On Muller | Climate Skeptic

3. CO2 certainly has an effect on temperatures, but so do a lot of other things. The science that CO2 warms the Earth is solid. The science that CO2 catastrophically warms the Earth, with a high positive feedback climate system driven to climate sensitivities to CO2 of 3C per doubling or higher is not solid. Assuming half of past warming is due to man’s CO2 is not enough to support catastrophic forecasts. If half of past warming, or about .4C is due to man, that means climate sensitivity is around 1C, exactly the no-feedback number that climate skeptics have thought it was near for years. So additional past man-made warming has to be manufactured somehow to support the higher sensitivity, positive feedback cases.