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

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 CO 2 forcing simulated by global climate models (GCMs). In this paper, 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. Finally, the causes of intermodel spread in cloud feedback aremore » discussed, focusing particularly on the 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. Univ. of Reading (United Kingdom). Dept. of Meteorology
  2. Meteo-France, Toulouse (France). National Center for Meteorological Research (CNRM)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Cloud Processes Research Group
  4. Univ. of Washington, Seattle, WA (United States). Dept. of Atmospheric Sciences
Publication Date:
Report Number(s):
LLNL-JRNL-707398
Journal ID: ISSN 1757-7780
Grant/Contract Number:
AC52-07NA27344; SC0012580; NNH14AX83I
Type:
Accepted Manuscript
Journal Name:
Wiley Interdisciplinary Reviews: Climate Change
Additional Journal Information:
Journal Volume: 8; Journal Issue: 4; Journal ID: ISSN 1757-7780
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Univ. of Washington, Seattle, WA (United States); Univ. of Reading (United Kingdom)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Aeronautic and Space Administration (NASA); European Research Council (ERC)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES
OSTI Identifier:
1357404

Ceppi, Paulo, Brient, Florent, Zelinka, Mark D., and Hartmann, Dennis L.. Cloud feedback mechanisms and their representation in global climate models. United States: N. p., 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. 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". United States. doi:10.1002/wcc.465. https://www.osti.gov/servlets/purl/1357404.
@article{osti_1357404,
title = {Cloud feedback mechanisms and their representation in global climate models},
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). In this paper, 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. Finally, 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}
}