The "bias" is a natural result of the model. The design of a model is such that the known data is used to create a relationship between the various components. There is no other way to create a model. Whether the model is very simple or very complicated, the design is the same. The computer simply does many very fast calculations based solely on what it has been told to do. Any other explanantion of model design is merely gilding the lilly. Equally whether the model compares two datasets or many, the basic structure is the same. To design a model to look at engineering, we take factors like metal density, thermal expansion, loadings etc. We can then produce a model that allows us to simulate the item we are intending to manufacture, and will show us what the structure will do under varying conditions. If we give the model enough data it will tell us wether the materials and design are suitable or will fail, weigh too much or whatever. However this model is based on actual known data - the mass of metal, the specific heat capacity, the stress caused by loading etc. All these components are known and measured, and their interactions are well understood outside of the model.

In the case of the AGW model, however, we have no proof of the relationships. We create a model by saying that (in the most basic form) the temperature has increased at the same time as the levels of CO2 have increased. We then check that model by asking it what the temperature would be when the CO2 level is X (which we told it in the first place) and then use that as proof of the models efficacy. To make matters worse, we then use "increasing variability" as an outcome. Lets be honest, increasing variability incorporates anything and everything!

However, moving away from models for a moment, I had another thought. The theory is that we are creating all this CO2 which is heating the planet. Now it occurred to me that all the fossil fuel being burnt is being used for many things, but eventually all that energy is being turned to heat because heat is almost always the net result of using power. There may be some light created, but when it has stopped bouncing off the walls it becomes heat. When the car has reached the top of the hill (chemical energy to potential energy) and the brakes are used on the way down they slow the car by converting its kinetic energy to heat. So eventually, all that fossil fuel creates heat.

How much heat? According to Wiki we are producing 21.3billion tonnes CO2 per year. According to Wiki the Earths atmosphere weighs 5x10^18kg and air has a specific heat capacity of about 1.01j/g/K. The eficiency of the various uses of fossil fuel varies, but on average it seems to produce about .5kg of CO2 to make 1kWh of power. A kWh is 1000 watts for an hour, and a watt is a joule per second.

I am not going to type the figures, as they are very long!

So, 21.3billion tonnes of CO2 x 1000 (to get to kg) / 0.5 (kg/kWh) gives us the number of kWh produced each year.

5x10^18 x 1000 = mass of the atmosphere in grams

kWh per year (from calculation above) * 1000 (to get to watts) * 60 (minutes) x 60 (seconds) = joules of energy produced per year.

Finally;

joules of energy per year divided by (mass of atmosphere x specific heat capacity) = 0.03degrees

So if we assume that we are indeed converting chemical energy (fossil fuels) to other forms, and that the majority of that energy ends up as heat, then we are creating enough heat to warm the atmosphere by 0.03 degrees PER YEAR. So in 10 years we would warm the atmosphere by 0.03 x 10 = 0.3 degrees.

Al Gore tells us that we have in fact heated the planet by 0.5 degrees in 100 years. Now I haven't done the calculations to total up the heat energy produced in the last 100 years, but if it currently is 0.03 degrees a year I'd guess that 0.5 degrees in 100 years wouldn't be out of the question?

So maybe the CO2 has done nothing, and we've heated the planet directly? If the CO2 has been responsible for the temperature rise, where has the directly produced energy gone? Hmmm, maybe I should design a model!!