Editing IPCC:AR6/WGI/Chapter-7 (section)

===== 7.3.3.1.3 Overall assessment of IRFari and ERFari =====

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The observation-based assessment of IRFari of –0.4 ± 0.4 W m <sup>–2</sup> and the corresponding model-based assessment of –0.2 ± 0.2 W m <sup>–2</sup> can be compared to the range of –0.45 to –0.05 W m <sup>–2</sup> that emerged from a comprehensive review in which an observation-based estimate of anthropogenic AOD was combined with model-derived ranges for all relevant aerosol radiative properties ( [[#Bellouin--2020|Bellouin et al., 2020]] ). Based on the above, IRFari is assessed to be –0.25 ± 0.2 W m <sup>–2</sup> ( ''medium confidence'' ).

ERFari from model-based evidence is –0.25 ± 0.25 W m <sup>–2</sup> , which suggests a small negative adjustment relative to the model-based IRFari estimate, consistent with the literature discussed in ( [[#7.3.3.1.2|Section 7.3.3.1.2]] . Adding this small adjustment to our assessed IRFari estimate of –0.25 W m <sup>–2</sup> , and accounting for additional uncertainty in the adjustments, ERFari is assessed to –0.3 ± 0.3 ( ''medium confidence'' ). This assessment is consistent with the 5–95% confidence range for ERFari in [[#Bellouin--2020|Bellouin et al. (2020)]] of –0.71 to –0.14 W m <sup>–2</sup> , and notably implies that it is ''very likely'' that ERFari is negative. Differences relative to [[#Bellouin--2020|Bellouin et al. (2020)]] reflect the range of estimates in Table 7.6 and the fact that an ERFari more negative than –0.6 W m <sup>–2</sup> would require adjustments that considerably augment the assessed IRFari, which is not supported by the assessed literature.

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'''Table 7.6''' '''|''' '''Present-day effective radiative forcing (ERF) due to changes in aerosol–radiation interactions (ERFari) and changes in aerosol–cloud interactions (ERFaci), and total aerosol ERF (ERFari+aci)''' from GCM CMIP6 (2014 relative to 1850; [[#Smith--2020b|Smith et al., 2020b]] and later model results) and CMIP5 (year 2000 relative to 1860; [[#Zelinka--2014|Zelinka et al., 2014]] ). CMIP6 results are simulated as part of RFMIP ( [[#Pincus--2016|Pincus et al., 2016]] ). An additional 5% is applied to the CMIP5 and CMIP6 model results to account for land-surface cooling (Figure 7.4; [[#Smith--2020a|Smith et al., 2020a]] ).

{| class="wikitable"
|-
| Models

| ERFari

(W m <sup>–2</sup> )

| ERFaci

(W m <sup>–2</sup> )

| ERFari+aci

(W m <sup>–2</sup> )

|-
| ACCESS-CM2

| –0.24

| –0.93

| –1.17

|-
| ACCESS-ESM1-5

| –0.07

| –1.19

| –1.25

|-
| BCC-ESM1

| –0.79

| –0.69

| –1.48

|-
| CanESM5

| –0.02

| –1.09

| –1.11

|-
| CESM2

| +0.15

| –1.65

| –1.50

|-
| CNRM-CM6-1

| –0.28

| –0.86

| –1.14

|-
| CNRM-ESM2-1

| –0.15

| –0.64

| –0.79

|-
| EC-Earth3

| –0.39

| –0.50

| –0.89

|-
| GFDL-CM4

| –0.12

| –0.72

| –0.84

|-
| GFDL-ESM4

| –0.06

| –0.84

| –0.90

|-
| GISS-E2-1-G (physics_version=1)

| –0.55

| –0.81

| –1.36

|-
| GISS-E2-1-G (physics_version=3)

| –0.64

| –0.39

| –1.02

|-
| HadGEM3-GC31-LL

| –0.29

| –0.87

| –1.17

|-
| IPSL-CM6A-LR

| –0.39

| –0.29

| –0.68

|-
| IPSL-CM6A-LR-INCA

| –0.45

| –0.35

| –0.80

|-
| MIROC6

| –0.22

| –0.77

| –0.99

|-
| MPI-ESM-1-2-HAM

| +0.10

| –1.40

| –1.31

|-
| MRI-ESM2-0

| –0.48

| –0.74

| –1.22

|-
| NorESM2-LM

| –0.15

| –1.08

| –1.23

|-
| NorESM2-MM

| –0.03

| –1.26

| –1.29

|-
| UKESM1-0-LL

| –0.20

| –0.99

| –1.19

|-
| CMIP6 average and 5–95% confidence range (2014 relative to 1850)

| –0.25 ± 0.40

| –0.86 ± 0.57

| –1.11 ± 0.38

|-
| CMIP5 average and 5–95% confidence range (2000 relative to 1860)

| –0.27 ± 0.35

| –0.96 ± 0.55

| –1.23 ± 0.48

|}

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