Editing IPCC:AR6/WGI/Chapter-2 (section)

==== 2.2.3.3 Modern Measurements of WMGHGs ====

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In this section and for calculation of ERF, surface global averages are determined from measurements representative of the well-mixed lower troposphere. Global averages that include sites subject to significant anthropogenic activities or influenced by strong regional biospheric emissions are typically larger than those from remote sites, and require weighting accordingly (Table 2.2). This section focusses on global mean mixing ratios estimated from networks with global spatial coverage, and updated from the CMIP6 historical dataset ( [[#Meinshausen--2017|Meinshausen et al., 2017]] ) for periods prior to the existence of global networks.

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Table 2.2 '''|''' '''Atmospheric global annual mean mixing ratios (dry-air mole fraction) for well-mixed greenhouse gases.''' The table provides observed values for 2011 and 2019, and relative changes since 2011, for selected well-mixed, radiatively important gases (ERF &gt;0.001 W m <sup>–2</sup> ), estimated from various measurement networks or compilations. Units are parts per million (ppm) for CO <sub>2</sub> , parts per billion (ppb) for CH <sub>4</sub> and N <sub>2</sub> O, parts per trillion (ppt) for all other gases. Time series since 1750, data for additional gases, references, and network information can be found in [[IPCC:Wg1:Chapter:Annex-iii|Annex III]] and the corresponding electronic supplement. Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).

{| class="wikitable"
|-
| '''Species'''

| '''Lifetime,'''

'''AR6, ERF'''

| '''2011'''

| '''2019'''

| '''Change'''

| '''Network'''

| rowspan="35"|
| '''Species'''

| '''Lifetime,'''

'''AR6, ERF'''

| '''2011'''

| '''2019'''

| '''Change'''

| '''Network'''

|-
| rowspan="5"| '''CO''' <sub>2</sub>

| \#

| 390.5

| 409.9 (0.17)

| 5.0%

| NOAA* <sup>a</sup>

| rowspan="3"| '''HCFC-22'''

| 11.9

| 212.6

| 246.8 (0.5)

| 16.1%

| NOAA*

|-
| 409.9 (0.4)

| 389.7

| 409.5 (0.37)

| 5.1%

| SIO

| 246.8 (0.6)

| 213.7

| 246.7 (0.4)

| 15.5%

| AGAGE*

|-
| 2.156

| 390.2

| 409.6 (0.31)

| 5.0%

| CSIRO

| 0.053

| 209.0

| 244.1 (3.0)

| 22.0%

| UCI

|-
|
| 390.9

| 410.5 (0.30)

| 5.0%

| WMO

| rowspan="3"| '''HCFC-141b'''

| 9.4

| 21.3

| 24.4 (0.1)

| 14.4%

| NOAA*

|-
|
| 390.9

|
| CMIP6

| 24.4 (0.3)

| 21.4

| 24.3 (0.1)

| 13.7%

| AGAGE*

|-
| rowspan="6"| '''CH''' <sub>4</sub>

| 9.1–11.8

| 1803.1

| 1866.6 (1.0)

| 3.5%

| NOAA*

| 0.004

| 20.8

| 26.0 (0.3)

| 25.0%

| UCI

|-
| 1866.3 (3.3)

| 1803.6

| 1866.1 (2.0)

| 3.5%

| AGAGE*

| rowspan="3"| '''HCFC-142b'''

| 18

| 20.9

| 22.0 (0.1)

| 5.3%

| NOAA*

|-
| 0.544

| 1791.8

| 1860.8 (3.5)

| 3.9%

| UCI

| 22.3 (0.4)

| 21.5

| 22.5 (0.1)

| 5.0%

| AGAGE*

|-
|
| 1802.3

| 1862.5 (2.4)

| 3.3%

| CSIRO

| 0.004

| 21.0

| 22.8 (0.2)

| 8.6%

| UCI

|-
|
| 1813

| 1877 (3)

| 3.5%

| WMO

| rowspan="3"| '''HFC-134a'''

| 14

| 62.7

| 107.8 (0.4)

| 72%

| NOAA*

|-
|
| 1813.1

|
| CMIP6

| 107.6 (1.0)

| 62.8

| 107.4 (0.2)

| 71%

| AGAGE*

|-
| rowspan="5"| '''N''' <sub>2</sub> '''O'''

| 116–109

| 324.2

| 331.9 (0.2)

| 2.4%

| NOAA*

| 0.018

| 63.4

| 107.6 (1.7)

| 70%

| UCI

|-
| 332.1 (0.4)

| 324.7

| 332.3 (0.1)

| 2.4%

| AGAGE*

| rowspan="3"| '''HFC-125'''

| 30

| 10.1

| 29.1 (0.3)

| 187%

| NOAA*

|-
| 0.208

| 324.0

| 331.6 (0.3)

| 2.3%

| CSIRO

| 29.4 (0.6)

| 10.4

| 29.7 (0.1)

| 186%

| AGAGE*

|-
|
| 324.3

| 332.0 (0.2)

| 2.4%

| WMO

| 0.007

|
|-
|
| 324.2

|
| CMIP6

| rowspan="3"| '''HFC-23'''

| 228

| 24.1

| 32.4 (0.1)

| 35%

| AGAGE*

|-
| rowspan="3"| '''CFC-12'''

| 102

| 526.9

| 501.5 (0.3)

| –4.8%

| NOAA*

| 32.4 (0.1)

|
|-
| 503.1 (3.2)

| 529.6

| 504.6 (0.2)

| –4.7%

| AGAGE*

| 0.006

|
|-
| 0.180

| 525.3

| 508.4 (2.5)

| –3.2%

| UCI

| rowspan="3"| '''HFC-143a'''

| 51

| 11.9

| 23.8 (0.1)

| 100%

| NOAA*

|-
| rowspan="3"| '''CFC-11'''

| 52

| 237.2

| 226.5 (0.2)

| –4.5%

| NOAA*

| 24.0 (0.4)

| 12.1

| 24.2 (0.1)

| 100%

| AGAGE*

|-
| 226.2 (1.1)

| 237.4

| 225.9 (0.1)

| –4.8%

| AGAGE*

| 0.004

|
|-
| 0.066

| 237.9

| 224.9 (1.3)

| –5.5%

| UCI

| rowspan="3"| '''HFC-32'''

| 5.4

| 4.27

| 19.2 (0.3)

| 350%

| NOAA*

|-
| rowspan="3"| '''CFC-113'''

| 93

| 74.5

| 69.7 (0.1)

| –6.4%

| NOAA*

| 20.0 (1.4)

| 5.15

| 20.8 (0.2)

| 304%

| AGAGE*

|-
| 69.8 (0.3)

| 74.6

| 69.9 (0.1)

| –6.3%

| AGAGE*

| 0.002

|
|-
| 0.021

| 74.9

| 70.0 (0.5)

| –6.5%

| UCI

| rowspan="3"| '''CF''' <sub>4</sub>

| 50,000

| 79.0

| 85.5 (0.1)

| 8.2%

| AGAGE*

|-
| rowspan="3"| '''CFC-114'''

| 189

| 16.36

| 16.28 (0.03)

| –0.5%

| AGAGE*

| 85.5 (0.2)

|
|-
| 16.0 (0.05)

|
| 0.005

|
|-
| 0.005

|
| rowspan="3"| '''C''' <sub>2</sub> '''F''' <sub>6</sub>

| 10,000

| 4.17

| 4.85 (0.01)

| 16.3%

| AGAGE*

|-
| rowspan="3"| '''CFC-115'''

| 540

| 8.39

| 8.67 (0.02)

| 3.3%

| AGAGE*

| 4.85 (0.1)

|
|-
| 8.67 (0.02)

|
| 0.001

|
|-
| 0.002

|
| rowspan="3"| '''SF''' <sub>6</sub> <sub></sub>

| About 1000

| 7.32

| 9.96 (0.02)

| 36.1%

| NOAA*

|-
| rowspan="3"| '''CCl''' <sub>4</sub>

| 32

| 86.9

| 78.4 (0.1)

| –9.8%

| NOAA*

| 9.95 (0.01)

| 7.28

| 9.94 (0.02)

| 36.5%

| AGAGE*

|-
| 77.9 (0.7)

| 85.3

| 77.3 (0.1)

| –9.4%

| AGAGE*

| 0.006

|
|-
| 0.013

| 87.8

| 77.7 (0.7)

| –11.5%

| UCI

|
|}

AGAGE: Advanced Global Atmospheric Gases Experiment; SIO: Scripps Institution of Oceanography; NOAA: National Oceanic and Atmospheric Administration, Global Monitoring Laboratory; UCI: University of California, Irvine; CSIRO: Commonwealth Scientific and Industrial Research Organization, Aspendale, Australia; WMO: World Meteorological Organization, Global Atmosphere Watch, CMIP6 (Climate Model Intercomparison Project Phase 6). Mixing ratios denoted by AR6 are representative of the remote, unpolluted troposphere, derived from one or more measurement networks (denoted by *). Minor differences between 2011 values reported here and in the previous Assessment Report (AR5) are due to updates in calibration and data processing. ERF in 2019 is taken from Table 7.5, and the difference with the AR5 assessment reflects updates in the estimates of AR6 global mixing ratios and updated radiative calculations. Uncertainties, in parenthesis, are estimated at 90% confidence interval. Networks use different methods to estimate uncertainties. Some uncertainties have been rounded up to be consistent with the number of decimal places shown. Lifetime is reported in years: # indicates multiple lifetimes for CO <sub>2</sub> . For CH <sub>4</sub> and N <sub>2</sub> O the two values represent total atmospheric lifetime and perturbation lifetime.

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<span id="carbon-dioxide-co-2-1"></span>
===== 2.2.3.3.1 Carbon dioxide (CO <sub>2</sub> ) =====

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There has been a positive trend in globally averaged surface CO <sub>2</sub> mixing ratios since 1958 (Figure 2.5a), that reflects the imbalance of sources and sinks (Section 5.2). The growth rate has increased overall since the 1960s (Figure 2.5a inset), while annual growth rates have varied substantially, for example, reaching a peak during the strong El Niño events of 1997–1998 and 2015–2016 ( [[#Bastos--2013|Bastos et al., 2013]] ; [[#Betts--2016|Betts et al., 2016]] ). The average annual CO <sub>2</sub> increase from 2000 through 2011 was 2.0 ppm yr <sup>–1</sup> (standard deviation 0.3 ppm yr <sup>–1</sup> ), similar to what was reported in AR5. From 2011 through 2019 it was 2.4 ppm yr <sup>–</sup> <sup>1</sup> (standard deviation 0.5 ppm yr <sup>–1</sup> ), which is higher than that of any comparable time period since global measurements began. Global networks consistently show that the globally averaged annual mean CO <sub>2</sub> has increased by 5.0% since 2011, reaching 409.9 ± 0.4 ppm in 2019 (NOAA measurements). Further assessment of changing seasonality is undertaken in [[#2.3.4.1|Section 2.3.4.1]] .

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[[File:3e2fe664c93efaa7c3c0198d50490cdd IPCC_AR6_WGI_Figure_2_5.png]]

'''Figure 2.5 |''' '''Globally averaged dry-air mole fractions of greenhouse gases. (a)''' CO <sub>2</sub> from SIO, CSIRO, and NOAA/GML '''(b)''' CH <sub>4</sub> from NOAA, AGAGE, CSIRO, and UCI; and '''(c)''' N <sub>2</sub> O from NOAA, AGAGE, and CSIRO (Table 2.2). Growth rates, calculated as the time derivative of the global means after removing seasonal cycle are shown as inset figures. Note that the CO <sub>2</sub> series is 1958–2019 whereas CH <sub>4</sub> , and N <sub>2</sub> O are 1979–2019. Units are parts per million (ppm) or parts per billion (ppb). Further details on data are in Annex III, and on data sources and processing are available in the chapter data table (Table 2.SM.1).

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<span id="methane-ch-4-1"></span>
===== 2.2.3.3.2 Methane (CH <sub>4</sub> ) =====

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The globally averaged surface mixing ratio of CH <sub>4</sub> in 2019 was 1866.3 ± 3.3 ppb, which is 3.5% higher than 2011, while observed increases from various networks range from 3.3–3.9% (Table 2.2 and Figure 2.5b). There are marked growth rate changes over the period of direct observations, with a decreasing rate from the late-1970s through the late-1990s, very little change in concentrations from 1999–2006, and resumed increases since 2006. Atmospheric CH <sub>4</sub> fluctuations result from complex variations of sources and sinks. A detailed discussion of recent methane trends and our understanding of their causes is presented in Cross-Chapter Box 5.2.

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<span id="nitrous-oxide-n-2-o-1"></span>
===== 2.2.3.3.3 Nitrous oxide (N <sub>2</sub> O) =====

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The AR5 reported 324.2 ± 0.1 ppb for global surface annual mean N <sub>2</sub> O in 2011; since then, it has increased by 2.4% to 332.1 ± 0.4 ppb in 2019. Independent measurement networks agree well for both the global mean mixing ratio and relative change since 2011 (Table 2.2). Over 1995–2011, N <sub>2</sub> O increased at an average rate of 0.79 ± 0.05 ppb yr <sup>–1</sup> . The growth rate has been higher in recent years, amounting to 0.96 ± 0.05 ppb yr <sup>–</sup> <sup>1</sup> from 2012 to 2019 (Figure 2.5c and Section 5.2.3.5).

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