Arctic and Antarctic sea ice are very different because of the geography of the two poles. In the Arctic we have an ocean surrounded by landmasses, while in the Antarctic there is a continent (Antarctica) surrounded by the Southern Ocean. This means that sea ice (frozen sea water) around Antarctica can easily drift north into warmer waters during the Antarctic summer and melt. Arctic sea ice can’t drift south so easily, being blocked by landmasses. This leads to a major difference in the behavior of Arctic and Antarctic sea ice – historically, about 50% of the Arctic winter sea ice survived the summer melt period, while only about 17% of Antarctic winter sea ice survived the summer. They are very different places.

To answer your question, the Antarctic summer sea ice cover has not been rapidly decreasing like the Arctic sea ice. Also, the Antarctic continent has not been warming dramatically like the Arctic has (large areas of Antarctica have been getting cooler, actually). This has to do with differences in the way the atmosphere circulates around the two poles (again because of geographical differences). This is a great example of how changes in climate are regional, not global. Even though climates of different regions are all connected, they do not all shift in the same direction when given a shove.