A comparison of climate feedbacks in general circulation models

A comparison is performed for water vapour, cloud, albedo and lapse rate feedbacks taken from published results of 'offline' feedback calculations for general circulation models (GCMs) with mixed layer oceans performing 2 x CO2 and solar perturbation experiments. All feedbacks show substantial inter-model spread. The impact of uncertainties in feedbacks on climate sensitivity is discussed. A negative correlation is found between water vapour and lapse rate feedbacks, and also between longwave and shortwave components of the cloud feedback. The mean values of the feedbacks are compared with results derived from model inter-comparisons which evaluated cloud forcing derived feedbacks under idealized climate forcing. Results are found to be comparable between the two approaches, after allowing for differences in experimental technique and diagnostic method. Recommendations are made for the future reporting of climate feedbacks.