by Tracy Rogers
4-21-14
UAF Phys 212
Arctic Sea Ice
Extent
Sea ice extent
(SIE) measures the amount of ice coverage in the Arctic
Ocean. SIE is important for several reasons, most notably
the heat absorbed from the sun during summer months. Ice
has a very high albedo (reflectivity), which means that
rather than absorb energy from the sun, it deflects it.
Ocean water, however, has a very low albedo. As ice melts,
the Arctic Ocean absorbs more energy from the sun, and
then the ice melts faster. Since the Arctic has 24 hours
of sunlight a day in the summer, the coverage of ice has a
significant impact on the amount of energy absorbed from
the sun during those months.
The most common method for measuring SIE across the Arctic
is through satellite remote sensing, and much of the data
gathering and analysis is completed by NASA
and NSIDC. SIE is
calculated from a concentration map by adding up the area
of all pixels with a concentration of 30 percent or more
sea ice.
Between 1979
and 2011, summer trends in sea ice extent trended steadily
downward, while March SIE remained relatively stable:
September SIE is represented by the thick black line and thin regression line.
March SIE is represented by the thick blue line and thin regression line.
September had a mean of 6.2 and standard deviation 1.05 106 km2. Except for 2009, 2007 through 2013 were all at least one standard deviation below the mean. 2007 and 2012 were both over two standard deviations below the mean.