Greenhouse gas conversion factors (Resource)

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What are conversion factors?

Global warming potential (GWP) conversion factors convert non-CO2 greenhouse gases (GHGs), e.g., Methane (CH4) or Nitrous oxide (N2O), into the equivalent measure of Carbon dioxide (CO2) in terms of the relative global warming potential (GWP), yielding CO2-equivalent (CO2e), the common unit for all greenhouse gases. Using conversion factors to convert GHGs is similar to the way currency exchange rates are used to covert value between currencies. However, GWP conversion factors do not exhibit short-term or long-term "market volatility" due to socioeconomic factors or general market sentiment (confidence), as is the case with currencies. Rather, the global warming potential (GWP) of all non-CO2 greenhouse gases, relative to CO2, decreases (and in a few cases, increases, e.g., for the Fluorinated Species, including PFCs) over longer timelines (e.g., 20-year, 100-year or 500-year). It's worth reiterating: the GWP of nearly all greenhouse gases decreases over longer timelines. These changes in GWP, by greenhouse gas, are determined using best-available scientific knowledge and evidence. These changes are like fixed rates of depreciation or appreciation over specific timelines. In short, the global warming potential of all greenhouse gases is known to a high-enough-degree of certainty for the purpose of making well-informed calculations, estimates and decisions therefrom.

Guidance on WikiCarbon

Editors compiling on WikiCarbon, where possible, should (i) use 100-year Global Warming Potential ("GWP100") conversion factors, specifically, (ii) from the Fifth Assessment Report (AR5) of the United Nations Intergovernmental Panel on Climate Change (IPCC, 2013).[1] This facilitates robust cross-comparability of any and all Final calculations (GHG inventories, aka "Carbon" inventories) from Product Carbon Footprint (PCF) Assessments and/or GHG Life-Cycle Assessment (LCA) reports summarized on this WikiCarbon. Further, using GWP100 conversion factors satisfies conformance requirements associated with internationally recognized product life cycle accounting and reporting standards. Note that GWP conversion factors have been and will continue being revised, every five years, approximately, with each Assessment Report (AR) from the IPCC.

In many cases, it will not be feasible to use the GWP100 (IPCC, 2013) conversion factors, as many historical assessments compiled on WikiCarbon will rely on dated PCF assessments and/or LCA reports -- which, despite almost always using GWP100 conversion factors, will have relied on older datasets, i.e., GWP conversion factors from the Fourth Assessment Report (AR4) (IPCC, 2007), or the Second Assessment Report (SAR) (IPCC, 1995). In several instances, identical GHG Inventories (e.g., quantities of greenhouse gases) will exhibit little variation when converted to a CO2-equivalent basis, regardless of the GWP conversion factor dataset in use; largely, because CO2 will be the only or most prevalent GHG quantified. Carbon dioxide (CO2) accounts for the largest share of global, human-caused greenhouse gases on a GWP-weighted basis, and the conversion factor for CO2 is always one; therefore, for many GHG inventories, on a GWP-weighted basis may exhibit little change regardless of the set of GWP conversion factors being used to convert to the common unit, CO2e. If a GHG Inventory only includes CO2, then there will be no difference, regardless of which datasets is used, i.e., (IPCC, 2013), (IPCC, 2007), or (IPCC, 1995), because the GWP conversion factor for CO2 is equal to one (i.e., one unit CO2e per unit CO2) in all datasets. However, if the GHG Inventory includes other gases, in addition to CO2, e.g., Methane (CH4) and Nitrous oxide (N2O), then the GHG inventory and subsequent GWP-weighted results for products, using the common unit CO2e, may differ significantly, e.g., for livestock and/or agriculture which cause a significant portion of global, human-caused CH4 and N2O emissions.

Conversion factors for the Big Three

The 100-year and 20-year GWP conversion factors below originate from Appendix 8.A: Lifetimes, Radiative Efficiencies and Metric Values (IPCC, 2013).[1] The 500-year GWP conversion factors below originate from Table 2.14 in Chapter 2, Changes in Atmospheric Constituents and Radiative Forcing, from (IPCC, 2007). For more detail on Other Trace Gases (e.g., CFCs, HCFCs, HFCs, PFCs, and SF6), refer to the following article, What Are Greenhouse Gases?.[2]

Table 1a: GWP Conversion factors for the "Big Three"

The "Big Three" greenhouse gases account for approximately 98% of all greenhouse gases on a 100-year GWP-weighted basis. Carbon dioxide (CO2) accounts for 75% on a 100-year GWP-weighted basis. Refer to the Big Three for an outline of these three most prevalent GHGs (i.e., CO2, CH4, and N2O), including citations for the aforementioned statistics. Note that all 500-year GWP conversion factors originate from (IPCC, 2007) and the 20-year and 100-year GWP conversion factors from (IPCC, 2013).[3]

Table 1a. GWP Conversion Factors for the "Big Three"
Greenhouse Gas Lifetime

(years)[1]

20-year

GWPs[1]

100-year

GWPs[1][4]

500-year

GWPs[3]

Carbon dioxide (CO2) n/a 1.0 1.0 1.0
Methane (CH4) 12.4 84.0 28.0 7.6[5]
Fossil Methane (CH4) 12.4 85.0 30.0 n/a[6]
Nitrous Oxide (N2O) 121.0 264.0 265.0 153.0[7]

Table 1b: Depreciation of the GWP conversion factors of the Big Three

Regarding the "n/a" lifetime (years) for CO2: the lifetime of CO2 varies significantly as is not listed in either (IPCC, 2007) nor (IPCC, 2013), like it is for other greenhouse gases. That said, as per (Archer, et al., 2009), approximately "20-40% [of CO2 emissions from fossil fuel combustion, which accounts for the largest share of human-caused CO2 emissions]... remain[s] in the atmosphere awaiting slower chemical reactions," on a timescale of thousands of years, and this fraction, "is abundant enough to continue to have a substantial impact on climate for thousands of years."[8] The lifetime of CO2 is factored into the GWP of all other greenhouse gases.

Table 1b. "Big Three" % of Base
Greenhouse Gas 20-year

GWPs[1]

100-year

GWPs[1][4]

500-year

GWPs[3]

Carbon dioxide (CO2) 100% 100% 100%
Methane (CH4) 100% 33% 9%
Fossil Methane (CH4) 100% 35% 9%
Nitrous Oxide (N2O) 100% 100% 58%

Conversion factors for all Other Trace Gases, Group Median

While Other Trace Gases, on average, have significantly global warming potential (GWP) than the Big Three greenhouse gases on a 20-year timescale, their GWP depreciates significantly, over time, relative to the GWP of Carbon dioxide (CO2). Other Trace Gases, in aggregate, account for approximately 3% of total, global greenhouse gases on a 100-year GWP-weighted basis, and would account for less on a 500-year basis, as would Methane and Nitrous oxide.

Table 2. Median GWP Conversion factors for Other Trace Gases

The following are the median GWP conversion factors of trace gases, by group, for each timeframe. Note that only the 20-year and 100-year group, median GWP figures are comparable, as they include full datasets, i.e., all Other Trace Gases, of which there are 203. The 500-year GWP conversion factors of trace gases, by group, for each timeframe, includes GWP conversion factors for less than half as many trace gases, and may not reflect best-available science as that median figure, i.e., for the 500-year timescale.

The median GWP conversion factor of nearly all Other Trace Gases, by group, decreases by about 73% when moving from the 20-year to the 100-year timescale. This is the case for the median GWP of five out of seven groups, i.e., (i) HCFCs, (ii) HFCs, (iii) Chlorocarbons and Hydrochlorocarbons, (iv) Bromocarbons, Hydrobromocarbons and Halons, and (v) Halogenated Alcohols and Ethers. The median GWP conversion factor for the group, CFCs, increases when moving from the 20-year to the 100-year timescale; the decreases on a 500-year timescale may not reflect best-available science as that median figure, i.e., for the 500-year timescale, originates from (IPCC, 2007), while both the 20-year and 100-year median GWP figures originate from (IPCC, 2013).

The median GWP of all Other Trace Gases is 1,230 on a 20-year timescale and 338 on a 100-year timescale, which reflects a 73% decrease. For both the 20-year and 100p-year timescales, of all Other Trace Gases, the greenhouse gas with the median GWP happens to be HCFC-132c, which is one of the thirteen Hydrochlorofluorocarbons (HCFCs) (IPCC, 2013). HCFC-132c does not have a 500-year GWP conversion factor listed in (IPCC, 2007), so the median GWP of all Other Trace Gases on the 500-year timescale corresponds with HFE-347mcc3 (HFE-7000), which is classified under the last group, Halogenated Alcohol and Ethers.

Table 2. Median GWP Conversion factors for Other Trace Gases[9][10]
Group of Other Trace Gases No. gases

(20-/100-year datasets)[11]

No. gases

(500-year dataset)[11]

Lifetime

in years[1]

Median

20-year GWPs

[1][11] Median

100-year

GWPs

[1][11]

Median

500-year GWPs

[3][11]

Median

Chlorofluorocarbons (CFCs) 6 6 145 7,305 8,130 6,965
Hydrochlorofluorocarbons (HCFCs) 13 8 4 1,230 338 183
Hydrofluorocarbons (HFCs) 39 25 3 863 235 1
Chlorocarbons and Hydrochlorocarbons 6 5 1 53 14 4
Bromocarbons, Hydrobromocarbons and Halons 10 5 3 761 208 503
Fully Fluorinated Species (PFCs, including SF6) 23 11 2,000 5,830 7,620 13,300
Halogenated Alcohols and Ethers 106 31 2 842 229 5
All Other Trace Gases 203 91 3 1,230 338 175

Table 3: Depreciation of the Simple, Median GWP of Other Trace Gases by Group

The % figures below show the median GWP conversion factor of each timescale, by group, relative to (as a % of) a group's, median 20-year GWP conversion factor. Note that only the 20-year and 100-year group, median GWP figures are comparable, as they include full datasets, i.e., all Other Trace Gases, of which there are 203. The 500-year GWP conversion factors of trace gases, by group, for each timeframe, includes GWP conversion factors for less than half as many trace gases, and may not reflect best-available science as that median figure, i.e., for the 500-year timescale.

That said, these % figures are like the inverse of depreciation. For example, for HCFCs, the group, median GWP depreciates by 73% when moving from the 20-year to 100-year timeframe; thus, the group, median 100-year GWP conversion factor is 27% that of the group, median 20-year GWP conversion factor ("BASE"). This is similar to Method B (in Table 6), below, however, the methodology in Table 3 below uses group median GWP figures, and not group average GWP figures like in Table 6.

This methodology may make the figures in this table misleading, depending on how and for what they are used. These median figures should not be used for calculations; they are provided here for informative purposes. It's worth keeping in mind that statistical measures are only supposed to useful, and that it's prudent to be wary of any and all statistical measures (Refer to the quote by George Box in Principles & Rules). The use of median and averages may make the figures in this table misleading, depending on how and for what they are used. These percentage figures should not be used in any calculations; they are provided here for informative purposes.

Table 3. % of Base, of Simple-Median values by Group[1]
Group of Other Trace Gases 20-year GWP

Median,

% of BASE

100-year GWP

Median,

% of BASE

500-year GWP

Median,

% of BASE

Chlorofluorocarbons (CFCs) 100% 111% 95%
Hydrochlorofluorocarbons (HCFCs) 100% 27% 15%
Hydrofluorocarbons (HFCs) 100% 27% 0%
Chlorocarbons and Hydrochlorocarbons 100% 27% 8%
Bromocarbons, Hydrobromocarbons and Halons 100% 27% 66%
Fully Fluorinated Species (PFCs, including SF6) 100% 131% 228%
Halogenated Alcohols and Ethers 100% 27% 1%
All Other Trace Gases 100% 27% 14%

Conversion factors for all Other Trace Gases, Group Average

Table 4: Average GWP Conversion factors for Other Trace Gases

This table provides summaries all other greenhouse gases, apart from the "Big Three," of which there are two hundred and three (203) as per (IPCC, 2013). Given that there are so many Other Trace Gases, they are grouped. by timeframe and summarized with each group's respective range of GWPs (low to high) and group simple average GWP.

This methodology may make the figures in this table misleading, depending on how and for what they are used. These averages should not be used for calculations; they are provided here for informative purposes.

Note: (i) some GWP conversion factors have a value of less than one (<1) which, for the purpose of calculating each group's simple average, are given a value of one; (ii) the 500-year dataset from (IPCC, 2007) contains GWP conversion factors for less than half has many gases as are featured in the 20-/100-year datasets from (IPCC, 2013); and (iii) the average are, as stated, simple averages, meaning that they are not weighted, i.e., they do not factor in which gases are more or less prevalent in a group which, undoubtedly, would generate different averages.

For example, the 500-year GWPs of three of the six CFCs, on average, are 44% that of the 100-year GWPs, while for the other three CFCs, on average, the 500-year GWPs are 116% that of the 100-year GWPs; and together, all six CFCs exhibit the a That said, because these Other Trace Gases are not nearly as prevalent as the "Big Three," simple averages, by deduction, may be sufficient and meaningful indication.

Table 4. Average GWP Conversion factors for Other Trace Gases[1]
Group of Other Trace Gases No. gases

(20-/100-year datasets)[11]

No. gases

(500-year dataset)[11]

Lifetime

in years, Range and (Average)[1][9]

20-year

GWPs, Range and (Average)[1][11][9]

100-year

GWPs, Range and (Average)[1][11][9]

500-year GWPs,

Range and (Average)[3][11]

Chlorofluorocarbons (CFCs) 6 6 45-1,020

(347)

5,860 to 10,900

(8,110)[11]

4,660 to 13,900

(8,473)[11]

1,620 to 16,400

(7,425)[11]

Hydrochlorofluorocarbons (HCFCs) 13 8 0 to 17

(5)

5 to 5,280

(1,664)[11]

1 to 1,980

(535)[11]

24 to 705

(238)[11]

Hydrofluorocarbons (HFCs) 39 25 0 to 242

(20)

1 to 10,800

(2,233)[11][10]

0 to 12,400

(1,344)[11][10]

0 to 12,200

(1,013)[11][10]

Chlorocarbons and Hydrochlorocarbons 6 5 0 to 26

(5)

3 to 3,480

(700)[11][10]

0 to 1,730

(321)[11][10]

0 to 435

(98)[11][10]

Bromocarbons, Hydrobromocarbons and Halons 10 5 0 to 65

(12)

4 to 7,800

(1,950)[11][10]

1 to 6,290

(1,052)[11][10]

0 to 2,760

(768)[11][10]

Fully Fluorinated Species (PFCs, including SF6) 23 11 0 to 50,000

(4,138)

0 to 17,500

(5,674)[11][10]

0 to 23,500

(7,317)[11][10]

0 to 32,600

(14,177)[11][10]

Halogenated Alcohols and Ethers 106 31 0 to 800

(15)

0 to 15,100

(2,512)[11][10]

0 to 12,400

(1,173)[11][10]

33 to 8,490

(639)[11][10]

All Other Trace Gases 203 91 0 to 50,000

(492)

0 to 17,500

(2,847)[11]

0 to 23,500

(2,046)[11]

0 to 23,500

(2,768)[11]

Table 5: Depreciation of the GWPs of Other Trace Gases by individual Gas, which is then Averaged (Method A)

The % figures in Table 5 below show the remaining (undepreciated) GWP of each gas, by group, relative to the 20-year GWP. These % figures are like the inverse of depreciation, e.g., for HCFCs, the group, average GWP depreciates by 72% when moving from the 20-year to 100-year timeframe GWPs and, thus, the group, average 100-year GWP conversion factor is 28% that of the group, average 20-year GWP conversion factor (the underlined figure being shown in the table below).

This methodology uses simple average each individual trace gas' GWP, by timeframe, relative to each trace gas' 20-year GWP conversion factor, i.e., treating the 20-year GWP conversion factors as Base), and calculates a simple average of these figures. This is different from Method B, which uses the averages, by group, as provided in Table 4 above, to determine the % base values. In short, Method A calculates the GWP relative to the 20-year base, by gas, and then takes the average, by group; whereas Method B takes the average GWP, by group, and then calculates the group, average GWP relative to the group, average 20-year GWP. Method A is, perhaps, the better method (of these two methods) to assess the relative GWP by group, by timeframe.

However, it's worth keeping in mind that averages are only supposed to useful, and that it's prudent to be wary of any and all statistical measures (Refer to the quote by George Box in Principles & Rules). The use of averages may make the figures in this table misleading, depending on how and for what they are used. These percentage figures should not be used in any calculations; they are provided here for informative purposes.

Table 5. Comp Method A: Simple-Average of individual gases % of BASE[1]
Group of Other Trace Gases 20-year GWP

Average,

% of BASE

100-year GWP

Average,

% of BASE

500-year GWP

Average,

% of BASE

Chlorofluorocarbons (CFCs) 100% 104% 91%
Hydrochlorofluorocarbons (HCFCs) 100% 28% 10%
Hydrofluorocarbons (HFCs) 100% 43% 31%
Chlorocarbons and Hydrochlorocarbons 100% 32% 9%
Bromocarbons, Hydrobromocarbons and Halons 100% 35% 21%
Fully Fluorinated Species (PFCs, including SF6) 100% 119% 179%
Halogenated Alcohols and Ethers 100% 33% 12%
All Other Trace Gases 100% 46% 49%

Table 6: Depreciation of the Simple, Average GWP of Other Trace Gases by Group (Method B)

The % figures in Table 6 below show the remaining (undepreciated) GWP of each group of gases, relative to the group, average 20-year GWP. These % figures are like the inverse of depreciation, e.g., for HCFCs, the group, average GWP depreciates by 72% moving from the 20-year to 100-year timeframe, thus the group, average 100-year GWP conversion factor is 28% that of the group, average 20-year GWP conversion factor ("BASE").

This table shows the group, average GWP conversion factor, for every timeframe, relative to (as a % of) the 20-year GWP conversion factors, i.e., treating the group, average 20-year GWP conversion factors as Base (100%). This methodology may make the figures in this table misleading, depending on how and for what they are used. These percentage figures should not be used in any calculations; they are provided here for informative purposes.

In short, Method A calculates the GWP relative to the 20-year base, by gas, and then takes the average, by group; whereas Method B takes the average GWP, by group, and then calculates the group, average GWP relative to the group, average 20-year GWP. Method A is, perhaps, the better method (of these two methods) to assess the relative GWP by group, by timeframe.

These % figures rely on the simple average of the available GWP conversion factors of Other Trace Gases, by group, by timeframe; and not the weighted-average of the GWP conversion factors of each group by timeframe. The simple average GWP conversion factors of Other Trace Gases, by group, apart from Fully Fluorinated Species, comprised of mostly Perfluorocarbons (PFCs), depreciates when moving from the 100-year to the 500-year timeframe. The simple average GWP conversion factors of Other Trace Gases, by group, apart from Chlorofluorocarbons (CFCs) and Fully Fluorinated Species (mostly PFCs), depreciations when moving from the 20-year timeframe to the 100-year timeframe.

For example, for HCFCs, the group, average 100-year GWP conversion factor of 535 is 32% that of the 20-year GWP of 1,664, which reflects a 68% decrease of the group average GWP conversion factor. The group, average 500-year GWP conversion factor drops to 238 which is 14% that of the group, average 20-year GWP conversion factor of 1,664. See Table 4 for all underlined figures in this example.

Table 6. Comp Method B: % of Base, Simple Group-Average[1]
Group of Other Trace Gases 20-year GWP

Average,

% of BASE

100-year GWP

Average,

% of BASE

500-year GWP

Average,

% of BASE

Chlorofluorocarbons (CFCs) 100% 104% 92%
Hydrochlorofluorocarbons (HCFCs) 100% 32% 14%
Hydrofluorocarbons (HFCs) 100% 60% 45%
Chlorocarbons and Hydrochlorocarbons 100% 46% 14%
Bromocarbons, Hydrobromocarbons and Halons 100% 54% 39%
Fully Fluorinated Species (PFCs, including SF6) 100% 129% 250%
Halogenated Alcohols and Ethers 100% 47% 25%
All Other Trace Gases 100% 72% 97%

What are GTP conversion factors?

In addition to GWP conversion factors, the IPCC provides another set called Global Temperature change Potential (GTP) conversion factors. The GWP relies on the radiative forcing (RF) of GHGs over a specific time-horizon, relative to the RF of CO2; and the GTP goes one step further by integrating a projected ratio of change in global mean surface temperature at a specific point in time in the future, relative to that of CO2. As stated, while there are "uncertainties related to both GWP and GTP," the "relative uncertainties are larger for GTP."[12] As such, the GWP conversion factors, and specifically, over a 100-year time-horizon, are used by all standards (WRI/WBCSD, BSI, and ISO). These factors have been and will continue being revised, every five years, with each new Assessment Report (AR) from the IPCC. As such it's important to use the most recent from AR5. [Note: Figures below have been pulled from Appendix 8.A: Lifetimes, Radiative Efficiencies and Metric Values.][1]

References

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 (IPCC, 2013): Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Kock, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakjima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifith Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
  2. Gillenwater, Michael. June 15, 2010. "What Are Greenhouse Gases?" GHG Management Institute, 2008-2019. Accessed: 2019/10/20; Archived: 2019/10/20. [1]
  3. 3.0 3.1 3.2 3.3 3.4 (IPCC, 2007): Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland, 2007: Changes in Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Millner (eds.)]. Cambridge University Press, United Kingdom and New York, NY, USA. Available electronically: <https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-chapter2-1.pdf>. Accessed: September 29, 2020.
  4. 4.0 4.1 Note: (IPCC, 2007) conversion factors were: 1, 25 (both types of methane), and 298, for CO2, CH4 (both types), and N2O, respectively.
  5. This 500-year GWP-weighted conversion factor for Methane (CH4), i.e., 7.6x, is based on figures in Table 2.14 from (IPCC, 2007), for which the 100-year GWP-weighted conversion factor was 25.0x and not 28.0x as per (IPCC, 2013). Given that the 100-year GWP conversion factor for Methane increased, therefore it seems reasonable to assume that the 500-year GWP conversion factor for Methane likewise has increased. Assuming that this increase is proportionate, the 500-year GWP conversion factor would be 8.5x (estimate), approximated by dividing 28x/25x=1.12 and multiplying the 7.6x by this figure, resulting in 7.6x1.12=8.5x. Thus, the 500-year GWP-weighted conversion factor for Methane may be closer to 8.5x and not 7.6x as per (IPCC, 2007). Keep in mind that this approximation, i.e., proportionate increase, is not scientifically informed and may not reflect the physical reality the world. Further, there are likely updated 500-year GWP conversion factors, that reflect best-available scientific knowledge, somewhere...
  6. The (IPCC, 2007) GWP conversion factors do not distinguish Fossil Methane, providing only a single GWP conversion factor for Methane.
  7. This 500-year GWP-weighted conversion factor for Nitrous oxide (N2O), i.e., 153x, is based on figures in Table 2.14 from (IPCC, 2007), for which the 100-year GWP-weighted conversion factor was 298x and not 265x as per (IPCC, 2013). Given that the 100-year GWP conversion factor for Methane decreased, therefore it seems reasonable to assume that the 500-year GWP conversion factor for Nitrous oxide likewise has decreased. Assuming that this decrease is proportionate, the 500-year GWP conversion factor would be 136x (estimate), approximated by dividing 265x/298x=0.89 and multiplying the 153x by this figure, resulting in 153x0.89=136x. Thus, the 500-year GWP-weighted conversion factor for Nitrous oxide may be closer to 136x and not 153x as per (IPCC, 2007). Keep in mind that this approximation, i.e., this proportionate increase, is not scientifically informed and my not reflect the physical reality of the real world. Further, there are likely updated 500-year GWP conversion factors, that reflect best-available scientific knowledge, somewhere...
  8. Archer, David, Michael Eby, Victor Brovkin, Andy Ridgwell, Long Cao, Uwe Mikolajewicz, Ken Caldeira, et al. "Atmospheric Lifetime of Fossil Fuel Carbon Dioxide." Annual Review of Earth and Planetary Sciences 37, no. 1 (April 27, 2009): 117-34. https://doi.org/10.1146/annurev.earth.031208.100206.
  9. 9.0 9.1 9.2 9.3 All figures are rounded to the nearest whole number despite the fact that in many instances the figures have and/or are decimals. The average is a simple average, i.e., it is not weighted based on the prevalence greenhouse gases within a specific category.
  10. 10.00 10.01 10.02 10.03 10.04 10.05 10.06 10.07 10.08 10.09 10.10 10.11 10.12 10.13 10.14 10.15 Several greenhouse gases have a GWP conversion factor of less than one (<1), however, for the purpose of approximating the simple average GWP conversion factor of these groups of greenhouse gases, any GWP conversion factors with a value of less than one is assumed to be equivalent to one, which increases the average, ever so slightly and/or insignificantly.
  11. 11.00 11.01 11.02 11.03 11.04 11.05 11.06 11.07 11.08 11.09 11.10 11.11 11.12 11.13 11.14 11.15 11.16 11.17 11.18 11.19 11.20 11.21 11.22 11.23 11.24 11.25 11.26 11.27 11.28 11.29 11.30 11.31 11.32 11.33 The only group of Other Trace Gases for which the 20- or 100-year ranges and average factors, and the 500-year ranges and average factors, are comparable, in full, is Chlorofluorocarbons (CFCs), for which the 20-, 100- and 500-year GWP datasets include GWP conversion factors for all CFCs (i.e., CFC-11, CFC-12, CFC-13, CFC-113, CFC-114, and CFC-115). For all remaining groups of Other Trace Gases, the 20-year and 100-year datasets include figures for more greenhouse gases than for the 500-year datasets. The 100-year and 20-year datasets include GWP conversion factors for, in total, two hundred and three (203) Other Trace Gases (i.e., not "Big Three"), both datasets originating from (IPCC, 2013). However, for the 500-year dataset, there are only ninety one (91) Other Trace Gases with GWP conversion factors originating from (IPCC, 2007). As such, the 20-/100-year and 500-year ranges (min-max) and simple averages are not comparable for all groups Other Trace Gases, apart from CFCs.
  12. Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakamjima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.[2]