Variations in the Arctic, Antarctic, and global sea ice covers during 1978–1987 as observed with the Nimbus 7 scanning multichannel microwave radiometer

The extent and area of sea ice and the amount of open water within the ice boundaries have been computed for the Arctic, Antarctic, and global ice covers every 2 days from November 1978 to August 1987 utilizing the Nimbus 7 scanning multichannel microwave radiometer (SMMR) observations. During this 9‐year period, no significant trends were found in the ice areas of the Arctic and Antarctic packs or in their sum, the global ice area. Also, no significant trends were found in the maxima and minima of the annual ice extents for either polar pack. However, during these 9 years, significant negative trends were found in the annual global ice extent maxima (5%) and in the annual maxima of the global open water area within the sea ice boundaries (7–14%). Significant negative trends were also found in the annual open water maxima in the Antarctic (5–10%) and the annual open water minima in the Arctic (13–23%). The open water within the ice boundaries averaged approximately 14% in the Arctic and 18% in the Antarctic, at the time of their maximum extents. This negative trend in the global ice extent maxima during 1978–1987 also occurred during 1973–1976, found by an analysis of the monochromatic microwave observations obtained by the Nimbus 5 satellite. The combined 15‐year negative trend is 6%. A significant change between the 1973–1976 and the 1978–1987 periods in the Antarctic ice pack is that the very large polynya that formed and persisted in the Weddell Sea during three out of four of the austral winters in the earlier period did not form in any of the 9 years of the latter period. This study, in conjunction with recent studies of global temperature change, lends support to the thesis that climatic changes in the global average temperature might be detectable by observing variations in global sea ice extent.