If the arctic climate were in perfect balance then all of the melt in any given year would be replaced by an equal amount of freeze. We would have a seasonal cycle that wouldn't necessarily be a sine wave, but it would be repeated year after year with equal amplitude minimums and maximums.
The fact that there is overall loss does NOT mean the process is driven by more melt - only that melt exceeds freeze. As I tried to explain, there are 3 possibilities mathematically (assuming the process is thermodynamic and the loss is not due to chaotic variability and the time window open to us just happens to be when the random chaotic features lead to a loss).
If we accept that the loss is a trend, and we know there are only 3 possible explanations, examination of the data tells us which of these possibilities is actually in effect - both melt and freeze are increasing, but melt is on average larger than freeze. But even knowing this does not tell us whether the losses are due to winter or summer processes.
We know that global warming does not just manifest itself in a particular month or season, but that does not mean that it's uniform. Chris is actually asking (I think), Is the Arctic thermal balance more anomalous in winter or summer? Arctic sea ice extent, area and volume anomalies are just indicators of this energy imbalance.
The intuitive answer is that the losses are driven by summer melt processes. The data seems to bear intuition out: The correlations between the preceding winter and summer melt are very low. The correlations between melt and the following freeze are significant (though barely at 95% and with a small sample size).
BUT .... arctic winter warming is 4 times larger than summer warming! Hmmm .... back to the drawing board.
A consistent story has to mesh with all the facts. The fact that winter warming is greater than summer warming in the Arctic is not, on its face, consistent with an explanation that says summer processes are responsible for the ice losses.
In looking for a freeze-melt correlation - and finding none - I believed the preceding winter's volume gain told us little about the summer melt losses. This may be misleading. Just because it's true doesn't actually prove anything. What if volume gain isn't a particularly significant attribute of winter?
In fact, after a couple days reflection I believe that is actually the case - that volume gain per PIOMAS tells us very little about winter. Arctic temperatures historically on average fall to -45 C°. That's far lower than necessary to create ice. There is also a thermodynamic limit to how thick sea ice can grow over the winter. So a 5 C° warming during winter may not lead to any less ice, but it will lead to more summer losses - since less energy is needed to raise the ice temperature to the melting point.
Take a look at the
Interpolated surface OLR for February 2013 and compare it to previous Februarys. One has to go back to at least 2004 to find anything similar. Probably 2002 or earlier. It's also pretty easy to show that the February OLR plots are very closely related to the summer losses. Rank them in order just by visual appearance and you'll come out very close to the same order as the actual losses.
In summary, the fact that PIOMAS volume gains for the preceding winter do not correlate to summer losses is probably misleading. We used this lack of correlation to prove to ourselves that winter didn't determine summer losses - but the lack of correlation only tells us that volume gain is not correlated to summer losses, not winter in general.
The winter OLR plots, particularly January and February, tell a different story. The OLR plots should be a rough proxy for ice temperature. And there's a huge energy difference between melting ice that might be at -40 C° as opposed to ice that might be 'only' -30 C°.
Of course I reserve the right to change my mind - again
