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Figure 11. A, Monthly average sea-ice extent in the Northern Hemisphere, November 1978–December 2003. B, Deviations in monthly sea-ice extents in the Northern Hemisphere, November 1978–December 2003. C, Yearly and seasonal average sea-ice extents in the Northern Hemisphere, 1979–2003. Winter is averaged for January–March; spring is averaged for April–June; summer is averaged for July–September; and autumn is averaged for October–December. All values are derived from data from NASA’s Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) and the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSMI). (Updated from Parkinson and others, 1999.)