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Title: Quantifying the Sources of Intermodel Spread in Equilibrium Climate Sensitivity

This paper clarifies the causes of intermodel differences in the global-average temperature response to doubled CO 2, commonly known as equilibrium climate sensitivity (ECS). The authors begin by noting several issues with the standard approach for decomposing ECS into a sum of forcing and feedback terms. This leads to a derivation of an alternative method based on linearizing the effect of the net feedback. Consistent with previous studies, the new method identifies shortwave cloud feedback as the dominant source of intermodel spread in ECS. This new approach also reveals that covariances between cloud feedback and forcing, between lapse rate and longwave cloud feedbacks, and between albedo and shortwave cloud feedbacks play an important and previously underappreciated role in determining model differences in ECS. Finally, defining feedbacks based on fixed relative rather than specific humidity (as suggested by Held and Shell) reduces the covariances between processes and leads to more straightforward interpretations of results.
Authors:
 [1] ;  [1] ;  [1] ;  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-670060
Journal ID: ISSN 0894-8755
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Journal of Climate
Additional Journal Information:
Journal Volume: 29; Journal Issue: 2; Journal ID: ISSN 0894-8755
Publisher:
American Meteorological Society
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; physical meteorology and climatology; climate sensitivity; feedback; forcing; mathematical and statistical techniques; statistics; models and modeling; climate models
OSTI Identifier:
1375993

Caldwell, Peter M., Zelinka, Mark D., Taylor, Karl E., and Marvel, Kate. Quantifying the Sources of Intermodel Spread in Equilibrium Climate Sensitivity. United States: N. p., Web. doi:10.1175/JCLI-D-15-0352.1.
Caldwell, Peter M., Zelinka, Mark D., Taylor, Karl E., & Marvel, Kate. Quantifying the Sources of Intermodel Spread in Equilibrium Climate Sensitivity. United States. doi:10.1175/JCLI-D-15-0352.1.
Caldwell, Peter M., Zelinka, Mark D., Taylor, Karl E., and Marvel, Kate. 2016. "Quantifying the Sources of Intermodel Spread in Equilibrium Climate Sensitivity". United States. doi:10.1175/JCLI-D-15-0352.1. https://www.osti.gov/servlets/purl/1375993.
@article{osti_1375993,
title = {Quantifying the Sources of Intermodel Spread in Equilibrium Climate Sensitivity},
author = {Caldwell, Peter M. and Zelinka, Mark D. and Taylor, Karl E. and Marvel, Kate},
abstractNote = {This paper clarifies the causes of intermodel differences in the global-average temperature response to doubled CO2, commonly known as equilibrium climate sensitivity (ECS). The authors begin by noting several issues with the standard approach for decomposing ECS into a sum of forcing and feedback terms. This leads to a derivation of an alternative method based on linearizing the effect of the net feedback. Consistent with previous studies, the new method identifies shortwave cloud feedback as the dominant source of intermodel spread in ECS. This new approach also reveals that covariances between cloud feedback and forcing, between lapse rate and longwave cloud feedbacks, and between albedo and shortwave cloud feedbacks play an important and previously underappreciated role in determining model differences in ECS. Finally, defining feedbacks based on fixed relative rather than specific humidity (as suggested by Held and Shell) reduces the covariances between processes and leads to more straightforward interpretations of results.},
doi = {10.1175/JCLI-D-15-0352.1},
journal = {Journal of Climate},
number = 2,
volume = 29,
place = {United States},
year = {2016},
month = {1}
}