Who Are You Going To Believe - The Government Climate Scientists Or The Data?
Guest Post Dr David M.W. Evans
We check the main predictions of the climate models against the best and latest data. Fortunately the climate models got all their major predictions wrong. Why? Every serious skeptical scientist has been consistently saying essentially the same thing for over 20 years, yet most people have never heard the message - here it is, put simply enough for any lay reader willing to pay attention.
What the Government Climate Scientists Say
Figure 1: The climate models. If the CO2 level doubles (as it is on course to do by about 2070 to 2100), the climate models estimate the temperature increase due to that extra CO2 will be about 1.1°C × 3 = 3.3°C. 
The direct effect of CO2 is well-established physics, based on laboratory results, and known for over a century.
Feedbacks are due to the ways the Earth reacts to the direct warming effect of the CO2. The threefold amplification by feedbacks is based on the assumption, or guess, made around 1980, that more warming due to CO2 will cause more evaporation from the oceans and that this extra water vapor will in turn lead to even more heat trapping because water vapor is the main greenhouse gas. And extra heat will cause even more evaporation, and so on. This amplification is built into all the climate models. The amount of amplification is estimated by assuming that nearly all the industrial-age warming is due to our CO2.
The government climate scientists and the media often tell us about the direct effect of the CO2, but rarely admit that two thirds of their projected temperature increases are due to amplification by feedbacks. They admit there are discrepancies, and go to great lengths to resolve them (see for example, Thorne, Dessler, Sherwood).
What the Skeptics Say
Figure 2: The skeptic's view. If the CO2 level doubles, skeptics estimates that the temperature increase due to that extra CO2 will be about 1.1°C × 0.5 ˜ 0.6°C.
The serious skeptical scientists have always agreed with the government climate scientists about the direct effect of CO2. The argument is entirely about the feedbacks.
The feedbacks dampen or reduce the direct effect of the extra CO2, cutting it roughly in half. The main feedbacks involve evaporation, water vapor, and clouds. In particular, water vapor condenses into clouds, so extra water vapor due to the direct warming effect of extra CO2 will cause extra clouds, which reflect sunlight back out to space and cool the earth, thereby reducing the overall warming.
There are literally thousands of feedbacks, each of which either reinforces or opposes the direct warming effect of the extra CO2. Almost every long-lived system is governed by net feedback that dampens its response to a perturbation. If a system instead reacts to a perturbation by amplifying it, the system is likely to reach a tipping point and become unstable (like the electronic squeal that erupts when a microphone gets too close to its speakers). The earth's climate is long-lived and stable- it has never gone into runaway greenhouse, unlike Venus - which strongly suggests that the feedbacks dampen temperature perturbations such as that from extra CO2.