Tom Nelson 
July 7, 2010
At the end of June, Southern Hemisphere mid-winter, the sea ice surrounding Antarctica was more than two standard deviations greater than normal. On June 30, Antarctic sea ice extent was15.88 million square kilometers (6.13 million square miles), compared to the 1979 to 2000 average of 14.64 million square kilometers (5.65 million square miles) for that day.
While recent studies have shown that wintertime Antarctic sea ice has a weak upward trend, and substantial variability both within a year and from year to year, the differences between Arctic and Antarctic sea ice trends are not unexpected. Climate models consistently project that the Arctic will warm more quickly than the Antarctic, largely due to the strong climate feedbacks in the Arctic. Warming is amplified by the loss of ice cover in the Arctic Ocean in areas that had been ice-covered for decades, and by the warming of Arctic lands as snow cover is lost earlier and returns later than in recent decades.
Moreover, rising levels of greenhouse gases and the loss of stratospheric ozone appear to be affecting wind patterns around Antarctica. Shifts in this circulation are referred to as the Antarctic Oscillation (AAO). As greenhouse gases have increased, and especially when ozone is lost in spring, there is a tendency for these winds to strengthen (a positive AAO index). The net effect is to push sea ice eastward, and northward, increasing the ice extent.