The Arctic climate paradox: The recent decrease of the Arctic Oscillation

A current paradox is that many physical and biological indicators of Arctic change-summer sea-ice extent, spring surface air temperature and cloud cover, and shifts in vegetation and other ecosystems-show nearly linear trends over the previous two and a half decades, while the Arctic Oscillation, a representative atmospheric circulation index often associated with Arctic change, has had a different, more episodic behavior, with a near-neutral or negative phase for 6 of the last 9 years (1996-2004) following a positive phase (1989-1995). Stratospheric temperature anomalies over the Arctic, which serve as an index of the strength of the polar vortex, also show this episodic character. Model projections of Arctic temperature for 2010-2029 show model-to-model and region-to-region differences suggesting large variability in the future response of atmospheric circulation to external forcing. Thus internal processes in the western Arctic may have a larger role in shaping the present persistence of Arctic change than has been previously recognized.