On the Arctic climate paradox and the continuing role of atmospheric circulation in affecting sea ice conditions

The reduction in ice cover observed in the late 1980s and early 1990s has been attributed to the strongly positive Arctic Oscillation (AO) phase during that time. However, despite a change in the AO to more neutral conditions since then, ice extent and the fraction of old ice have continued to decrease. This mismatch between the AO index and loss of ice can be explained by the frequency of three main sea level pressure (SLP) patterns that yield overall variability in SLP, rather than the presence of a single, coherent physical pattern of SLP reduction associated with the positive mode of the AO. These three patterns were in phase during the peak AO period but their frequency has varied differently since then, with two of the patterns continuing to contribute to reduced ice cover in the western Arctic. Hence, regional atmospheric circulation remains a significant factor in recent reductions in ice cover.