Arctic sea ice extent minimum remains lower than 30 year average

Arctic sea ice extent reached an annual minimum of 4.64 million square kilometers in September. This is a significant decline compared to the 1981 to 2010 median.  However, the 2017 minimum remains above the 2012 low record extent.  Arctic sea ice extent compared to 30 year meanThe daily sea ice extent is derived from the National Snow and Ice Data Center (NSIDC) Sea Ice Index.  The Sea Ice Index is computed from methods developed by NASA for estimating sea ice conditions using passive-microwave data from the Special Sensor Microwave Imager/Sounder (SSMIS) which is on board Defense Meteorological Satellites.  Sea ice extent is computed by analyzin daily gridded brightness temperatures from orbital swath imagery captured by the Special Sensor Microwave Imager/Sounder and counting areas in the grid with ice concentrations greater than 15% on each day.  The same method to compute the daily Sea Ice Index has been used consistently since 1979. National Snow and Ice Data Center