The Arctic Oscillation (AO) under increased atmospheric concentration of greenhouse gases (GHG) was studied by comparing an ensemble of simulations from 13 coupled general circulation models with GHG at the pre-industrial level and and at the level of the late 20th century, for November to March. The change in the AO pattern as GHG increased reveals positive sea level pressure (SLP) anomalies over the Pacific-West Coast centered over the Gulf of Alaska, and weaker negative SLP anomalies over eastern Canada and North Atlantic -- a pattern resembling the nonlinear AO pattern arising mainly from a quadratic relation to the AO index. The nonlinear AO pattern itself has positive SLP anomalies receding from Europe but strengthening over the Pacific-West Coast as GHG increased.