Thoughts from Judith Curry:
Yesterday, a reporter asked me how the IPCC came up with the 95% number. Here is the exchange that I had with him:
Reporter: I’m hoping you can answer a question about the upcoming IPCC report. When the report states that scientists are “95 percent certain” that human activities are largely to cause for global warming, what does that mean? How is 95 percent calculated? What is the basis for it? And if the certainty rate has risen from 90 n 2007 to 95 percent now, does that mean that the likelihood of something is greater? Or that scientists are just more certain? And is there a difference?
JC: The 95% is basically expert judgment, it is a negotiated figure among the authors. The increase from 90-95% means that they are more certain. How they can justify this is beyond me.
Reporter: You mean they sit around and say, “How certain are you?” ”Oh, I feel about 95 percent certain. Michael over there at Penn State feels a little more certain. And Judy at Georgia Tech feels a little less. So, yeah, overall I’d say we’re about 95 percent certain.” Please tell me it’s more rigorous than that.
JC: Well I wasn’t in the room, but last report they said 90%, and perhaps they felt it was appropriate or politic that they show progress and up it to 95%.
Reporter: So it really is as subjective as that?
JC: As far as I know, this is what goes on. All this has never been documented.
JC conclusion: Well, I have no idea what goes on in the sausage factory. 95% – take it with a grain of salt (or a stiff whiskey). That’s their story, and they’re sticking to it. Uncertain T. Monster is not happy.
I don’t know what this is, but sure as hell isn’t science.
[Update a while later]
A round up of initial reactions, for policy makers.
The general theme of obscurantism runs across the document. Whereas in previous years the temperature records have been shown unadulterated, now we have presentation of a single figure for each decade; surely an attempt to mislead rather than inform. And the pause is only addressed with handwaving arguments and vague allusions to ocean heat.
It was a blown opportunity to set the record straight.
[Update a few minutes later]
From comments: “SPM in a nutshell: Since we started in 1990 we were right about the Arctic, wrong about the Antarctic, wrong about the tropical troposphere, wrong about the surface, wrong about hurricanes, wrong about the Himalayas, wrong about sensitivity, clueless on clouds and useless on regional trends. And on that basis we’re 95% confident we’re right.”