Aug 26, 2002 – While recent studies have shown that on the whole Arctic sea ice has decreased since the late 1970s, satellite records of sea ice around Antarctica reveal an overall increase in the southern hemisphere ice over the same period.
Continued decreases or increases could have substantial impacts on polar climates, because sea ice spreads over a vast area, reflects solar radiation away from the Earth’s surface, and insulates the oceans from the atmosphere.
In a study just published in the Annals of Glaciology, Claire Parkinson of NASA’s Goddard Space Flight Centre analysed the length of the sea ice season throughout the Southern Ocean to obtain trends in sea ice coverage.
Parkinson examined 21 years (1979-1999) of Antarctic sea ice satellite records and discovered that, on average, the area where southern sea ice seasons have lengthened by at least one day per year is roughly twice as large as the area where sea ice seasons have shortened by at least one day per year. One day per year equals three weeks over the 21-year period.
The length of the sea ice season in any particular region or area refers to the number of days per year when at least 15 percent of that area is covered by sea ice. Some areas close to the Antarctic continent have sea ice all year long, but a much larger region of the Southern Ocean has sea ice for a smaller portion of the year, and in those regions the length of the sea ice season can vary significantly from one year to another.
The study used data from NASA’s Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) and the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imagers (SSMIs) and in the future will be extended with data from the National Space Development Agency of Japan’s Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) recently launched on board NASA’s Aqua satellite
This graphic shows trends in the length of the sea-ice season throughout the Southern Ocean over 21 years (1979-1999), as calculated from satellite data.