Effective radiative forcing from emissions of reactive gases and aerosols – a multi-model comparison

Abstract

Abstract. This paper quantifies the pre-industrial (1850) to present-day (2014) effective radiative forcing (ERF) of anthropogenic emissions of NOX, volatile organic compounds (VOCs; including CO), SO2, NH3, black carbon, organic carbon, and concentrations of methane, N2O and ozone-depleting halocarbons, using CMIP6 models. Concentration and emission changes of reactive species can cause multiple changes in the composition of radiatively active species: tropospheric ozone, stratospheric ozone, stratospheric water vapour, secondary inorganic and organic aerosol, and methane. Where possible we break down the ERFs from each emitted species into the contributions from the composition changes. The ERFs are calculated for each of the models that participated in the AerChemMIP experiments as part of the CMIP6 project, where the relevant model output was available. The 1850 to 2014 multi-model mean ERFs (± standard deviations) are −1.03 ± 0.37 W m−2 for SO2 emissions, −0.25 ± 0.09 W m−2 for organic carbon (OC), 0.15 ± 0.17 W m−2 for black carbon (BC) and −0.07 ± 0.01 W m−2 for NH3. For the combined aerosols (in the piClim-aer experiment) it is −1.01 ± 0.25 W m−2. The multi-model means for the reactive well-mixed greenhouse gases (including any effects on ozone and aerosol chemistry) are 0.67 ± 0.17 W m−2 for methane (CH4), 0.26 ± 0.07 W m−2 for nitrous oxide (N2O) and 0.12 ± 0.2 W m−2 for ozone-depleting halocarbons (HC). Emissions of the ozone precursors nitrogen oxides (NOx), volatile organic compounds and both together (O3) lead to ERFs of 0.14 ± 0.13, 0.09 ± 0.14 and 0.20 ± 0.07 W m−2 respectively. The differences in ERFs calculated for the different models reflect differences in the complexity of their aerosol and chemistry schemes, especially in the case of methane where tropospheric chemistry captures increased forcing from ozone production.

Energy Budget Constraints on the Time History of Aerosol Forcing and Climate Sensitivity

“…Including carbonaceous aerosol in Equation represented by the sum of BC and OC emissions is useful as some CMIP6 models include the effects of BC and/or OC on the change in cloud condensation nuclei. The resulting aerosol‐cloud interactions can be substantial, for example, a negative ERFaci to BC emissions in the MIROC6 model (Thornhill et al., 2021). Equation is found to give a good heuristic approximation of global‐mean ERFaci to a more sophisticated aerosol indirect effect model (Ghan et al., 2013) as shown in Smith, Forster, et al.…”

“…In reality, nitrate formation may compete with sulphate formation for available ammonium. Model evidence suggests this is of limited importance historically (Thornhill et al, 2021), but may become more important in future scenarios where the nitrate to sulphate emissions ratio is projected to increase (Bellouin et al, 2011;Hauglustaine et al, 2014 x for small x). The degree of logarithmic behavior that ERFaci exhibits to emissions differ considerably between GCMs (Wilcox et al, 2015), and the possibility that ERFaci may be linear with emissions in some CMIP5 models was discussed in Booth et al (2018).…”

FaIRv2.0.0: a generalized impulse response model for climate uncertainty and future scenario exploration

“…Recent studies (Richardson et al, 2016(Richardson et al, , 2018 have shown that the definition of globally averaged surface temperature used is important when comparing observations to climate model output, and is relevant when exploring policy-relevant quantities such as the carbon budget (Tokarska et al, 2019). Discrepancies arise since observations blend air temperatures over land and sea ice with water temperature over ocean and do not have full global coverage (they are blendedmasked), while climate model surface temperature output is globally complete and always measured as the air temperature 2 m above the surface of the Earth.…”

Potential Source Regions and Transportation Pathways of Reactive Gases at a Regional Background Site in Northwestern China

“…In addition to the effects of natural and manmade sources on atmospheric concentrations of SO 2 , NO 2 , O 3 , and CO, regional-and global-scale atmospheric transport also affect atmospheric concentrations of these species, which can lead to changes in the climate system. For these reasons, these are currently popular research topics in the fields of Earth and environmental science [8][9][10].…”