10%: the United States has a historically hot summer.
This is only notable because it's the only factor that could get cap-and-trade legislation through a Republican House. (Whose bright idea was it to have the 2009 Copenhagen climate change summit in winter? The juxtaposed headlines with the winter storm may have set back the legislation indefinitely.)
(Even though it wasn't the warmest on record, the fact that it came in second is evidence that I probably should have estimated this at somewhere around the Intrade global temperature figure of 34%.)
http://predictionbook.com/predictions/2098 ; what data source do you plan to use?
6Unnamed
Intrade gives 2011 a 34% chance to be the warmest year on record, so 10% seems low.
But that's global annual temperature, not US summer temperature. The closest thing I could find to US summer temperature with a 5 minute search is the NASA GISS dataset for the average northern hemisphere land-surface temperature in June-August. The record summer high for the northern hemisphere was broken in 2010, 2005, 1998, 1995, 1990, 1988, 1987, and 1983, which also suggests that the probability of a record-breaking US summer is around 30% rather than 10%.
As we did last year, use this thread to make predictions for the next year and next decade, with probabilities attached when practical.
Happy New Year, Less Wrong!