For reasons that need not concern you, I found myself the other day reflecting upon the claimed 97% climate change consensus. Ninety-seven has always struck me as a strange yet ubiquitous figure that seems to crop up in surveys with a frequency that hints at non-randomness. Why does it never seem to be ninety-six or ninety-eight percent? The answer I have given myself is that these two even numbers are not spiky and idiosyncratic enough to carry the required message of scientific credibility. Furthermore, ninety-six is just a tad too low to impress, and ninety-eight is just a tad too high to be believed. Only ninety-seven hits that sweet spot that Goldilocks cannot resist.

To confirm my suspicions that ninety-seven occupies a favoured position in the survey results popularity charts, I decided to google it, just to see the variety of claims that fall into the same fake credibility niche occupied by the climate consensus. I grant you that a mental space in which such an exercise might seem a good idea is a strange one to occupy, but we deniers are queer folk, as Lewandowsky et al have been keen to point out. Unfortunately, my research proved futile since, rather than finding a myriad of claims based upon the mythic ninety-seven percent, I found just the one, repeated endlessly:

“97% of women say they have been victims of sexual assault.”

Yes, it seems that the ninety-seven percent meme has now been co-opted to further the idea that women are no longer safe in society. If the number ninety-seven finds employment in the service of any other agenda, then I’m afraid the evidence of it must be buried on page ninety-seven of my google search results (not ninety-six or ninety-eight, mind you). Fortunately, however, this single example currently choking the meme pool does at least perfectly illustrate the underlying problem with all such claims:

It simply makes no sense to make a precise claim regarding a vague notion.

In the case of the sexual assault statistic, the vagueness stems from the lack of a reliable definition of what constitutes sexual assault – at least in the minds of those answering the surveys. At one extreme we are dealing with crimes of the most heinous nature, but at the other extreme there are events that may simply be the unwanted attentions that are inevitable given the nature of the mating game. When does an approach become an assault? It can’t surely be left at the whim of the victim to declare. But if it is, we have a problem because the concept will have become hopelessly subjective.

In fact, the concept of ‘assault’ is a classic example of the sort of vague noun beloved of linguists and philosophers of vagueness. There has to be borderline cases that suffer from arbitrariness and the sorites paradox (e.g. if an unsolicited smile is not an assault, then a smile that is barely distinguishable from a leer must be equally innocent, and so on). As a consequence of this vagueness, any claim to a precise quantification has to be bogus. Similar examples can be found in medical science where statistics relating to vague notions, such as obesity, are quoted with far too much confidence and precision.

The same problem, of course, exists with the precise claims relating to climate change consensus. When quantifying the consensus, the vague definition of the belief under investigation gives enough latitude for the researchers to gravitate towards any precise quantification that floats their boat – but it still makes no sense to claim a precise value when the position of belief under study is so loosely defined. The ninety-seven figure may have been chosen for its credibility, but the truth is that its precision is the very thing that signposts its untrustworthiness. Even more damning is its apparent constancy in the face of scientific progress. The consensus should be increasing, but the declared value is not; the enchantment of the number ninety-seven is just too strong. It is not a constant of nature, but when there is an idea to be nurtured, it becomes a constant of nurture.

Another classic example of a constant of nurture within the field of climate science is the stated range of plausible values for the Equilibrium Climate Sensitivity (ECS). This was first guessed at back in the sloppy seventies and that guess has retained a constant presence ever since. As knowledge is gathered one can either use it to make an estimate more precise or one can use it to increase confidence in the currently stated level of precision. Strangely, over forty years, it is only the latter that seems to have happened with regard to the ECS value – we started out thinking we don’t know the value precisely, but now we know for certain that we don’t know it precisely. We seem to have done little more with our newfound insights than to bolster our confidence in that regard. This strange phenomenon only starts to make sense when one stops thinking of ECS as a constant of nature and starts thinking of ECS as a constant of nurture. Back in 1997, Jeroen P. Van der Sluijs, Professor, Theory of Science & Ethics of the Natural Sciences, Bergen University, explained this constancy by stating:

“[T]he stability can also be seen as a function of an implicit social contract amongst the various scientists and policy specialists involved, which allows ’the same’ concept to accommodate tacitly different local meanings…The maintained consensus about the quantitative estimate concerning a central scientific concept in the anthropogenic climate change field, namely climate sensitivity, operates as an anchoring device in science for policy.”

So the main advantage of holding the ECS uncertainty range constant down the years is that it provides a firmly constant framework within which to perceive the level of risk posed by climate change, particularly if that view is informed by the concept of ‘actionable uncertainty’, as proposed by Lewandowsky (That’s the second time I have mentioned his name; as with Beetlejuice, I will have to be very careful not to mention it a third time).

As such, the accepted range of values for ECS is a ‘constant’ that guides the science just as readily as Newton’s constant of gravity (G). The only difference is that G is a constant of nature and the ECS range is a constant of nurture. A narrower range for the latter would be more valuable to the science but less valuable to the politics, for which too many social contracts have already been signed.

For different reasons, there is an arbitrariness to both the ninety-seven percent consensus figure and the ECS range. In both cases, we are invited to think that the values are purely the outcome of an unbiased analysis of the available data. In practice, however, there is no such thing as unbiased analysis, and the degree to which bias may have been applied can be seen as a reflection of the degree to which a result serves to nurture favoured ideas. It is under those circumstances that a constant of nature can morph into a constant of nurture.

I’ll leave the last word to Stephan Lewandowsky.

Oh my God! What have I just done?