What was done
Satellite-derived data of sea-ice extent (defined as the total area of all grid cells having at least 15% sea-ice coverage) were used to calculate Arctic sea-ice extent trends for the periods 1979-1990 and 1990-1999.

What was learned
Since the late 1970s, there has been a well-documented decline in Arctic sea-ice extent, which many people have attributed to global warming.  However, in seven of the nine regions into which the Arctic was divided for the analyses of this study, it was found that "the sign of the trend reversed from the 1979-1990 period to the 1990-1999 period," with the several reversals occurring about the time the North Atlantic Oscillation (NAO) "reached a peak in its annual index."

What it means
Parkinson reports that "several studies have revealed possible long-term oscillatory behavior of one type or another in the Arctic sea ice cover," including "connections with: (1) the North Atlantic Oscillation (e.g., Hurrell and van Loon, 1997; Johannessen et al., 1999; Kwok and Rothrock, 1999; Deser et al., 2000; Kwok, 2000, Vinje, 2001) and the spatially broader Arctic Oscillation (e.g., Deser et al., 2000; Wang and Ikeda, 2000); (2) the Arctic Ocean Oscillation (Polyakov et al., 1999; Proshutinsky et al., 1999); (3) a "see-saw" in winter temperatures between Greenland and northern Europe (Rogers and van Loon, 1979); and (4) an interdecadal Arctic climate cycle (Mysak et al., 1990; Mysak and Power, 1992)."

These findings, together with those of the current study, suggest, in the words of Parkinson, "the possibility of close connections between the sea ice cover and major oscillatory patterns in the atmosphere and oceans," which observation, she says, "provides a strong rationale for considerable caution when extrapolating into the future the widely reported decreases in the Arctic ice cover over the past few decades or when attributing the decreases primarily to global warming."

References
Deser, C., Walsh, J. and Timlin, M.S.  2000.  Arctic sea ice variability in the context of recent atmospheric circulation trends.  Journal of Climate 13: 617-633.

Hurrell, J.W. and van Loon, H.  1997.  Decadal variations in climate associated with the North Atlantic Oscillation.  Climatic Change 36: 301-326.

Johannessen, O.M., Shalina, E.V. and Miles, M.W.  1999.  Satellite evidence for an Arctic sea ice cover in transformation.  Science 286: 1937-1939.

Kwok, R.  2000.  Recent changes in Arctic Ocean sea ice motion associated with the North Atlantic Oscillation.  Geophysical Research Letters 27: 775-778.

Kwok, R. and Rothrock, D.A.  1999.  Variability of Fram Strait ice flux and North Atlantic Oscillation.  Journal of Geophysical Research 104: 5177-5189.

Mysak, L.A., Manak, D.K. and Marsden, R.F.  1990.  Sea-ice anomalies observed in the Greenland and Labrador Seas during 1901-1984 and their relation to an interdecadal Arctic climate cycle.  Climate Dynamics 5: 111-133.

Mysak, L.A. and Power, S.B.  1992.  Sea-ice anomalies in the western Arctic and Greenland-Iceland Sea and their relation to an interdecadal climate cycle.  Climatological Bulletin/Bulletin Climatologique 26: 147-176.

Polyakov, I.V., Proshutinsky, A.Y. and Johnson, M.A.  1999.  Seasonal cycles in two regimes of Arctic climate.  Journal of Geophysical Research 104: 25,761-25,788.

Proshutinsky, A.Y., Polyakov, I.V. and Johnson, M.A.  1999.  Climate states and variability of Arctic ice and water dynamics during 1946-1997.  Polar Research 18: 135-142.

Rogers, J.C. and van Loon, H.  1979.  The seesaw in winter temperatures between Greenland and Northern Europe.  Part II: Some oceanic and atmospheric effects in middle and high latitudes.  Monthly Weather Review 107: 509-519.

Vinje, T.  2001.  Anomalies and trends of sea ice extent and atmospheric circulation in the Nordic Seas during the period 1864-1998.  Journal of Climate 14: 255-267.

Wang, J. and Ikeda, M.  2000.  Arctic Oscillation and Arctic Sea-Ice Oscillation.  Geophysical Research Letters 27: 1287-1290.