What does this mean?

The map shows annual minimum exposed snow and ice cover for each of the years of the NASA Earth Observing System era (2000-2013). This product indicates those areas that never reveal complete soil or vegetation cover across a pixel during the particular year. The annual exposed ice is indicated by blue pixels. The resolution of the persistent snow and ice data is higher than the other maps presented here, so changes may be better observed by zooming in, particularly to Alaska. Continue reading...