6.9.2. Greenhouse Feedbacks
GCMs have estimated the CO2 doubling temperature change in the absence of feedback processes to be approximately 1.2�C. The existence of feedback loops within the climate system results in a climate sensitivity of 1.5�C to 4.5�C, and makes an otherwise linear association between radiative forcing and global temperature distinctly non-linear. Three of the most important direct climatic feedbacks to greenhouse forcing include the water vapour feedback, the cloud feedback and the ice-albedo feedback. (See also section 2.7).