What does this mean?

The maps and bar graphs show how the Arctic Ocean sea ice cover for different years and months compares to averages from 1979 to 2013. The maps show spatial patterns of the differences (anomalies) of sea ice concentration for each year and month. Sea ice concentration is the fraction of the ocean covered by sea ice and is expressed as a percentage. The bar graphs show anomalies of sea ice extent for the Northern Hemisphere as a whole. Sea ice extent represents all areas with at least a 15% ice concentration. The bar graphs of sea ice extent and the maps of ice concentration anomalies are based on the same data as used in the NSIDC Sea Ice Index. Continue reading...