Arctic Sea Ice Extent
1. Sea ice extent is a measure of the surface area of the ocean covered by sea ice. Increases in air and ocean temperatures decrease sea ice extent; in turn, the resulting darker ocean surface absorbs more solar radiation and increases Arctic warming.
2.The minimum sea ice extent in the Arctic, measured in September of each year, has decreased by about 32% since 1979.
Sea ice extent is estimated using daily satellite images to calculate the total ocean area that has an ice concentration of 15% or more. Trends in sea ice extent are calculated from average values measured during the month of September, which is typically when sea ice extent reaches its annual minimum. Minimum sea ice extent in the Arctic has decreased by about 32% since 1979 (the first full year of satellite data). At this rate, some projections suggest that the Arctic will be virtually ice-free during summers by the middle of this century.