The retention of more sea ice in September 2013 has increased the overall thickness and volume of the ice pack compared to recent years. Antarctic sea ice remains significantly more extensive than average.
Over the past few years, winter winds have been transporting less ice out of the Arctic than has been forming, so the average age, thickness and volume of ice is increasing. If the recent wind patterns continue, then the amount of ice will continue to increase. It has nothing to do with CO2.