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Title: Cloud feedback mechanisms and their representation in global climate models: Cloud feedback mechanisms and their representation in GCMs

Abstract

Cloud feedback—the change in top-of-atmosphere radiative flux resulting from the cloud response to warming—constitutes by far the largest source of uncertainty in the climate response to CO2 forcing simulated by global climate models (GCMs). We review the main mechanisms for cloud feedbacks, and discuss their representation in climate models and the sources of intermodel spread. Global-mean cloud feedback in GCMs results from three main effects: (1) rising free-tropospheric clouds (a positive longwave effect); (2) decreasing tropical low cloud amount (a positive shortwave [SW] effect); (3) increasing high-latitude low cloud optical depth (a negative SW effect). These cloud responses simulated by GCMs are qualitatively supported by theory, high-resolution modeling, and observations. Rising high clouds are consistent with the fixed anvil temperature (FAT) hypothesis, whereby enhanced upper-tropospheric radiative cooling causes anvil cloud tops to remain at a nearly fixed temperature as the atmosphere warms. Tropical low cloud amount decreases are driven by a delicate balance between the effects of vertical turbulent fluxes, radiative cooling, large-scale subsidence, and lower-tropospheric stability on the boundary-layer moisture budget. High-latitude low cloud optical depth increases are dominated by phase changes in mixed-phase clouds. The causes of intermodel spread in cloud feedback are discussed, focusing particularly on themore » role of unresolved parameterized processes such as cloud microphysics, turbulence, and convection.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4]
  1. Department of Meteorology, University of Reading, Reading UK
  2. Centre National de Recherches M?t?orologiques, M?t?o-France/CNRS, Toulouse France
  3. Cloud Processes Research Group, Lawrence Livermore National Laboratory, Livermore CA USA
  4. Department of Atmospheric Sciences, University of Washington, Seattle WA USA
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1357404
Report Number(s):
LLNL-JRNL-707398
Journal ID: ISSN 1757-7780
Grant/Contract Number:
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Wiley Interdisciplinary Reviews: Climate Change
Additional Journal Information:
Journal Volume: 8; Journal Issue: 4; Journal ID: ISSN 1757-7780
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

Ceppi, Paulo, Brient, Florent, Zelinka, Mark D., and Hartmann, Dennis L.. Cloud feedback mechanisms and their representation in global climate models: Cloud feedback mechanisms and their representation in GCMs. United States: N. p., 2017. Web. doi:10.1002/wcc.465.
Ceppi, Paulo, Brient, Florent, Zelinka, Mark D., & Hartmann, Dennis L.. Cloud feedback mechanisms and their representation in global climate models: Cloud feedback mechanisms and their representation in GCMs. United States. doi:10.1002/wcc.465.
Ceppi, Paulo, Brient, Florent, Zelinka, Mark D., and Hartmann, Dennis L.. 2017. "Cloud feedback mechanisms and their representation in global climate models: Cloud feedback mechanisms and their representation in GCMs". United States. doi:10.1002/wcc.465.
@article{osti_1357404,
title = {Cloud feedback mechanisms and their representation in global climate models: Cloud feedback mechanisms and their representation in GCMs},
author = {Ceppi, Paulo and Brient, Florent and Zelinka, Mark D. and Hartmann, Dennis L.},
abstractNote = {Cloud feedback—the change in top-of-atmosphere radiative flux resulting from the cloud response to warming—constitutes by far the largest source of uncertainty in the climate response to CO2 forcing simulated by global climate models (GCMs). We review the main mechanisms for cloud feedbacks, and discuss their representation in climate models and the sources of intermodel spread. Global-mean cloud feedback in GCMs results from three main effects: (1) rising free-tropospheric clouds (a positive longwave effect); (2) decreasing tropical low cloud amount (a positive shortwave [SW] effect); (3) increasing high-latitude low cloud optical depth (a negative SW effect). These cloud responses simulated by GCMs are qualitatively supported by theory, high-resolution modeling, and observations. Rising high clouds are consistent with the fixed anvil temperature (FAT) hypothesis, whereby enhanced upper-tropospheric radiative cooling causes anvil cloud tops to remain at a nearly fixed temperature as the atmosphere warms. Tropical low cloud amount decreases are driven by a delicate balance between the effects of vertical turbulent fluxes, radiative cooling, large-scale subsidence, and lower-tropospheric stability on the boundary-layer moisture budget. High-latitude low cloud optical depth increases are dominated by phase changes in mixed-phase clouds. The causes of intermodel spread in cloud feedback are discussed, focusing particularly on the role of unresolved parameterized processes such as cloud microphysics, turbulence, and convection.},
doi = {10.1002/wcc.465},
journal = {Wiley Interdisciplinary Reviews: Climate Change},
number = 4,
volume = 8,
place = {United States},
year = 2017,
month = 5
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on May 11, 2018
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