I'll also mention a few other predictions, or methods:
Climatology 15a is the average of the first 15 years. 15b is the average for the last 15 years (not counting 2009!). Climatology 30 is the average of the first 30 years of the satellite record.
Persistence is to say that this year's ice will be the same as last year's. For atmospheric temperatures, persistence is a pretty good forecaster for the first two days (at least in the sense that it is closer to what you see than climatology). For sea ice, it is not so good, beating climatology only 17 of 30 years. It's interesting, however, that its losses are strongly clumped. In the 14 years from 1990-2003, persistence won 2 and lost 12 versus climatology-30. In the remaining 16 years, it went 15-1.
Update: Per William's request, I'll add the ARCUS estimates (as given in the full report) for June's report. I believe the values all were rounded to the nearest 0.1 million km^2, so for consistency will list mine at 4.9 here.
|Canadian Ice Service||5.0||0.36|
|Hori, Naoki, Imaoka||5.0||0.36|
|Nguyen, Kwok, Menemenlis||4.9||0.46|
|Lindsay, Zhang, Stern, Rigor||4.9||0.46|
|Kaleschke and Halfmann||4.9||0.46|
|Fowler, Drobot, Maslanik||4.9||0.46|
|Arbetter, Helfrich, Clemente-Colon||4.7||0.66|
|Stroeve, Meier, Serreze, Scambos||4.6||0.76|
|Kauker, Gerdes, Karcher, Kaminski, Giering, Vossbeck||4.3, 4.6||1.06, 0.76|
To judge from the graphic that accompanied, however, the bar chart was done with figures that had more precision, as Kaleschke and Halfmann's 4.9 is clearly higher than Fowler and company's.