NOAA/NMC/CAC Arctic and Antarctic Monthly Sea Ice Extent, 1973-1990, Version 1
Sea ice extent from January 1973 through August 1990 was digitized from weekly operational sea ice charts produced by the Navy/NOAA Joint Ice Center. Charts were digitized by hand using a 1 degree latitude x 2.5 degrees longitude grid.  The grid boxes were then summed in 1 degree latitude  x 10 degrees longitude …