Originally Posted by cdcox
The actual model is physical, but the inputs and outputs are statistical in nature.
Actual future CO2 emissions were unknown. So, three statistical representations of future emissions were made: scenarios A, B, and C. Hanson argues that scenario B most closely matched the actual forcing from 1981 to 2006. Austin Chief argues that emissions exceeded those of scenario A (the case where climate forcing was projected to be the greatest). If emissions match scenario B, the Hanson model is pretty reasonable. If emissions exceed scenario A, as Austin Chief is claiming, then the predictions are pretty poor.
One last point about the statistical nature of the output. If you run a climate model from two very similar initial conditions, you will get two different projections of future climate. This is due to the chaotic nature of the physics inside the model. This chaotic behavior is also present in real world climate systems. One can run several climate simulations and determine the ensemble average and variability of future conditions. For the actual measured climate, we can only have one realization. If the actual climate measurements fall within the bounds of the ensemble average and confidence intervals of many simulations, then it can be said that the model describes the climate.
It should be pointed out that in 1988, Hansen didn't have the computing power to make ensemble runs. He could only do one run, which won't necessarily match the earth's climate in an exact manner due to the inherent internal stochasticity of the climate system.
In short...The issue of C02 saturation is firmly disputed. Global warmist's arguements are based on the hypothesis that an '''artfiicially'' high concentration of C02 is what's causing climate change yet faoil to demonstrate it repeattedly, for starters.