In contradiction to some recent studies, he finds that the airborne fraction of carbon dioxide has not increased either during the past 150 years or during the most recent five decades.
A statement like that requires some serious historical research, and a consideration of measurement accuracy. So I don't expect James Hansen to say, "Oh, gosh, maybe my elaborately tailored snafu of a computer model is in error." (I've made an assumption about his computer model: that it would be just as bad, or a little less so, than the program disclosed in the Freedom of Information files from the Climate Research Unit in Britain. Not a bad assumption when I find his supervisor saying the model is wonky.
The thing about bad programming is that people who play with it a lot LIKE all those fuzzy edges. Instead, I expect assertions that, "So it's been stable for the past 160 years, and shows no change when you consider the last 50 years. It could change, you know! Catastrophically! Pay me lots more money and I'll study it!"