Changes in the Arctic Oscillation under increased atmospheric greenhouse gases

Abstract

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 at the late 20th century level, for November to March. The change in the linear AO pattern as GHG increased reveals positive sea level pressure (SLP) anomalies 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 from a quadratic relation to the AO index. This quadratic AO pattern itself has positive SLP anomalies receding from Europe but strengthening over the Gulf of Alaska and surrounding areas as GHG increased. This study points to the importance of the nonlinear structure in determining how the linear oscillatory pattern changes when there is a change in the mean climate.