Attention alarmists: the latest version of the world's most widely used climate model arbitrarily increases the fictitious forcing from CO2 'back-radiation' and non-existent positive-feedbacks from clouds by 25%, from a fallacious 3.2C to 4.0C per doubling of CO2.
Journal of Climate 2011 ; e-View doi: 10.1175/JCLI-D-11-00197.1
The Evolution of Climate Sensitivity and Climate Feedbacks in the Community Atmosphere Model
A. Gettelman et al
Abstract: We use the major evolution of the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM) to diagnose climate feedbacks, understand how climate feedbacks change with different physical parameterizations, and identify the processes and regions that determine climate sensitivity. In the evolution of CAM from version 4 to version 5, the water vapor, temperature, surface albedo and lapse rate feedbacks are remarkably stable across changes to the physical parameterization suite. However, the climate sensitivity increases from 3.2K in CAM4 to 4.0K in CAM5. The difference is mostly due to (a) more positive cloud feedbacks and (b) higher CO2 radiative forcing in CAM5. The inter-model differences in cloud feedbacks are largest in the tropical trade cumulus regime and in the mid-latitude storm-tracks. The sub-tropical stratocumulus regions do not contribute strongly to climate feedbacks due to their small area coverage. A “modified Cess” configuration for atmosphere only model experiments is shown to reproduce slab ocean model results. Several parameterizations contribute to changes in tropical cloud feedbacks between CAM4 and CAM5, but the new shallow convection scheme causes the largest mid-latitude feedback differences and the largest change in climate sensitivity. Simulations with higher cloud forcing in the mean state have lower climate sensitivity. This work provides a methodology for further analysis of climate sensitivity across models and a framework for targeted comparisons to observations that can help constrain climate sensitivity to radiative forcing.