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Title

On the interpretation of inter-model spread in CMIP5 climate sensitivity estimates

Publication Year

2013

Author(s)
  • Vial, Jessica
  • Dufresne, Jean-Louis
  • Bony, Sandrine
Source
CLIMATE DYNAMICS Volume: 41 Issue: 11-12 Pages: 3339-3362 Published: 2013
ISSN
0930-7575 eISSN: 1432-0894
Abstract

This study diagnoses the climate sensitivity, radiative forcing and climate feedback estimates from eleven general circulation models participating in the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5), and analyzes inter-model differences. This is done by taking into account the fact that the climate response to increased carbon dioxide (CO2) is not necessarily only mediated by surface temperature changes, but can also result from fast land warming and tropospheric adjustments to the CO2 radiative forcing. By considering tropospheric adjustments to CO2 as part of the forcing rather than as feedbacks, and by using the radiative kernels approach, we decompose climate sensitivity estimates in terms of feedbacks and adjustments associated with water vapor, temperature lapse rate, surface albedo and clouds. Cloud adjustment to CO2 is, with one exception, generally positive, and is associated with a reduced strength of the cloud feedback; the multi-model mean cloud feedback is about 33 % weaker. Non-cloud adjustments associated with temperature, water vapor and albedo seem, however, to be better understood as responses to land surface warming. Separating out the tropospheric adjustments does not significantly affect the spread in climate sensitivity estimates, which primarily results from differing climate feedbacks. About 70 % of the spread stems from the cloud feedback, which remains the major source of inter-model spread in climate sensitivity, with a large contribution from the tropics. Differences in tropical cloud feedbacks between low-sensitivity and high-sensitivity models occur over a large range of dynamical regimes, but primarily arise from the regimes associated with a predominance of shallow cumulus and stratocumulus clouds. The combined water vapor plus lapse rate feedback also contributes to the spread of climate sensitivity estimates, with inter-model differences arising primarily from the relative humidity responses throughout the troposphere. Finally, this study points to a substantial role of nonlinearities in the calculation of adjustments and feedbacks for the interpretation of inter-model spread in climate sensitivity estimates. We show that in climate model simulations with large forcing (e.g., 4 x CO2), nonlinearities cannot be assumed minor nor neglected. Having said that, most results presented here are consistent with a number of previous feedback studies, despite the very different nature of the methodologies and all the uncertainties associated with them.

Author Keyword(s)
  • Climate sensitivity
  • Feedback
  • Radiative forcing
  • Fast adjustment
  • Radiative kernel
  • CMIP5 climate model simulations
  • Climate change
  • Inter-model spread
KeyWord(s) Plus
  • RADIATIVE KERNEL TECHNIQUE
  • TROPOSPHERIC ADJUSTMENT
  • FEEDBACK PROCESSES
  • CLOUD FEEDBACK
  • RANGE
  • STATE
ESI Discipline(s)
  • Geosciences
Web of Science Category(ies)
  • Meteorology & Atmospheric Sciences
Adress(es)

[Vial, Jessica; Dufresne, Jean-Louis; Bony, Sandrine] CNRS, Meteorol Dynam Lab, F-75752 Paris 05, France; [Vial, Jessica; Dufresne, Jean-Louis; Bony, Sandrine] Univ Paris 06, F-75752 Paris 05, France

Reprint Adress

Vial, J (reprint author), CNRS, Meteorol Dynam Lab, 4 Pl Jussieu, F-75752 Paris 05, France.

Country(ies)
  • France
CNRS - Adress(es)
  • Laboratoire de météorologie dynamique (LMD), UMR8539
Accession Number
WOS:000327080400029
uid:/7XPC6H1B
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