I don't know if you have already read and discussed conclusions presented in this article, but it suggests that GAC -2012 was not a major factor in record ice retreat. I thought it may be useful to the discussion on preconditioning of ice melt and summer ice cover.
"The impact of an intense summer cyclone on 2012 Arctic sea ice retreat". Zhang et al 2013.
That is a really good question, and I haven't blogged about why I think that the 2012 Great Arctic Cyclone (GAC 2012) played a major role in the 2012 melt.
What Zhang et al find, using the PIOMAS model is that "The simulated Arctic sea ice extent minimum in 2012 is reduced by the cyclone but only by 0.15 × 10^6 km2 (4.4%). Thus, without the storm, 2012 would still have produced a record minimum." So how can I possibly maintain that the 2012 Great Arctic Cyclone (GAC 2012) played a major role in the 2012 melt? This is especially when PIOMAS does such a good job, and I tend to view PIOMAS as the best available long term proxy for volume loss as a reanalysis product for sea ice. I have read Zhang et al 2013 several times, and I do get it. I have also read Parkinson & Comiso 2013, & Simmonds & Rudeva 2012.
GAC 2012 entered the Arctic Ocean around 3 August and eventually dissipated in the Canadian Arctic Archipelago on 14 August, its progress took it through the Arctic Ocean.
By 6 Aug 2012 it had neared its greatest intensity.
This state persisted until 8 August 2012.
By 10 Aug 2012 the cyclone was declining.
The period around 6 to 8 August is superimposed on the following graph of NSIDC Extent anomalies. Anomalies are the difference from an average seasonal cycle, here the average is for 1981 to 2010.
So that is basically it. Before the cyclone hit extent anomalies were roughly level, indicating losses around the average. This state followed an earlier June loss of extent. In general that pattern is similar to other recent summers, such as 2010, 2011, 2013 and 2014. However once the GAC 2012 hit a new regime of loss at substantially greater rates than the average started, and it started exactly when GAC 2012 hit.
When I look at the above graph, to me it begs the question of Zhang et al 2013: Did GAC 2012 really just cause 0.15M km^2 of loss? It's not a rigorously scientific position, evidence from a reliable model counters it, but when I look at what happened in terms of anomalies of sea ice extent, it is too much for me to swallow that the Great Arctic Cyclone of 2012 had little impact.