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Warming, Poles Apart: Earth Image of the Week October 26, 2012
Antarctic ice graphic
Sea ice around Antarctica grew to the greatest size ever before observed on September 26, 2012.
Just two weeks after the Arctic Ocean’s sea ice melted to its lowest coverage ever observed, the ice surrounding Antarctic expanded to a record size.

Sea ice around the South Pole covered 7.71 million square miles on September 26, 2012, the date of this year's annual wintertime maximum.

The image to the right shows sea ice coverage on that date based on data from the Special Sensor Microwave/Imagers orbiting in the U.S. Defense Meteorological Satellite Program.

Previous satellite observations since 1979 indicate that while Antarctic sea ice varies greatly from year to year, it has grown almost 1 percent per decade on average despite the contrasting record melt at the other end of the world.

While the expanding ice in the Southern Hemisphere seems to contradict a warming planet, it and the Arctic melt are both the result of humankind’s altering of the chemical composition of the atmosphere.

The Antarctic sea ice maximum nearly coincided with the ozone hole’s greatest expanse of the year on September 22.

The use of chlorofluorocarbons as refrigerants, and for other applications in the 20th century, caused the stratospheric layer of ozone to significantly thin, creating the ozone hole.

Those chemicals are currently being fazed out through a landmark international agreement, but scientists say it is likely to take decades for the ozone hole to heal significantly.

Stratospheric ozone acts as a greenhouse gas, capping in the planet’s warmth. So the loss of the ozone layer above Antarctica in the southern winter has allowed the region’s heat to radiate into space through the ozone hole.

This has resulted in Antarctica bucking the trend of warming seen elsewhere around the world. Another factor in the expanding ice is global warming’s effect on the southern jet stream.

As the middle latitudes have warmed, it has caused that high-altitude river of air to strengthen and move closer to the pole. This also has brought stronger surface winds, which have spread the winter ice over a larger area.

At any rate, the increase in Antarctic sea ice is very small compared to the dramatic melt the Arctic Ocean has undergone over the past decade.

Full story and image: NASA