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

=== Effective Radiative Forcing ===

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'''For carbon dioxide, methane, nitrous oxide and chlorofluorocarbons, there is now evidence to quantify the effect on ERF of tropospheric adjustments (e.g., from changes in atmospheric temperatures, clouds and water vapour). The assessed ERF for a doubling of carbon dioxide compared to 1750 levels (3.93 ± 0.47 W m''' –2 ''') is larger than in AR5.''' Effective radiative forcings (ERF), introduced in AR5, have been estimated for a larger number of agents and shown to be more closely related to the temperature response than the stratospheric-temperature adjusted radiative forcing. For carbon dioxide, the adjustments include the physiological effects on vegetation ( ''high confidence'' ). {7.3.2}

'''The total anthropogenic ERF over the industrial era''' ( '''1750–2019''' ''') was 2.72 [1.96 to 3.48] W m''' –2 '''. This estimate has increased by 0.43 W m''' –2 '''compared to AR5 estimates for 1750–2011.''' This increase includes +0.34 W m <sup>–2</sup> from increases in atmospheric concentrations of well-mixed greenhouse gases (including halogenated species) since 2011, +0.15 W m <sup>–2</sup> from upwards revisions of their radiative efficiencies and +0.10 W m <sup>–2</sup> from re-evaluation of the ozone and stratospheric water vapour ERF. The 0.59 W m <sup>–2</sup> increase in ERF from greenhouse gases is partly offset by a better-constrained assessment of total aerosol ERF that is more strongly negative than in AR5, based on multiple lines of evidence ( ''high confidence'' ). Changes in surface reflectance from land-use change, deposition of light-absorbing particles on ice and snow, and contrails and aviation-induced cirrus have also contributed to the total anthropogenic ERF over the industrial era, with –0.20 [–0.30 to –0.10] W m <sup>–2</sup> ( ''medium confidence'' ), +0.08 [0 to 0.18] W m <sup>–2</sup> ( ''low confidence'' ) and +0.06 [0.02 to 0.10] W m <sup>–2</sup> ( ''low confidence'' ), respectively. {7.3.2, 7.3.4, 7.3.5}

'''Anthropogenic emissions of greenhouse gases and their precursors contribute an ERF of 3.84 [3.46 to 4.22] W m''' –2 '''over the industrial era (1750–2019). Most of this total ERF, 3.32 [3.03 to 3.61] W m''' –2 ''', comes from the wel''' '''l-m''' '''ixed greenhouse gases, with changes in ozone and stratospheric water vapour (from methane oxidation) contributing the remainder.''' The ERF of greenhouse gases is composed of 2.16 [1.90 to 2.41] W m <sup>–2</sup> from carbon dioxide, 0.54 [0.43 to 0.65] W m <sup>–2</sup> from methane, 0.41 [0.33 to 0.49] W m <sup>–2</sup> from halogenated species, and 0.21 [0.18 to 0.24] W m <sup>–2</sup> from nitrous oxide. The ERF for ozone is 0.47 [0.24 to 0.71] W m <sup>–2</sup> . The estimate of ERF for ozone has increased since AR5 due to revised estimates of precursor emissions and better accounting for effects of tropospheric ozone precursors in the stratosphere. The estimated ERF for methane has slightly increased due to a combination of increases from improved spectroscopic treatments being somewhat offset by accounting for adjustments ( ''high confidence'' ). {7.3.2, 7.3.5}

'''Aerosols contribute an ERF of –1.3 [–2.0 to –0.6] W m''' –2 '''over the industrial era (1750–2014)''' ( ''medium confidence'' '''). The ERF due to aerosol–cloud interactions (ERFaci) contributes most to the magnitude of the total aerosol ERF''' ( ''high confidence'' ''') and is assessed to be –1.0 [–1.7 to –0.3] W m''' –2 ( ''medium confidence'' '''), with the remainder due to aerosol–radiation interactions (ERFari), assessed to be –0.3 [–0.6 to 0.0] W m''' –2 ( ''medium confidence'' ''').''' There has been an increase in the estimated magnitude but a reduction in the uncertainty of the total aerosol ERF relative to AR5, supported by a combination of increased process-understanding and progress in modelling and observational analyses. ERF estimates from these separate lines of evidence are now consistent with each other, in contrast to AR5, and support the assessment that it is ''virtually certain'' that the total aerosol ERF is negative. Compared to AR5, the assessed magnitude of ERFaci has increased, while the magnitude of ERFari has decreased ''.'' The total aerosol ERF over the period 1750–2019 is less certain than the headline statement assessment. It is also assessed to be smaller in magnitude at –1.1 [–1.7 to –0.4] W m <sup>–2</sup> , primarily due to recent emissions changes ( ''medium confidence'' ). {7.3.3, 7.3.5, 2.2.6}

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