Paper in Press
GEOPHYSICAL RESEARCH LETTERS, doi:10.1029/2012GL051607
Forcing, Feedbacks and Climate Sensitivity in CMIP5 Coupled Atmosphere-Ocean Climate Models
- Range of eqm climate sensitivity (2.1-4.7K) is similar to that found in CMIP3.
- Differences in cloud feedbacks continue to be a large source of this uncertainty.
- Some models show small deviations from linear behaviour.
We quantify forcing and feedbacks across available CMIP5 coupled atmosphere-ocean general circulation models (AOGCMs) by analysing simulations forced by an abrupt quadrupling of atmospheric carbon dioxide concentration. This is the first application of the linear forcing-feedback regression analysis of Gregory et al. (2004) to an ensemble of AOGCMs. The range of equilibrium climate sensitivity is 2.1 - 4.7 K. Differences in cloud feedbacks continue to be important contributors to this range. Some models show small deviations from a linear dependence of top-of-atmosphere radiative fluxes on global surface temperature change. We show that this phenomenon largely arises from shortwave cloud radiative effects over the ocean and is consistent with independent estimates of forcing using fixed sea-surface temperature methods. We suggest that future research should focus more on understanding transient climate change, including any time-scale dependence of the forcing and/or feedback, rather than on the equilibrium response to large instantaneous forcing.
Received 6 March 2012; accepted 11 April 2012.
Citation: (2012), Forcing, Feedbacks and Climate Sensitivity in CMIP5 Coupled Atmosphere-Ocean Climate Models, Geophys. Res. Lett., doi:10.1029/2012GL051607, in press.