Antarctic sea ice variability and trends, 1979–2006

Analyses of 28 years (1979–2006) of Antarctic sea ice extents and areas derived from satellite passive microwave radiometers are presented and placed in the context of results obtained previously for the 20‐year period 1979–1998. We present monthly averaged sea ice extents and areas, monthly deviations, yearly and seasonal averages, and their trends for the Southern Hemisphere as a whole and for each of five sectors: the Weddell Sea, the Indian Ocean, the western Pacific Ocean, the Ross Sea, and the Bellingshausen/Amundsen seas. The total Antarctic sea ice extent trend increased slightly, from 0.96 ± 0.61% decade −1 to 1.0 ± 0.4% decade −1 , from the 20‐ to 28‐year period, reflecting contrasting changes in the sector trends. The eight additional years resulted in smaller positive yearly trends in sea ice extent for the Weddell Sea (0.80 ± 1.4% decade −1 ), the western Pacific Ocean (1.4 ± 1.9% decade −1 ), and the Ross Sea (4.4 ± 1.7% decade −1 ) sectors, a lessening of the negative trend for the Bellingshausen/Amundsen seas (−5.4 ± 1.9% decade −1 ) sector, and a shift from a negative trend to a positive trend for the Indian Ocean (1.9 ± 1.4% decade −1 ) sector. The trends for the Southern Hemisphere as a whole and for the Ross Sea sector are significant at the 95% level, whereas the trend for the Bellingshausen/Amundsen seas sector is significant at the 99% level. A similar pattern of yearly trend changes for the two periods is also apparent in the sea ice area time series.