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Title: Climate Sensitivity of the Community Climate System Model, Version 4

Equilibrium climate sensitivity of the Community Climate System Model Version 4 (CCSM4) is 3.20°C for 1° horizontal resolution in each component. This is about a half degree Celsius higher than in the previous version (CCSM3). The transient climate sensitivity of CCSM4 at 1° resolution is 1.72°C, which is about 0.2°C higher than in CCSM3. These higher climate sensitivities in CCSM4 cannot be explained by the change to a preindustrial baseline climate. We use the radiative kernel technique to show that from CCSM3 to CCSM4, the global mean lapse-rate feedback declines in magnitude, and the shortwave cloud feedback increases. These two warming effects are partially canceled by cooling due to slight decreases in the global mean water-vapor feedback and longwave cloud feedback from CCSM3 to CCSM4. A new formulation of the mixed-layer, slab ocean model in CCSM4 attempts to reproduce the SST and sea ice climatology from an integration with a full-depth ocean, and it is integrated with a dynamic sea ice model. These new features allow an isolation of the influence of ocean dynamical changes on the climate response when comparing integrations with the slab ocean and full-depth ocean. The transient climate response of the full-depth ocean version is 0.54more » of the equilibrium climate sensitivity when estimated with the new slab ocean model version for both CCSM3 and CCSM4. We argue the ratio is the same in both versions because they have about the same zonal mean pattern of change in ocean surface heat flux, which broadly resembles the zonal mean pattern of net feedback strength.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [3] ;  [1] ;  [3] ;  [3]
  1. Univ. of Washington, Seattle, WA (United States)
  2. Oregon State Univ., Corvallis, OR (United States)
  3. National Center for Atmospheric Research, Boulder, CO (United States)
Publication Date:
OSTI Identifier:
1029980
Report Number(s):
DOE/ER64433
Journal ID: ISSN 0894-8755
Grant/Contract Number:
FG02-07ER64433
Type:
Accepted Manuscript
Journal Name:
Journal of Climate
Additional Journal Information:
Journal Volume: 25; Journal Issue: 9; Journal ID: ISSN 0894-8755
Publisher:
American Meteorological Society
Research Org:
University of Washington, Seattle, WA
Sponsoring Org:
USDOE SC Office of Biological and Environmental Research (SC-23)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES Climate sensitivity, Climate change, Ocean Heat Uptake, Climate Feedback