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

==== 7.3.5.1 Major Changes in Forcing since the IPCC Fifth Assessment Report ====

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The AR5 introduced the concept of effective radiative forcing (ERF) and radiative adjustments, and made a preliminary assessment that the tropospheric adjustments were zero for all species other than the effects of aerosol–cloud interaction and black carbon. Since AR5, new studies have allowed for a tentative assessment of values for tropospheric adjustments to CO <sub>2</sub> , CH <sub>4</sub> , N <sub>2</sub> O, some CFCs, solar forcing, and stratospheric aerosols, and to place a tighter constraint on adjustments from aerosol–cloud interaction (Sections 7.3.2, 7.3.3 and 7.3.4). In AR6, the definition of ERF explicitly removes the land-surface temperature change as part of the forcing, in contrast to AR5 where only sea surface temperatures were fixed. The ERF is assessed to be a better predictor of modelled equilibrium temperature change (i.e., less variation in feedback parameter) than SARf ( [[#7.3.1|Section 7.3.1]] ).

As discussed in ( [[#7.3.2|Section 7.3.2]] , the radiative efficiencies for CO <sub>2</sub> , CH <sub>4</sub> and N <sub>2</sub> O have been updated since AR5 ( [[#Etminan--2016|Etminan et al., 2016]] ). There has been a small (1%) increase in the stratospheric-temperature-adjusted CO <sub>2</sub> radiative efficiency, and a +5% tropospheric adjustment has been added. The stratospheric-temperature-adjusted radiative efficiency for CH <sub>4</sub> is increased by approximately 25% ( ''high confidence'' ). The tropospheric adjustment is tentatively assessed to be –14% ( ''low confidence'' ). A +7% tropospheric adjustment has been added to the radiative efficiency for N <sub>2</sub> O and +12% to CFC-11 and CFC-12 ( ''low confidence'' ).

For aerosols there has been a convergence of model and observational estimates of aerosol forcing, and the partitioning of the total aerosol ERF has changed. Compared to AR5 a greater fraction of the ERF is assessed to come from ERFaci compared to the ERFari. It is now assessed as ''virtually certain'' that the total aerosol ERF (ERFari+aci) is negative.

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