This plot shows the Antarctic sea ice extent, the Arctic sea ice extent, and the total sea ice extent plotted against time.
Like in previous post I chose 2012 only because it is the most recent complete year in this data set.
Take a look at the minimum, the maximum and the range of the sea ice extent.
||Minimum Antarctic sea ice extent
||3.11 x 106 km2
||Maximum Antarctic sea ice extent
||19.48 x 106 km2
||Range of the Antarctic sea ice extent
||16.37 x 106 km2
||Minimum Arctic sea ice extent
||3.37 x 106 km2
||Maximum Arctic sea ice extent
||15.25 x 106 km2
||Range of the Arctic sea ice extent
||11.88 x 106 km2
The range of Antarctic sea ice extent is 16.37 x 106 km2, and the range of the Arctic sea ice extent is 11.88 x 106 km2.
The Antarctic and the Arctic do not "balance" in sea ice extent - the Antarctic variations are much larger.
Look at the shape of the annual cycle. I said previously that in the Antarctic the seasonal cycle of sea ice extent is not symmetrical. Sea ice grows slowly and steadily before decaying relatively rapidly: the melt period is shorter than the growth period.
In the Arctic the time sea ice grows is roughly similar to the time sea ice melts.
So they do not "balance". The seasonal cycles, ranges, minimums and maximums are different,
The annual cycle of the Arctic and Antarctic sea ice extent is very different.
We know that the extent and thickness of the Arctic sea ice is decreasing. See for example what Tamino wrote in Feb 2014.
But what about the Antarctic? The extent of the sea ice has broken records for the satellite era. (This is a very funny article making some claims about what that means - if you want a clue what is the difference between glacial ice and frozen sea water?).
Some believe the observed reduction in the Arctic sea ice volume is balanced by the increase in the Antarctic sea ice extent. So we should look at the black line in the plot above.
I will get onto why I don't think that is a good idea in a coming post.
Here is the plot animated with 1 second = 10 days
About the data
The data set is from the National Snow and Ice Data Center Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data.