A group of twelve IPCC fourth assessment report (AR4) climate models have Arctic (60N--90N) warmings that are, on average, 1.9 times greater than their global warmings at the time of CO2 doubling in 1%/year CO2 increase experiments. Forcings and feedbacks that impact the warming response are estimated for both Arctic and global regions based on standard model diagnostics. Fitting a zero-dimensional energy balance model to each region, an expression is derived that gives the Arctic amplification as a function of these forcings and feedbacks. Contributing to Arctic amplification are the Arctic-global differences in surface albedo feedback (SAF), longwave feedback and the net top-of-atmosphere flux forcing (the sum of the surface flux and the atmospheric heat transport convergence). The doubled CO2 forcing and non-SAF shortwave feedback oppose Arctic amplification. SAF is shown to be a contributing, but not a dominating, factor in the simulated Arctic amplification and its intermodel variation.