may initially have a large effect, but for longer time periods, as it has been removed, it becomes less important. Thus methane has a potential of 25 over 100 years (GWP₁₀₀= 25) but 86 over 20 years (GWP₂₀= 86); converselysulfur hexafluoridehas a GWP of 22,800 over 100 years but 16,300 over 20 years (IPCC Third Assessment Report). The GWP value depends on how the gas concentration decays over time in the atmosphere. This is often not precisely known and hence the values should not be considered exact. For this reason when quoting a GWP it is important to give a reference to the calculation.

The GWP for a mixture of gases can be obtained from the mass-fraction-weighted average of the GWPs of the individual gases.^[23]

Commonly, a time horizon of 100 years is used by regulators.^[24]^[25]

Water vapour

Water vapourdoes contribute to anthropogenic global warming, but as the GWP is defined, it is negligible for H₂O: an estimate gives a 100-year GWP between -0.001 and 0.0005.^[26]

H₂O can function as a greenhouse gas because it has a profound infrared absorption spectrum with more and broader absorption bands than CO₂.Its concentration in the atmosphere is limited by air temperature, so that radiative forcing by water vapour increases with global warming (positive feedback). But the GWP definition excludes indirect effects. GWP definition is also based on emissions, and anthropogenic emissions of water vapour (cooling towers,irrigation) are removed viaprecipitationwithin weeks, so its GWP is negligible.

Calculation methods

When calculating the GWP of a greenhouse gas, the value depends on the following factors:

the absorption ofinfrared radiationby the given gas
the time horizon of interest (integration period)
theatmospheric lifetimeof the gas

A high GWP correlates with a large infrared absorption and a long atmospheric lifetime. The dependence of GWP on the wavelength of absorption is more complicated. Even if a gas absorbs radiation efficiently at a certain wavelength, this may not affect its GWP much, if the atmosphere already absorbs most radiation at that wavelength. A gas has the most effect if it absorbs in a "window" of wavelengths where the atmosphere is fairly transparent. The dependence of GWP as a function of wavelength has been found empirically and published as a graph.^[30]

Because the GWP of a greenhouse gas depends directly on its infrared spectrum, the use ofinfrared spectroscopyto study greenhouse gases is centrally important in the effort to understand the impact of human activities on globalclimate change.

Just asradiative forcingprovides a simplified means of comparing the various factors that are believed to influence the climate system to one another, global warming potentials (GWPs) are one type of simplified index based upon radiative properties that can be used to estimate the potential future impacts of emissions of different gases upon the climate system in a relative sense. GWP is based on a number of factors, including the radiative efficiency (infrared-absorbing ability) of each gas relative to that of carbon dioxide, as well as the decay rate of each gas (the amount removed from the atmosphere over a given number of years) relative to that of carbon dioxide.^[31]

Theradiative forcing capacity(RF) is the amount of energy per unit area, per unit time, absorbed by the greenhouse gas, that would otherwise be lost to space. It can be expressed by the formula:

${\mathit {RF}}=\sum _{i=1}^{100}{\text{abs}}_{i}\cdot F_{i}/\left({\text{l}}\cdot {\text{d}}\right)$ where the subscriptirepresents awavenumberinterval of 10inverse centimeters.Abs_irepresents the integrated infrared absorbance of the sample in that interval, and F_irepresents the RF for that interval.^{[citation needed]}

TheIntergovernmental Panel on Climate Change(IPCC) provides the generally accepted values for GWP, which changed slightly between 1996 and 2001, except for methane, which had its GWP almost doubled. An exact definition of how GWP is calculated is to be found in the IPCC's 2001 Third Assessment Report.^[32]The GWP is defined as the ratio of the time-integrated radiative forcing from the instantaneous release of 1 kg of a trace substance relative to that of 1 kg of a reference gas:

${\mathit {GWP}}\left(x\right)={\frac {a_{x}}{a_{r}}}{\frac {\int _{0}^{\mathit {TH}}[x](t)\,dt}{\int _{0}^{\mathit {TH}}[r](t)\,dt}}$ where TH is the time horizon over which the calculation is considered; a_xis the radiative efficiency due to a unit increase in atmospheric abundance of the substance (i.e., Wm⁻²kg⁻¹) and [x](t) is the time-dependent decay in abundance of the substance following an instantaneous release of it at time t=0. The denominator contains the corresponding quantities for the reference gas (i.e.CO₂). The radiative efficiencies a_xand a_rare not necessarily constant over time. While the absorption of infrared radiation by many greenhouse gases varies linearly with their abundance, a few important ones display non-linear behaviour for current and likely future abundances (e.g., CO₂,CH₄,and N₂O). For those gases, the relative radiative forcing will depend upon abundance and hence upon the future scenario adopted.

Since all GWP calculations are a comparison to CO₂which is non-linear, all GWP values are affected. Assuming otherwise as is done above will lead to lower GWPs for other gases than a more detailed approach would. Clarifying this, while increasing CO₂has less and less effect on radiative absorption as ppm concentrations rise, more powerful greenhouse gases like methane and nitrous oxide have different thermal absorption frequencies to CO₂that are not filled up (saturated) as much as CO₂,so rising ppms of these gases are far more significant.

Applications

Carbon dioxide equivalent

Carbon dioxide equivalent (CO₂e or CO₂eq or CO₂-e) of a quantity of gas is calculated from its GWP. For any gas, it is the mass of CO₂which would warm the earth as much as the mass of that gas.^[33]Thus it provides a common scale for measuring the climate effects of different gases. It is calculated as GWP multiplied by mass of the other gas. For example, if a gas has GWP of 100, two tonnes of the gas have CO₂e of 200 tonnes, and 9 tonnes of the gas has CO₂e of 900 tonnes.

On a global scale, the warming effects of one or more greenhouse gases in the atmosphere can also be expressed as an equivalent atmospheric concentration of CO₂.CO₂e can then be the atmospheric concentration of CO₂which would warm the earth as much as a particular concentration of some other gas or of all gases and aerosols in the atmosphere. For example, CO₂e of 500 parts per million would reflect a mix of atmospheric gases which warm the earth as much as 500 parts per million of CO₂would warm it.^[34]^[35]Calculation of the equivalent atmospheric concentration of CO₂of an atmospheric greenhouse gas or aerosol is more complex and involves the atmospheric concentrations of those gases, their GWPs, and the ratios of their molar masses to the molar mass of CO₂.

CO₂e calculations depend on the time-scale chosen, typically 100 years or 20 years,^[36]^[37]since gases decay in the atmosphere or are absorbed naturally, at different rates.

The followingunitsare commonly used:

By the UN climate change panel (IPCC): billion metric tonnes = n×10⁹tonnesof CO₂equivalent (GtCO₂eq)^[38]
In industry: million metric tonnes of carbon dioxide equivalents (MMTCDE)^[39]and MMT CO₂eq.^[22]
For vehicles: grams of carbon dioxide equivalent per mile (gCO₂e/mile) or per kilometer (gCO₂e/km)^[40]^[41]

For example, the table above shows GWP for methane over 20 years at 86 and nitrous oxide at 289, so emissions of 1 million tonnes of methane or nitrous oxide are equivalent to emissions of 86 or 289 million tonnes of carbon dioxide, respectively.

Use in Kyoto Protocol and for reporting to UNFCCC

Under theKyoto Protocol,in 1997 the Conference of the Parties standardized international reporting, by deciding (see decision number 2/CP.3) that the values of GWP calculated for theIPCC Second Assessment Reportwere to be used for converting the various greenhouse gas emissions into comparable CO₂equivalents.^[42]^[43]

After some intermediate updates, in 2013 this standard was updated by the Warsaw meeting of theUN Framework Convention on Climate Change(UNFCCC, decision number 24/CP.19) to require using a new set of 100-year GWP values. They published these values in Annex III, and they took them from theIPCC Fourth Assessment Report,which had been published in 2007.^[21]Those 2007 estimates are still used for international comparisons through 2020,^[22]although the latest research on warming effects has found other values, as shown in the tables above.

Though recent reports reflect more scientific accuracy, countries and companies continue to use theIPCC Second Assessment Report(SAR)^[16]and IPCC Fourth Assessment Report values for reasons of comparison in their emission reports. TheIPCC Fifth Assessment Reporthas skipped the 500-year values but introduced GWP estimations including the climate-carbon feedback (f) with a large amount of uncertainty.^[13]

Other metrics to compare greenhouse gases

TheGlobal Temperature change Potential(GTP) is another way to compare gases. While GWP estimates infrared thermal radiation absorbed, GTP estimates the resulting rise in average surface temperature of the world, over the next 20, 50 or 100 years, caused by a greenhouse gas, relative to the temperature rise which the same mass of CO₂would cause.^[13]Calculation of GTP requires modelling how the world, especially the oceans, will absorb heat.^[24]GTP is published in the same IPCC tables with GWP.^[13]

Another metric called GWP* (pronounced "GWP star"^[44]) has been proposed to take better account of short-lived climate pollutants (SLCPs) such as methane. A permanent increase in the rate of emission of an SLCP has a similar effect to that of a one-time emission of an amount of carbon dioxide, because both raise the radiative forcing permanently or (in the case of carbon dioxide) practically permanently (since the CO₂stays in the air for a long time). GWP* therefore assigns anincreasein emission rate of an SLCP a supposedly equivalent amount (tonnes) of CO₂.^[45]However GWP* has been criticised both for its suitability as a metric and for inherent design features which can perpetuate injustices and inequity. Developing countries whose emissions of SLCPs are increasing are "penalized", while developed countries such as Australia or New Zealand which have steady emissions of SLCPs are not penalized in this way, though they may be penalized for their emissions of CO₂.^[46]^[47]^[44]

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^^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^tIPCC AR5 WG1 Ch8 2013,pp. 714, 731.
^This is so, because of the reaction formula: CH₄+ 2O₂→ CO₂+ 2 H₂O. 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⁻¹) will yield one molecule of carbon dioxide (molar mass = 44.01 g mol⁻¹). This gives a mass ratio of 2.74. (44.01/16.04 ≈ 2.74).
^^a ^b ^cWarwick, Nicola; Griffiths, Paul; Keeble, James; Archibald, Alexander; John, Pile (2022-04-08).Atmospheric implications of increased hydrogen use(Report). UK Department for Business, Energy & Industrial Strategy (BEIS).
^^a ^b ^c ^d ^e ^f ^gIPCC SAR WG1 Ch2 1995,p. 121.
^^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^pIPCC AR4 WG1 Ch2 2007,p. 212.
^Alvarez (2018)."Assessment of methane emissions from the U.S. oil and gas supply chain".Science.361(6398): 186–188.Bibcode:2018Sci...361..186A.doi:10.1126/science.aar7204.PMC6223263.PMID 29930092.
^Etminan, M.; Myhre, G.; Highwood, E. J.; Shine, K. P. (28 December 2016)."Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing".Geophysical Research Letters.43(24).Bibcode:2016GeoRL..4312614E.doi:10.1002/2016GL071930.
^^a ^bMorton, Adam (26 August 2020)."Methane released in gas production means Australia's emissions may be 10% higher than reported".The Guardian.
^^a ^b"Report of the Conference of the Parties on its 19th Session"(PDF).UNFCCC.2014-01-31.Archived(PDF)from the original on 2014-07-13.Retrieved2020-07-01.
^^a ^b ^c"Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2018, p. ES-3"(PDF).US Environmental Protection Agency.2020-04-13.Archived(PDF)from the original on 2020-04-14.Retrieved2020-07-01.
^Regulation (EU) No 517/2014 of the European Parliament and of the Council of 16 April 2014 on fluorinated greenhouse gasesAnnex IV.
^^a ^b"Understanding Global Warming Potentials".United States Environmental Protection Agency.12 January 2016.Retrieved2021-03-02.
^Abernethy, Sam; Jackson, Robert B (February 2022). "Global temperature goals should determine the time horizons for greenhouse gas emission metrics".Environmental Research Letters.17(2): 024019.arXiv:2104.05506.Bibcode:2022ERL....17b4019A.doi:10.1088/1748-9326/ac4940.S2CID 233209965.
^Sherwood, Steven C.; Dixit, Vishal; Salomez, Chryséis (2018)."The global warming potential of near-surface emitted water vapour".Environmental Research Letters.13(10): 104006.Bibcode:2018ERL....13j4006S.doi:10.1088/1748-9326/aae018.hdl:1959.4/unsworks_57193.S2CID 158806342.
^"The NOAA Annual Greenhouse Gas Index (AGGI)".NOAA.gov.National Oceanic and Atmospheric Administration (NOAA). Spring 2023.Archivedfrom the original on 24 May 2023.
^"Annual Greenhouse Gas Index".U.S. Global Change Research Program.Archivedfrom the original on 21 April 2021.Retrieved5 September2020.
^Butler J. and Montzka S. (2020)."The NOAA Annual Greenhouse Gas Index (AGGI)".NOAAGlobal Monitoring Laboratory/Earth System Research Laboratories.Archivedfrom the original on 22 September 2013.Retrieved5 September2020.
^Matthew Elrod, "Greenhouse Warming Potential Model."Based onElrod, M. J. (1999). "Greenhouse Warming Potentials from the Infrared Spectroscopy of Atmospheric Gases".Journal of Chemical Education.76(12): 1702.Bibcode:1999JChEd..76.1702E.doi:10.1021/ed076p1702.
^ "Glossary: Global warming potential (GWP)".U.S. Energy Information Administration.Retrieved2011-04-26.An index used to compare the relative radiative forcing of different gases without directly calculating the changes in atmospheric concentrations. GWPs are calculated as the ratio of the radiative forcing that would result from the emission of one kilogram of a greenhouse gas to that from the emission of one kilogram of carbon dioxide over a fixed period of time, such as 100 years.
^"Climate Change 2001: The Scientific Basis".grida.no.Archived fromthe originalon 31 January 2016.Retrieved11 January2022.
^"CO2e".www3.epa.gov.Retrieved2020-06-27.
^"Atmospheric greenhouse gas concentrations – Rationale".European Environment Agency.2020-02-25.Retrieved2020-06-28.
^Gohar, L. K.; Shine, K. P. (November 2007)."Equivalent CO₂and its use in understanding the climate effects of increased greenhouse gas concentrations ".Weather.62(11): 307–311.Bibcode:2007Wthr...62..307G.doi:10.1002/wea.103.
^Wedderburn-Bisshop, Gerard; Longmire, Andrew; Rickards, Lauren (2015). "Neglected Transformational Responses: Implications of Excluding Short Lived Emissions and Near Term Projections in Greenhouse Gas Accounting".The International Journal of Climate Change: Impacts and Responses.7(3): 11–27.doi:10.18848/1835-7156/CGP/v07i03/37242.ProQuest 2794017083.
^Ocko, Ilissa B.; Hamburg, Steven P.; Jacob, Daniel J.; Keith, David W.; Keohane, Nathaniel O.; Oppenheimer, Michael; Roy-Mayhew, Joseph D.; Schrag, Daniel P.; Pacala, Stephen W. (5 May 2017). "Unmask temporal trade-offs in climate policy debates".Science.356(6337): 492–493.Bibcode:2017Sci...356..492O.doi:10.1126/science.aaj2350.PMID 28473552.S2CID 206653952.
^Denison, Steve; Forster, Piers M; Smith, Christopher J (December 2019)."Guidance on emissions metrics for nationally determined contributions under the Paris Agreement".Environmental Research Letters.14(12): 124002.Bibcode:2019ERL....14l4002D.doi:10.1088/1748-9326/ab4df4.
^"Glossary:Carbon dioxide equivalent – Statistics Explained".ec.europa.eu.Retrieved2020-06-28.
^"How Clean is Your Electric Vehicle?".Union of Concerned Scientists.Retrieved2020-07-02.
^Whitehead, Jake (2019-09-07)."The Truth About Electric Vehicle Emissions".realclearscience.Retrieved2020-07-02.
^ Conference of the Parties (25 March 1998). "Methodological issues related to the Kyoto Protocol".Report of the Conference of the Parties on its third session, held at Kyoto from 1 to 11 December 1997 Addendum Part Two: Action taken by the Conference of the Parties at its third session(PDF).UNFCCC.Archived(PDF)from the original on 2000-08-23.Retrieved17 January2011.
^Godal, Odd; Fuglestvedt, Jan (2002). "Testing 100-year global warming potentials: Impacts on compliance costs and abatement profile".Climatic Change.52(1/2): 93–127.doi:10.1023/A:1013086803762.S2CID 150488348.ProQuest 198550594.
^^a ^bRogelj, Joeri; Schleussner, Carl-Friedrich (1 June 2021)."Reply to Comment on 'Unintentional unfairness when applying new greenhouse gas emissions metrics at country level'".Environmental Research Letters.16(6): 068002.Bibcode:2021ERL....16f8002R.doi:10.1088/1748-9326/ac02ec.
^Lynch, John; Cain, Michelle; Pierrehumbert, Raymond; Allen, Myles (April 2020)."Demonstrating GWP*: a means of reporting warming-equivalent emissions that captures the contrasting impacts of short- and long-lived climate pollutants".Environmental Research Letters.15(4): 044023.Bibcode:2020ERL....15d4023L.doi:10.1088/1748-9326/ab6d7e.PMC7212016.PMID 32395177.
^Meinshausen, Malte; Nicholls, Zebedee (1 April 2022)."GWP*is a model, not a metric".Environmental Research Letters.17(4): 041002.Bibcode:2022ERL....17d1002M.doi:10.1088/1748-9326/ac5930.
^Rogelj, Joeri; Schleussner, Carl-Friedrich (1 November 2019). "Unintentional unfairness when applying new greenhouse gas emissions metrics at country level".Environmental Research Letters.14(11): 114039.Bibcode:2019ERL....14k4039R.doi:10.1088/1748-9326/ab4928.hdl:10044/1/77353.S2CID 250668916.

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[:2-1] IPCC, 2021: 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.)]. InClimate 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.

[:0-2] 7.SM.6 Tables of greenhouse gas lifetimes, radiative efficiencies and metrics(PDF),IPCC,2021, p. 7SM-24.

[nrcrf-3] National Research Council (2005).Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties.The National Academic Press.doi:10.17226/11175.ISBN 978-0-309-09506-8.

[4] Drew, Shindell (2013)."Climate Change 2013: The Physical Science Basis – Working Group 1 contribution to the IPCC Fifth Assessment Report: Radiative Forcing in the AR5"(PDF).Department of Environmental Sciences, School of Environmental and Biological Sciences.envsci.rutgers.edu.Rutgers University.Fifth Assessment Report(AR5).Archived(PDF)from the original on 4 March 2016.Retrieved15 September2016.

[:5-5] Amendment to the Montreal Protocol on Substances that Deplete the Ozone Layer(the "Montreal Protocol" ), adopted at Kigali on October 15, 2016, by the Twenty-Eighth Meeting of the Parties to the Montreal Protocol (the "Kigali Amendment" ).

[6] "Understanding Global Warming Potentials".US EPA, Greenhouse Gas Emissions.August 8, 2024.RetrievedAugust 26,2024.{{cite web}}:CS1 maint: url-status (link)

[7] "Global warming potential of greenhouse gases relative to CO2".Our World in Data.Retrieved2023-12-18.

[:02-8] IPCC, 2021: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.)]. InClimate 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.

[ar6_WG1_Ch_7-9] ^^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^abForster, 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:Chapter 7: The Earth's Energy Budget, Climate Feedbacks, and Climate Sensitivity.Inhttps:// 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.

[10] Yang, Rui; Yuan, Lin- gian g; Wang, Ru; He, Zhi-xian; Lei, Lin; Ma, Yan-chen (2022)."Analyzing the mechanism of nitrous oxide production in aerobic phase of anoxic/aerobic sequential batch reactor from the perspective of key enzymes".Environmental Science and Pollution Research.29(26): 39877–39887.doi:10.1007/s11356-022-18800-3.ISSN 0944-1344.

[TableOfWarmingPotentials5-11] "Appendix 8.A"(PDF).Intergovernmental Panel on Climate Change Fifth Assessment Report.p. 731.Archived(PDF)from the original on 13 October 2017.Retrieved6 November2017.

[TableOfWarmingPotentials-12] "Table 2.14"(PDF).IPCC Fourth Assessment Report.p. 212.Archived(PDF)from the original on 15 December 2007.Retrieved16 December2008.

[ar5-13] ^^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^tIPCC AR5 WG1 Ch8 2013,pp. 714, 731.

[14] This is so, because of the reaction formula: CH₄+ 2O₂→ CO₂+ 2 H₂O. 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⁻¹) will yield one molecule of carbon dioxide (molar mass = 44.01 g mol⁻¹). This gives a mass ratio of 2.74. (44.01/16.04 ≈ 2.74).

[:3-15] Warwick, Nicola; Griffiths, Paul; Keeble, James; Archibald, Alexander; John, Pile (2022-04-08).Atmospheric implications of increased hydrogen use(Report). UK Department for Business, Energy & Industrial Strategy (BEIS).

[sar-16] ^^a ^b ^c ^d ^e ^f ^gIPCC SAR WG1 Ch2 1995,p. 121.

[ar4-17] ^^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^pIPCC AR4 WG1 Ch2 2007,p. 212.

[18] Alvarez (2018)."Assessment of methane emissions from the U.S. oil and gas supply chain".Science.361(6398): 186–188.Bibcode:2018Sci...361..186A.doi:10.1126/science.aar7204.PMC6223263.PMID 29930092.

[19] Etminan, M.; Myhre, G.; Highwood, E. J.; Shine, K. P. (28 December 2016)."Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing".Geophysical Research Letters.43(24).Bibcode:2016GeoRL..4312614E.doi:10.1002/2016GL071930.

[:4-20] Morton, Adam (26 August 2020)."Methane released in gas production means Australia's emissions may be 10% higher than reported".The Guardian.

[unfccc19-21] "Report of the Conference of the Parties on its 19th Session"(PDF).UNFCCC.2014-01-31.Archived(PDF)from the original on 2014-07-13.Retrieved2020-07-01.

[epa20-22] "Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2018, p. ES-3"(PDF).US Environmental Protection Agency.2020-04-13.Archived(PDF)from the original on 2020-04-14.Retrieved2020-07-01.

[23] Regulation (EU) No 517/2014 of the European Parliament and of the Council of 16 April 2014 on fluorinated greenhouse gasesAnnex IV.

[:1-24] "Understanding Global Warming Potentials".United States Environmental Protection Agency.12 January 2016.Retrieved2021-03-02.

[25] Abernethy, Sam; Jackson, Robert B (February 2022). "Global temperature goals should determine the time horizons for greenhouse gas emission metrics".Environmental Research Letters.17(2): 024019.arXiv:2104.05506.Bibcode:2022ERL....17b4019A.doi:10.1088/1748-9326/ac4940.S2CID 233209965.

[26] Sherwood, Steven C.; Dixit, Vishal; Salomez, Chryséis (2018)."The global warming potential of near-surface emitted water vapour".Environmental Research Letters.13(10): 104006.Bibcode:2018ERL....13j4006S.doi:10.1088/1748-9326/aae018.hdl:1959.4/unsworks_57193.S2CID 158806342.

[NOAA_AGGI_2022-27] "The NOAA Annual Greenhouse Gas Index (AGGI)".NOAA.gov.National Oceanic and Atmospheric Administration (NOAA). Spring 2023.Archivedfrom the original on 24 May 2023.

[28] "Annual Greenhouse Gas Index".U.S. Global Change Research Program.Archivedfrom the original on 21 April 2021.Retrieved5 September2020.

[butmon-29] Butler J. and Montzka S. (2020)."The NOAA Annual Greenhouse Gas Index (AGGI)".NOAAGlobal Monitoring Laboratory/Earth System Research Laboratories.Archivedfrom the original on 22 September 2013.Retrieved5 September2020.

[30] Matthew Elrod, "Greenhouse Warming Potential Model."Based onElrod, M. J. (1999). "Greenhouse Warming Potentials from the Infrared Spectroscopy of Atmospheric Gases".Journal of Chemical Education.76(12): 1702.Bibcode:1999JChEd..76.1702E.doi:10.1021/ed076p1702.

[31] "Glossary: Global warming potential (GWP)".U.S. Energy Information Administration.Retrieved2011-04-26.An index used to compare the relative radiative forcing of different gases without directly calculating the changes in atmospheric concentrations. GWPs are calculated as the ratio of the radiative forcing that would result from the emission of one kilogram of a greenhouse gas to that from the emission of one kilogram of carbon dioxide over a fixed period of time, such as 100 years.

[32] "Climate Change 2001: The Scientific Basis".grida.no.Archived fromthe originalon 31 January 2016.Retrieved11 January2022.

[epadef-33] "CO2e".www3.epa.gov.Retrieved2020-06-27.

[eea-34] "Atmospheric greenhouse gas concentrations – Rationale".European Environment Agency.2020-02-25.Retrieved2020-06-28.

[rmets-35] Gohar, L. K.; Shine, K. P. (November 2007)."Equivalent CO₂and its use in understanding the climate effects of increased greenhouse gas concentrations ".Weather.62(11): 307–311.Bibcode:2007Wthr...62..307G.doi:10.1002/wea.103.

[Wedderburn-Bisshop_et_al_2015-36] Wedderburn-Bisshop, Gerard; Longmire, Andrew; Rickards, Lauren (2015). "Neglected Transformational Responses: Implications of Excluding Short Lived Emissions and Near Term Projections in Greenhouse Gas Accounting".The International Journal of Climate Change: Impacts and Responses.7(3): 11–27.doi:10.18848/1835-7156/CGP/v07i03/37242.ProQuest 2794017083.

[OckoHamburg2017-37] Ocko, Ilissa B.; Hamburg, Steven P.; Jacob, Daniel J.; Keith, David W.; Keohane, Nathaniel O.; Oppenheimer, Michael; Roy-Mayhew, Joseph D.; Schrag, Daniel P.; Pacala, Stephen W. (5 May 2017). "Unmask temporal trade-offs in climate policy debates".Science.356(6337): 492–493.Bibcode:2017Sci...356..492O.doi:10.1126/science.aaj2350.PMID 28473552.S2CID 206653952.

[38] Denison, Steve; Forster, Piers M; Smith, Christopher J (December 2019)."Guidance on emissions metrics for nationally determined contributions under the Paris Agreement".Environmental Research Letters.14(12): 124002.Bibcode:2019ERL....14l4002D.doi:10.1088/1748-9326/ab4df4.

[39] "Glossary:Carbon dioxide equivalent – Statistics Explained".ec.europa.eu.Retrieved2020-06-28.

[ucs-ev-40] "How Clean is Your Electric Vehicle?".Union of Concerned Scientists.Retrieved2020-07-02.

[rcs-41] Whitehead, Jake (2019-09-07)."The Truth About Electric Vehicle Emissions".realclearscience.Retrieved2020-07-02.

[42] Conference of the Parties (25 March 1998). "Methodological issues related to the Kyoto Protocol".Report of the Conference of the Parties on its third session, held at Kyoto from 1 to 11 December 1997 Addendum Part Two: Action taken by the Conference of the Parties at its third session(PDF).UNFCCC.Archived(PDF)from the original on 2000-08-23.Retrieved17 January2011.

[43] Godal, Odd; Fuglestvedt, Jan (2002). "Testing 100-year global warming potentials: Impacts on compliance costs and abatement profile".Climatic Change.52(1/2): 93–127.doi:10.1023/A:1013086803762.S2CID 150488348.ProQuest 198550594.

[Reply-44] Rogelj, Joeri; Schleussner, Carl-Friedrich (1 June 2021)."Reply to Comment on 'Unintentional unfairness when applying new greenhouse gas emissions metrics at country level'".Environmental Research Letters.16(6): 068002.Bibcode:2021ERL....16f8002R.doi:10.1088/1748-9326/ac02ec.

[45] Lynch, John; Cain, Michelle; Pierrehumbert, Raymond; Allen, Myles (April 2020)."Demonstrating GWP*: a means of reporting warming-equivalent emissions that captures the contrasting impacts of short- and long-lived climate pollutants".Environmental Research Letters.15(4): 044023.Bibcode:2020ERL....15d4023L.doi:10.1088/1748-9326/ab6d7e.PMC7212016.PMID 32395177.

[46] Meinshausen, Malte; Nicholls, Zebedee (1 April 2022)."GWP*is a model, not a metric".Environmental Research Letters.17(4): 041002.Bibcode:2022ERL....17d1002M.doi:10.1088/1748-9326/ac5930.

[47] Rogelj, Joeri; Schleussner, Carl-Friedrich (1 November 2019). "Unintentional unfairness when applying new greenhouse gas emissions metrics at country level".Environmental Research Letters.14(11): 114039.Bibcode:2019ERL....14k4039R.doi:10.1088/1748-9326/ab4928.hdl:10044/1/77353.S2CID 250668916.

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