Natural climate variability is organized into spatial patterns of high and low pressure regions, represented by the Arctic Oscillation (also called the Northern Annular Mode) and North Pacific patterns in the Northern Hemisphere, and the Southern Annular Mode in the Southern Hemisphere. The patterns of surface temperature anomalies when the Arctic Oscillation and Northern Pacific patterns are in their positive extreme are shown in this figure - as anomalies averaged over periods with different types of dominating pattern of natural variability. When either of the patterns is in its positive extreme, the pattern contributes to an overall Arctic warm period. In recent years (2000–2005), however, the pattern of warm temperature anomalies is circumpolar in distribution and different from either of the two major 20th century climate patterns.
From collection: Global Outlook for Ice and Snow
Hugo Ahlenius, UNEP/GRID-Arendal