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	Antarctic Sea Ice Increases over Past Two Decades By SPACE.com Staff posted: 03:20 pm ET 22 August 2002

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In a surprising departure from other findings that point to a warming planet, a NASA researcher has found that the amount of ice in the Antarctic increased from 1979 to 1999, as measured by satellites.

Many recent findings have detailed the decline of the ice cap in the Arctic, at the top of the world. These new results from the Southern Hemisphere imply that global climate change involves regional variations.

Changes in ice cover are important not only because they indicate temperature changes that have occurred; the changes can effect future temperatures. With more ice, more solar radiation is reflected away from Earth. The ice also insulates oceans from the atmosphere. Less ice has the opposite effects.

In the new study, published in the Annals of Glaciology, Claire Parkinson of NASAs Goddard Space Flight Center analyzed the length of the sea ice season throughout the Southern Ocean to obtain trends in sea ice coverage. On average, the area where 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.

"You can see with this dataset that what is happening in the Antarctic is not what would be expected from a straightforward global warming scenario, but a much more complicated set of events," Parkinson said.

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.
Credit: Claire Parkinson, NASA GSFC

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.

Parkinson also looked at how various regions of the Antarctic compared to one another.

Regionally, the Ross Sea, on average, had its sea ice seasons getting longer, while most of the Amundsen Sea and almost the entire Bellingshausen Sea had their sea ice seasons getting shorter.

"The Antarctic sea ice changes match up well with regional temperature changes," Parkinson said.

The study used data from NASAs Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) and the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imagers (SSMIs).