Climate sensitivity to CO2 is typically defined as the amount of warming that would be caused by CO2 levels rising from pre-industrial 280ppm to a doubled concentration at 460ppm. Via Ron Bailey, here is what Hadley presented at Bali today:
Hadley climate models project that if atmospheric concentrations of GHG were stabilized at 430 ppm, we run a 63 percent chance that the earth’s eventual average temperature would exceed 2 degrees Celsius greater than pre-industrial temperatures and 10 percent chance they would rise higher than 3 degrees Celsius. At 450 ppm, the chances rise to 77 percent and 18 percent respectively. And if concentrations climb to 550 ppm, the chances that average temperatures would exceed 2 degrees Celsius are 99 percent and are 69 percent for surpassing 3 degrees Celsius.
I encourage you to check out this post wherein I struggle, based on empirical data, to get a sensitivity higher than 1.2, and even that is only achieved by assuming that all 20th century warming is from CO2, which is unlikely. A video of the same analysis is below:
However, maybe this is good news, since many climate variables in 2007, including hurricane numbers and global temperatures, came out in the bottom 1 percentile of predicted outcomes from climate models.