Dave Roberts is the resident upholder of the CAGW consensus at Grist. Here he is lecturing on climate change at TED, and boy is he worried about the future - "Hell on Earth" is one of his more optimistic predictions.
I was struck by Roberts' comments about climate sensitivity. It seems to me that he gets completely confused over the difference between climate sensitivity and climate impacts. Having discussed the ad-hoc nature of the 2 degree target that is often cited as the threshold above which climate change becomes dangerous he says this:
The bad news on this 2C number is twofold. First of all, all the latest science done in the last ten to fifteen years has pointed to the conclusion that those impacts we thought were going to happen around two degrees centrigrade are in fact going to happen much earlier. The climate more sensitive to this added greenhouse gases than we thought. So if those were the impacts we were worried about then the real threshold of safety ought to be something like 1.5 degrees centrigrade...it's a growing scientific consensus that 2 degrees centigrade is dangerously high.
If the climate is more sensitive to carbon dioxide then it warms more quickly for a given change in greenhouse gases. I don't think it changes the temperature at which any given impacts occur.