National Geographic is having to redraw the ice cover of the Arctic in its new Atlas of the World because it has changed so much in past years. The boundaries of the ice sheet are calculated by looking at what part of the cover survives for two summers. Those borders used to be fairly stable, but not anymore. The Atlas map-makers are calling this the biggest change that they had to make since the breakup of the U.S.S.R.!
See for yourself on this video produced by the National Snow and Ice Data Center (NSIDC) with NASA data:You can really see the pace accelerate in the latter years, with the multi-year ice cover shrinking significantly.