The Sea Ice Index provides a quick look at sea ice changes in spatial and historical context and gives a consistent, up-to-date source of sea ice extent and sea ice concentration values and images. The NSIDC Near-Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations and the Sea Ice Concentrations from Nimbus-7 SSMR and DMSP SSM/I Passive Microwave Data data sets are used to generate the monthly records of sea ice extent and sea ice concentration for the Arctic and Antarctica from satellite passive microwave data.
Data files tabulate monthly mean extent and area, in millions of square kilometers, by year for a given month. Plots of monthly sea ice extent anomalies with trend lines and significance intervals are available. Monthly images show sea ice extent (with an outline of the median extent for that month for comparison), sea ice concentration, trends in sea ice concentration, and anomalies in sea ice concentration. Anomalies and median extent are calculated using a reference period of 1979 through 2000.