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Title: Effective radiative forcing and adjustments in CMIP6 models

Abstract

Abstract. The effective radiative forcing, which includes the instantaneous forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective radiative forcing and adjustments in 17 contemporary climate models that are participating in the Coupled Model Intercomparison Project (CMIP6) and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global-mean anthropogenic forcing relative to pre-industrial (1850) levels from climate models stands at 2.00 (±0.23) W m−2, comprised of 1.81 (±0.09) W m−2 from CO2, 1.08 (± 0.21) W m−2 from other well-mixed greenhouse gases, −1.01 (± 0.23) W m−2 from aerosols and −0.09 (±0.13) W m−2 from land use change. Quoted uncertainties are 1 standard deviation across model best estimates, and 90 % confidence in the reported forcings, due to internal variability, is typically within 0.1 W m−2. The majority of the remaining 0.21 W m−2 is likely to be from ozone. In most cases, the largest contributors to the spread in effective radiative forcing (ERF) is from the instantaneous radiative forcing (IRF) and from cloud responses, particularly aerosol–cloud interactions to aerosol forcing. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the stratospherically adjusted radiative forcing ismore » approximately equal to ERF for greenhouse gas forcing but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol forcing ranges from −0.63 to −1.37 W m−2, exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO2 forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol forcing is uncorrelated with climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol forcing and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol forcing to recreate observed historical warming.« less

Authors:
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Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER)
OSTI Identifier:
1647673
Alternate Identifier(s):
OSTI ID: 1770589
Grant/Contract Number:  
7457436; 1582977
Resource Type:
Journal Article: Published Article
Journal Name:
Atmospheric Chemistry and Physics (Online)
Additional Journal Information:
Journal Name: Atmospheric Chemistry and Physics (Online) Journal Volume: 20 Journal Issue: 16; Journal ID: ISSN 1680-7324
Publisher:
Copernicus Publications, EGU
Country of Publication:
Germany
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Smith, Christopher J., Kramer, Ryan J., Myhre, Gunnar, Alterskjær, Kari, Collins, William, Sima, Adriana, Boucher, Olivier, Dufresne, Jean-Louis, Nabat, Pierre, Michou, Martine, Yukimoto, Seiji, Cole, Jason, Paynter, David, Shiogama, Hideo, O'Connor, Fiona M., Robertson, Eddy, Wiltshire, Andy, Andrews, Timothy, Hannay, Cécile, Miller, Ron, Nazarenko, Larissa, Kirkevåg, Alf, Olivié, Dirk, Fiedler, Stephanie, Lewinschal, Anna, Mackallah, Chloe, Dix, Martin, Pincus, Robert, and Forster, Piers M. Effective radiative forcing and adjustments in CMIP6 models. Germany: N. p., 2020. Web. doi:10.5194/acp-20-9591-2020.
Smith, Christopher J., Kramer, Ryan J., Myhre, Gunnar, Alterskjær, Kari, Collins, William, Sima, Adriana, Boucher, Olivier, Dufresne, Jean-Louis, Nabat, Pierre, Michou, Martine, Yukimoto, Seiji, Cole, Jason, Paynter, David, Shiogama, Hideo, O'Connor, Fiona M., Robertson, Eddy, Wiltshire, Andy, Andrews, Timothy, Hannay, Cécile, Miller, Ron, Nazarenko, Larissa, Kirkevåg, Alf, Olivié, Dirk, Fiedler, Stephanie, Lewinschal, Anna, Mackallah, Chloe, Dix, Martin, Pincus, Robert, & Forster, Piers M. Effective radiative forcing and adjustments in CMIP6 models. Germany. https://doi.org/10.5194/acp-20-9591-2020
Smith, Christopher J., Kramer, Ryan J., Myhre, Gunnar, Alterskjær, Kari, Collins, William, Sima, Adriana, Boucher, Olivier, Dufresne, Jean-Louis, Nabat, Pierre, Michou, Martine, Yukimoto, Seiji, Cole, Jason, Paynter, David, Shiogama, Hideo, O'Connor, Fiona M., Robertson, Eddy, Wiltshire, Andy, Andrews, Timothy, Hannay, Cécile, Miller, Ron, Nazarenko, Larissa, Kirkevåg, Alf, Olivié, Dirk, Fiedler, Stephanie, Lewinschal, Anna, Mackallah, Chloe, Dix, Martin, Pincus, Robert, and Forster, Piers M. 2020. "Effective radiative forcing and adjustments in CMIP6 models". Germany. https://doi.org/10.5194/acp-20-9591-2020.
@article{osti_1647673,
title = {Effective radiative forcing and adjustments in CMIP6 models},
author = {Smith, Christopher J. and Kramer, Ryan J. and Myhre, Gunnar and Alterskjær, Kari and Collins, William and Sima, Adriana and Boucher, Olivier and Dufresne, Jean-Louis and Nabat, Pierre and Michou, Martine and Yukimoto, Seiji and Cole, Jason and Paynter, David and Shiogama, Hideo and O'Connor, Fiona M. and Robertson, Eddy and Wiltshire, Andy and Andrews, Timothy and Hannay, Cécile and Miller, Ron and Nazarenko, Larissa and Kirkevåg, Alf and Olivié, Dirk and Fiedler, Stephanie and Lewinschal, Anna and Mackallah, Chloe and Dix, Martin and Pincus, Robert and Forster, Piers M.},
abstractNote = {Abstract. The effective radiative forcing, which includes the instantaneous forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective radiative forcing and adjustments in 17 contemporary climate models that are participating in the Coupled Model Intercomparison Project (CMIP6) and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global-mean anthropogenic forcing relative to pre-industrial (1850) levels from climate models stands at 2.00 (±0.23) W m−2, comprised of 1.81 (±0.09) W m−2 from CO2, 1.08 (± 0.21) W m−2 from other well-mixed greenhouse gases, −1.01 (± 0.23) W m−2 from aerosols and −0.09 (±0.13) W m−2 from land use change. Quoted uncertainties are 1 standard deviation across model best estimates, and 90 % confidence in the reported forcings, due to internal variability, is typically within 0.1 W m−2. The majority of the remaining 0.21 W m−2 is likely to be from ozone. In most cases, the largest contributors to the spread in effective radiative forcing (ERF) is from the instantaneous radiative forcing (IRF) and from cloud responses, particularly aerosol–cloud interactions to aerosol forcing. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the stratospherically adjusted radiative forcing is approximately equal to ERF for greenhouse gas forcing but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol forcing ranges from −0.63 to −1.37 W m−2, exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO2 forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol forcing is uncorrelated with climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol forcing and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol forcing to recreate observed historical warming.},
doi = {10.5194/acp-20-9591-2020},
url = {https://www.osti.gov/biblio/1647673}, journal = {Atmospheric Chemistry and Physics (Online)},
issn = {1680-7324},
number = 16,
volume = 20,
place = {Germany},
year = {Mon Aug 17 00:00:00 EDT 2020},
month = {Mon Aug 17 00:00:00 EDT 2020}
}

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