Extent of sea ice
Extent of sea ice in September of 1980 (outer red boundary), 1998 (outer pink boundary) and 2012 (outer white boundary). Modified from Perovich and Richter-Menge (2009).
Extent of sea ice (million square kilometers)
Arctic, Observed, NSIDC Sea Ice Index, http://nsidc.org/data/seaice_index/, Sea, Ice
Perovich and Richter-Menge (2009)