Have to bite the bullet here and discuss my guesses for the September 2014 Arctic sea ice extent average. The thing which has made them so difficult is that they're so different from each other. Now, one method I've retired. It was simply so bad last year that there's no point in continuing it. That is the one I did based on a population growth (of ice-free area) curve.
That leaves, however, two different model-based guessers. The first one, which appears at the Sea ice prediction network as 'Wang', is based on doing a statistical regression between what the CFSv2 (climate forecast system, version 2) predicts for September ice area and what is observed. The second also uses CFSv2, but in a different way. Namely, we know that the model is biased towards ice being too extensive (which the Wang method addresses statistically) and to being too thick. The Wu method is based on thinning the ice and seeing what the extent is thicker than a critical limit (60 cm it turns out). (Both Wang and Wu work with me, or vice versa, and we discuss how to work on these guesses.)
The guesses are:
June -- Wang -- 6.3 million km^2 0.47 stdev
July -- Wang -- 5.9 million km^2 0.47 stdev
July -- Wu -- 5.1 million km^2 0.56 stdev
June -- Wu -- 4.8 million km^2 0.65 stdev
One of the things to notice is that the two estimates moved towards each other from June to July. Wu rose, the higher Wang declined. The second is, the Wu method has a standard deviation (variability of its estimate) that is double what it was last year. Whatever is going on in the model, it is much less self-consistent in previous years. Much more uncertain. This is one of the reasons for ensemble modeling (part of the Wu approach).
You can also see that the Wang estimate is the highest of all -- even higher than the Watts up with that group estimate. This is true in both June and July.
So, what's up? Well, I'm not sure. Some of it is certainly related to sea ice thickness estimates. Xingren (Wu) did a different approach based on thickness for June, which we didn't submit, but which landed in between the official June estimates from Wang and Wu. With the step towards convergence from June to July between Wu and Wang methods, I'm inclined to guess (a meta-guess) 5.5 million km^2 for September. If this were to occur in reality, it probably suggests something important. What, exactly, I'm still pondering.