30‐Year satellite record reveals contrasting Arctic and Antarctic decadal sea ice variability

A 30‐year satellite record of sea ice extents derived mostly from satellite microwave radiometer observations reveals that the Arctic sea ice extent decreased by 0.30 ± 0.03 × 10 6 km 2 /10 yr from 1972 through 2002, but by 0.36 ± 0.05 × 10 6 km 2 /10yr from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast, the Antarctic sea ice extent decreased dramatically over the period 1973–1977, then gradually increased. Over the full 30‐year period, the Antarctic ice extent decreased by 0.15 ± 0.08 × 10 6 km 2 /10 yr. The trend reversal is attributed to a large positive anomaly in Antarctic sea ice extent in the early 1970's, an anomaly that apparently began in the late 1960's, as observed in early visible and infrared satellite images.