This blog is written by Canadian journalist Donna Laframboise. Posts appear Monday & Wednesday.
Scores of scientific minds. So much tomfoolery.
I’ve observed that the Intergovernmental Panel on Climate Change (IPCC) is meddling with the glossary definition of six terms central to the climate discussion – such as the definition of ‘global warming’ itself – at this eleventh hour.
Other changes are also underway. The IPCC has a formula for expressing levels of confidence in its own conclusions (see its explanation here). The Executive Summary that appears at the start of this report’s Chapter 1, for example, tells us the IPCC has ‘high confidence’ in 11 of its declarations and ‘medium confidence’ in four others.
Those judgments are also being massaged.
The scientists who wrote this report said they had ‘high confidence’ that the greenhouse gases humanity has already emitted won’t cause more than 1.5ºC of warming. Following the multi-day meeting with the political folks, that’s being downgraded to ‘medium confidence’ (Chapter 1, page 4, line 30).
Similarly, scientists’ ‘high confidence’ that the Arctic won’t experience ice-free Septembers at 1.5ºC of warming is being changed to ‘medium confidence’ (Chapter 3, pages 140-41).
Scientists had ‘medium confidence’ that some species will be at more risk of local (aka non-global) extinctions should warming reach 2ºC. That’s now being changed to ‘high confidence’ (Chapter 3, page 8, line 45).
Scientists’ ‘high confidence’ that “any increase in global temperature” will “affect human health” is being altered to say the IPCC has ‘high confidence’ increased warming will “affect human health, with primarily negative consequences” (Chapter 3, page 11, line 6).
And on and on. With few exceptions, the changes point in one direction – toward pessimism. When IPCC scientists sound too optimistic about the future, the political people apply a thumb to the scale.
Big picture, though, this all amounts to intellectual masturbation. That scores of scientific minds participate in this pointless exercise makes one despair.
The IPCC report writing process is wholly subjective. As climatologist Judith Curry explained five years ago, when IPCC personnel declare they are 95% vs 90% confident about something, there’s no math behind those numbers.
Here’s part of an exchange she had back then with a journalist:
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 [the] 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.
Out here in the real world, criminologists have known for more than 30 years that “confidence is not a reliable predictor of accuracy.” Eyewitnesses who are certain that events occurred in a particular manner can be profoundly mistaken (see here, here, and here).
By tracking predictions over the long term, psychologist Philip Tetlock has discovered that personality types who are confident they know how the future will unfold are less likely to make accurate forecasts than personality types who make more hesitant, highly contingent ones (see here, here, and here).
The fact that IPCC scientists have ‘high confidence’ versus ‘medium confidence’ in any particular conclusion is meaningless. No sane person should take such judgments seriously until the IPCC explains why the above concerns don’t apply to its own personnel.
To sum up, therefore:
1. IPCC reports are a collection of subjective judgment calls.
2. Political operatives at the IPCC can – and do – override confidence levels determined by scientists.
3. These confidence levels likely have no connection to reality.
|Superforecasting: The Art and Science of Prediction
Philip Tetlock & Dan Gardner
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