- 7.03 million km^2 -- Climatology 1979-2000
- 6.67 million km^2 -- Climatology 1979-2008
- at least 5.5 million km^2 -- Joe Bastardi at WUWT
- 5.31 million km^2 -- Linear Trend Climatology 1979-2008
- 5.0 million km^2 -- Wang, Wu, Grumbine model, June
- 4.8 million km^2 -- Wu, Grumbine, Wang model, June
- 4.61 million km^2 -- NSIDC observed September Average sea ice extent
- 4.6 million km^2 -- Wu, Grumbine, Wang model, August
- 4.4 million km^2 -- Grumbine, Wu, Wang statistical ensemble, June
- 4.4 million km^2 -- Crandles, L. Hamilton (at Neven's, but also cited in comments here)
- 3.9 million km^2 -- Alastair (in comment here)
It's a good sign that we were within that range. Also, 0.5 million km^2 is the variability estimated by almost all groups that provide an estimate for it. Even though that number is suspiciously round, we actually arrived at it by data analysis. It's a statement of how much the ice pack varies, rather than the quality of the methods. The quality of the methods is how their error compares to the 0.5.
For the coming year, we've got some modifications in mind (experiments) for the Wu et al. approach, and I've already made some for the statistical ensemble.
Plus, I'm going to be taking a look, perhaps getting Wu to play too, at whether this past winter's heavy sea ice cover in the Bering Sea was something we could have (or did) estimate in advance. The model runs are already done. It's 'just' a matter of analyzing them.