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

[1] 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.