The most visible change in the Arctic region in recent years has been the rapid decline of the perennial ice cover. The perennial ice is the portion of the sea ice floating on the surface of the ocean that survives the summer. This ice that spans multiple years represents the thickest component of the sea ice cover.
This visualization shows the perennial Arctic sea ice from 1980 to 2012. This is not the sea ice minimum, which occurs in September each year. This measures the perennial sea ice that survives the summer and thus exists for longer than a one-year time span. The measurement for this sea ice was taken during the months of November, December and January each year. The date assigned to the data point is the year of the last measurement (January). The grey disk at the North Pole indicates the region where no satellite data is collected. A graph overlay shows the area's size measured in million square kilometers for each year. The '1980','2008', and '2012' data points are highlighted on the graph.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 126.96.36.199.0