Universität zu Köln

Smith, Christopher J., Kramer, Ryan J., Myhre, Gunnar ORCID: 0000-0002-4309-476X, Alterskjaer, Kari ORCID: 0000-0003-4650-1102, Collins, William ORCID: 0000-0002-7419-0850, Sima, Adriana, Boucher, Olivier ORCID: 0000-0003-2328-5769, Dufresne, Jean-Louis ORCID: 0000-0003-4764-9600, Nabat, Pierre, Michou, Martine, Yukimoto, Seiji, Cole, Jason, Paynter, David, Shiogama, Hideo, O'Connor, Fiona M., Robertson, Eddy, Wiltshire, Andy, Andrews, Timothy ORCID: 0000-0002-8248-8753, Hannay, Cecile, Miller, Ron, Nazarenko, Larissa, Kirkevag, Alf, Olivie, Dirk, Fiedler, Stephanie, Lewinschal, Anna, Mackallah, Chloe, Dix, Martin, Pincus, Robert ORCID: 0000-0002-0016-3470 and Forster, Piers M. (2020). Effective radiative forcing and adjustments in CMIP6 models. Atmos. Chem. Phys., 20 (16). S. 9591 - 9619. GOTTINGEN: COPERNICUS GESELLSCHAFT MBH. ISSN 1680-7324

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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) Wm(-2) from CO2, 1.08 (+/- 0.21) Wm(-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 x 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.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Smith, Christopher J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kramer, Ryan J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Myhre, Gunnar UNSPECIFIED orcid.org/0000-0002-4309-476X UNSPECIFIED Alterskjaer, Kari UNSPECIFIED orcid.org/0000-0003-4650-1102 UNSPECIFIED Collins, William UNSPECIFIED orcid.org/0000-0002-7419-0850 UNSPECIFIED Sima, Adriana UNSPECIFIED UNSPECIFIED UNSPECIFIED Boucher, Olivier UNSPECIFIED orcid.org/0000-0003-2328-5769 UNSPECIFIED Dufresne, Jean-Louis UNSPECIFIED orcid.org/0000-0003-4764-9600 UNSPECIFIED Nabat, Pierre UNSPECIFIED UNSPECIFIED UNSPECIFIED Michou, Martine UNSPECIFIED UNSPECIFIED UNSPECIFIED Yukimoto, Seiji UNSPECIFIED UNSPECIFIED UNSPECIFIED Cole, Jason UNSPECIFIED UNSPECIFIED UNSPECIFIED Paynter, David UNSPECIFIED UNSPECIFIED UNSPECIFIED Shiogama, Hideo UNSPECIFIED UNSPECIFIED UNSPECIFIED O'Connor, Fiona M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Robertson, Eddy UNSPECIFIED UNSPECIFIED UNSPECIFIED Wiltshire, Andy UNSPECIFIED UNSPECIFIED UNSPECIFIED Andrews, Timothy UNSPECIFIED orcid.org/0000-0002-8248-8753 UNSPECIFIED Hannay, Cecile UNSPECIFIED UNSPECIFIED UNSPECIFIED Miller, Ron UNSPECIFIED UNSPECIFIED UNSPECIFIED Nazarenko, Larissa UNSPECIFIED UNSPECIFIED UNSPECIFIED Kirkevag, Alf UNSPECIFIED UNSPECIFIED UNSPECIFIED Olivie, Dirk UNSPECIFIED UNSPECIFIED UNSPECIFIED Fiedler, Stephanie UNSPECIFIED UNSPECIFIED UNSPECIFIED Lewinschal, Anna UNSPECIFIED UNSPECIFIED UNSPECIFIED Mackallah, Chloe UNSPECIFIED UNSPECIFIED UNSPECIFIED Dix, Martin UNSPECIFIED UNSPECIFIED UNSPECIFIED Pincus, Robert UNSPECIFIED orcid.org/0000-0002-0016-3470 UNSPECIFIED Forster, Piers M. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-323139
DOI:	10.5194/acp-20-9591-2020
Journal or Publication Title:	Atmos. Chem. Phys.
Volume:	20
Number:	16
Page Range:	S. 9591 - 9619
Date:	2020
Publisher:	COPERNICUS GESELLSCHAFT MBH
Place of Publication:	GOTTINGEN
ISSN:	1680-7324
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language COUPLED MODEL; CLIMATE SENSITIVITY; REACTIVE GASES; EMISSIONS; FEEDBACK; AEROSOLS; SURFACE; CLOUDS; SCENARIOS; PROTOCOL Multiple languages Environmental Sciences; Meteorology & Atmospheric Sciences Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/32313