On August 26, 2012, the National Snow and Ice Data Center (NSIDC) reported that the areal extent of sea ice cover in the Artic reached a new satellite-measured low of 4.10 million square kilometers (1.58 million square miles). On September 5, they reported that sea ice extent fell below 4 million square kilometers (1.52 million square miles). Melting of northern hemisphere sea ice may impact many aspects of Arctic weather, wildlife, and resource development opportunities. In addition, the declining trend of sea ice my influence the longevity of land ice as well, which has a strong connection to global sea level.
Sea ice concentration data from October 26, 1978 to the present is available directly from AOOS. These data are calculated from measurements taken by a series of satellites including the Nimbus satellites’ Scanning Multichannel Microwave Radiometers(SMMR) the Defense Meteorological Satellite Program (DMSP) satellites’ Special Sensor Microwave Imagers/Sounders (SSMIS). The instruments measure passive microwave radiation emitted from sea ice, which is relatively unaffected by cloud-cover. Data over the pole is not present because the satellites are in near-polar, sun-synchronous orbits, never passing directly over the North pole.
Below is an animation that compares sea ice concentration data from 1990, 1995, 2000, and 2012, showing the dramatic changes in sea ice that has occurred in the past few decades.