September is when the melt of the Arctic Sea Ice stops, and the re-freeze starts. We are probably not at the minimum yet, but the amount of melting is starting to level off so we can see where we are. The above graphic, made here (go and play with the interactive graph) shows the first ten years of ice freezing and remelting in the data set to use as a baseline for comparison, and the present year. Yes, there is much less sea ice on the northern end of the planet than usual.
This version of the graph shows the years with less ice, so far, than the present year. This includes the famous 2012 when the ice melted a lot lot more than usual, instead of merely a lot more. 2007 probably had less ice than this year will see, but we can’t be sure yet. 2011 and the present year are almost the same. Again, we’ll see but currently 2011 had a tiny bit less sea ice extent.
So, 2015 will end up being the second or third most ice free year on record. Keep in mind this is only surface, not volume. Still, surface is very important because it is part of a feedback system; the more surface ice the more reflection of sun’s energy back into space, the less surface covered with ice, the more the Arctic sea is warmed by the sun during the summer.