Arctic sea ice extents, areas, and trends, 1978-1996

Satellite passive-microwave data for November 1978 through December 1996 re veal marked seasonal, regional, and interannual variabilities, with an over all decreasing trend of -34,300 +/- 3700 km(2)/yr (-2.8%/decade) in Arctic sea ice extents over the 18.2-year period. Decreases occur in all seasons a nd on a yearly average basis, although they are largest in spring and small est in autumn. Regionally, the Kara and Barents Seas have the largest decre ases, at -15,200 +/- 1900 km2(/)yr (-10.5%/decade), followed by the Seas of Okhotsk and Japan, the Arctic Ocean, Greenland Sea, Hudson Bay, and Canadi an Archipelago. The yearly average trends for the total, the Kara and Baren ts Seas, and the Seas of Okhotsk and Japan all have high statistical signif icance, with the null hypothesis of a 0 slope being rejected at a 99% confi dence level. Regions showing increasing yearly average ice extents are Baff in Bay/Labrador Sea, the Gulf of St. Lawrence, and the Bering Sea, with onl y the increases in the Gulf of St. Lawrence being statistically significant at the 99% level. Hemispheric results for sea ice areas exhibit the same - 2.8%/decade decrease as for ice extents and hence a lower absolute decrease (-29,500 +/- 3800 km(2)/yr), with the ice-free area within the ice pack co rrespondingly decreasing at -4800 +/- 1600 km(2)/yr. Confidence levels for the trends in ice areas and ice-free water areas exceed 99% and 95%, respec tively. Nonetheless, interannual variability is high, and, for instance, th e Arctic Ocean ice extents have a positive trend 1990-1996, in spite of the ir negative trend for the time period as a whole.