TY - JOUR

T1 - Assessment of pre-industrial to present-day anthropogenic climate forcing in UKESM1

AU - O'Connor, Fiona M.

AU - Luke Abraham, N.

AU - Dalvi, Mohit

AU - Folberth, Gerd A.

AU - Griffiths, Paul T.

AU - Hardacre, Catherine

AU - Johnson, Ben T.

AU - Kahana, Ron

AU - Keeble, James

AU - Kim, Byeonghyeon

AU - Morgenstern, Olaf

AU - Mulcahy, Jane P.

AU - Richardson, Mark

AU - Robertson, Eddy

AU - Seo, Jeongbyn

AU - Shim, Sungbo

AU - Teixeira, João C.

AU - Turnock, Steven T.

AU - Williams, Jonny

AU - Wiltshire, Andrew J.

AU - Woodward, Stephanie

AU - Zeng, Guang

N1 - Publisher Copyright: © 2021 Author(s).

PY - 2021/1/29

Y1 - 2021/1/29

N2 - Quantifying forcings from anthropogenic perturbations to the Earth system (ES) is important for understanding changes in climate since the pre-industrial (PI) period. Here, we quantify and analyse a wide range of present-day (PD) anthropogenic effective radiative forcings (ERFs) with the UK's Earth System Model (ESM), UKESM1, following the protocols defined by the Radiative Forcing Model Intercomparison Project (RFMIP) and the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP). In particular, quantifying ERFs that include rapid adjustments within a full ESM enables the role of various chemistry-aerosol-cloud interactions to be investigated. Global mean ERFs for the PD (year 2014) relative to the PI (year 1850) period for carbon dioxide (CO2), nitrous oxide (N2O), ozone-depleting substances (ODSs), and methane (CH4) are 1.89 ± 0.04, 0.25 ± 0.04,-0.18 ± 0.04, and 0.97 ± 0.04 W m-2, respectively. The total greenhouse gas (GHG) ERF is 2.92 ± 0.04 W m-2. UKESM1 has an aerosol ERF of-1.09 ± 0.04 W m-2. A relatively strong negative forcing from aerosol-cloud interactions (ACI) and a small negative instantaneous forcing from aerosol-radiation interactions (ARI) from sulfate and organic carbon (OC) are partially offset by a substantial forcing from black carbon (BC) absorption. Internal mixing and chemical interactions imply that neither the forcing from ARI nor ACI is linear, making the aerosol ERF less than the sum of the individual speciated aerosol ERFs. Ozone (O3) precursor gases consisting of volatile organic compounds (VOCs), carbon monoxide (CO), and nitrogen oxides (NOx), but excluding CH4, exert a positive radiative forcing due to increases in O3. However, they also lead to oxidant changes, which in turn cause an indirect aerosol ERF. The net effect is that the ERF from PD-PI changes in NOx emissions is negligible at 0.03 ± 0.04 W m-2, while the ERF from changes in VOC and CO emissions is 0.33 ± 0.04 W m-2. Together, aerosol and O3 precursors (called near-term climate forcers (NTCFs) in the context of AerChemMIP) exert an ERF of-1.03 ± 0.04 W m-2, mainly due to changes in the cloud radiative effect (CRE). There is also a negative ERF from land use change (-0.17 ± 0.04 W m-2). When adjusted from year 1850 to 1700, it is more negative than the range of previous estimates, and is most likely due to too strong an albedo response. In combination, the net anthropogenic ERF (1.76 ± 0.04 W m-2) is consistent with other estimates. By including interactions between GHGs, stratospheric and tropospheric O3, aerosols, and clouds, this work demonstrates the importance of ES interactions when quantifying ERFs. It also suggests that rapid adjustments need to include chemical as well as physical adjustments to fully account for complex ES interactions.

AB - Quantifying forcings from anthropogenic perturbations to the Earth system (ES) is important for understanding changes in climate since the pre-industrial (PI) period. Here, we quantify and analyse a wide range of present-day (PD) anthropogenic effective radiative forcings (ERFs) with the UK's Earth System Model (ESM), UKESM1, following the protocols defined by the Radiative Forcing Model Intercomparison Project (RFMIP) and the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP). In particular, quantifying ERFs that include rapid adjustments within a full ESM enables the role of various chemistry-aerosol-cloud interactions to be investigated. Global mean ERFs for the PD (year 2014) relative to the PI (year 1850) period for carbon dioxide (CO2), nitrous oxide (N2O), ozone-depleting substances (ODSs), and methane (CH4) are 1.89 ± 0.04, 0.25 ± 0.04,-0.18 ± 0.04, and 0.97 ± 0.04 W m-2, respectively. The total greenhouse gas (GHG) ERF is 2.92 ± 0.04 W m-2. UKESM1 has an aerosol ERF of-1.09 ± 0.04 W m-2. A relatively strong negative forcing from aerosol-cloud interactions (ACI) and a small negative instantaneous forcing from aerosol-radiation interactions (ARI) from sulfate and organic carbon (OC) are partially offset by a substantial forcing from black carbon (BC) absorption. Internal mixing and chemical interactions imply that neither the forcing from ARI nor ACI is linear, making the aerosol ERF less than the sum of the individual speciated aerosol ERFs. Ozone (O3) precursor gases consisting of volatile organic compounds (VOCs), carbon monoxide (CO), and nitrogen oxides (NOx), but excluding CH4, exert a positive radiative forcing due to increases in O3. However, they also lead to oxidant changes, which in turn cause an indirect aerosol ERF. The net effect is that the ERF from PD-PI changes in NOx emissions is negligible at 0.03 ± 0.04 W m-2, while the ERF from changes in VOC and CO emissions is 0.33 ± 0.04 W m-2. Together, aerosol and O3 precursors (called near-term climate forcers (NTCFs) in the context of AerChemMIP) exert an ERF of-1.03 ± 0.04 W m-2, mainly due to changes in the cloud radiative effect (CRE). There is also a negative ERF from land use change (-0.17 ± 0.04 W m-2). When adjusted from year 1850 to 1700, it is more negative than the range of previous estimates, and is most likely due to too strong an albedo response. In combination, the net anthropogenic ERF (1.76 ± 0.04 W m-2) is consistent with other estimates. By including interactions between GHGs, stratospheric and tropospheric O3, aerosols, and clouds, this work demonstrates the importance of ES interactions when quantifying ERFs. It also suggests that rapid adjustments need to include chemical as well as physical adjustments to fully account for complex ES interactions.

U2 - 10.5194/acp-21-1211-2021

DO - 10.5194/acp-21-1211-2021

M3 - Journal article

AN - SCOPUS:85100508615

VL - 21

SP - 1211

EP - 1243

JO - Atmospheric Chemistry and Physics

JF - Atmospheric Chemistry and Physics

SN - 1680-7316

IS - 2

ER -