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Contributions of Different Cloud Types to Feedbacks and Rapid Adjustments in CMIP5*

Journal Article · · Journal of Climate
 [1];  [1];  [1];  [2];  [2];  [3];  [4]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Program for Climate Model Diagnosis and Intercomparison
  2. Met Office Hadley Center, Exeter (United Kingdom)
  3. Univ. of Reading, Exeter (United Kingdom). National Center for Atmospheric Science
  4. Univ. of Leeds (United Kingdom)
+ Show Author Affiliations
When using five climate model simulations of the response to an abrupt quadrupling of CO2, the authors perform the first simultaneous model intercomparison of cloud feedbacks and rapid radiative adjustments with cloud masking effects removed, partitioned among changes in cloud types and gross cloud properties. After CO2 quadrupling, clouds exhibit a rapid reduction in fractional coverage, cloud-top pressure, and optical depth, with each contributing equally to a 1.1 W m-2 net cloud radiative adjustment, primarily from shortwave radiation. Rapid reductions in midlevel clouds and optically thick clouds are important in reducing planetary albedo in every model. As the planet warms, clouds become fewer, higher, and thicker, and global mean net cloud feedback is positive in all but one model and results primarily from increased trapping of longwave radiation. As was true for earlier models, high cloud changes are the largest contributor to intermodel spread in longwave and shortwave cloud feedbacks, but low cloud changes are the largest contributor to the mean and spread in net cloud feedback. The importance of the negative optical depth feedback relative to the amount feedback at high latitudes is even more marked than in earlier models. Furthermore, the authors show that the negative longwave cloud adjustment inferred in previous studies is primarily caused by a 1.3 W m-2 cloud masking of CO2 forcing. Properly accounting for cloud masking increases net cloud feedback by 0.3 W m-2 K-1, whereas accounting for rapid adjustments reduces by 0.14 W m-2 K-1 the ensemble mean net cloud feedback through a combination of smaller positive cloud amount and altitude feedbacks and larger negative optical depth feedbacks.
Research Organization:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
DOE Contract Number:
AC52-07NA27344
OSTI ID:
1226930
Report Number(s):
LLNL-JRNL--567978
Journal Information:
Journal of Climate, Journal Name: Journal of Climate Journal Issue: 14 Vol. 26; ISSN 0894-8755
Publisher:
American Meteorological Society
Country of Publication:
United States
Language:
English

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Related Subjects

58 GEOSCIENCES
climate change
climate models
cloud radiative effects
clouds
feedback
radiation budgets