The argument about excessive certainty from partisans has come up frequently, and has recurred at Curry’s. I think the argument is without merit. I have never seen excessive confidence from the scientific sector about climate. Everybody admits that there is much we don’t know. The possibility of “unpleasant surprises in the greenhouse” has long been acknowledged.
Let me summarize once again the “uncertainty is not your friend” argument.
Despite popular perception, there is no debate in physical climatology about first order processes.
You don’t find Lindzen or Christie or Spencer or even Michaels questioning the accumulation of CO2 or the existence of a CO2 forcing. You have to sink even lower than Singer to find someone saying something like that.
What is going on in physical climatology that bears any resemblance at all to the public vision of it is arguments over an estimate of a quantity that must exist (the sensitivity) and its confidence bounds. (Typically, the sensitivity is expressed as degrees C equilibrium warming per doubling of CO2.)
A soi-disant “skeptic” climate change naysayer can be relied upon to implicitly or explicitly make the following case about the physics:
- the mainstream greatly overestimates the sensitivity
- uncertainty is large
- policy should therefore act as if the sensitivity is small and the uncertainty is small
It’s my belief that the case from their 2 to their 3 is so incoherent that the argument can be defeated there without much reference to science.
(Recall Judith Curry’s claim that the temperature sensitivity to CO2 doubling is between zero and ten C.It seems to me that Dr. Curry does not act coherently with a belief that 10 C is a plausible sensitivity! This puts us at enormous risk. Suppose the middle were excluded, and we had merely a 50/50 chance of a sensitivity of 0 and a sensitivity of 10 C. Wouldn’t the 10 C outcome dominate our rational behavior? Nevertheless it’s fair to say that Curry’s fan base embraces her fascination with uncertainty and somehow associates it with a no-policy stance.)
It is possible to argue endlessly over point 1. However, the so-called skeptics habitually make the policy case themselves by advocating point 2. Insofar as stopping the futile nitpicking over science in the public sphere and moving on to reasonable policy is concerned, they have already given us the argument we need.
The position to take in the policy sphere is that either the mainstream is right OR the uncertainty is large. A modest understanding of risk weighting can carry the day from there.
Quoting myself from 1999:
- It is clear enough that a change of 20 C would be cataclysmic, whether that change is a warming or a cooling. It is also clear enough that a change of 0.2 C is of little consequence, and may be on net beneficial. There is no reason to believe that this function is linear. The contemplated changes (~2 C) are large enough that we can not have total confidence that the impacts will not be catastrophic.
- There is no plausible argument that any particular climate change will have a beneficial impact comparable to the worst plausible case negative impact.
- The risk-weighted cost of unrestrained anthropogenic perturbation must therefore be dominated by the fact that the plausible worst cases have more cost than the plausible best cases have benefit.
If we think about the situation fairly, Curry does us (those of us who want a sane policy) a great favor by playing up uncertainty.
It is not necessary to defend the science to get to a sane policy. It is enough to say “if you argue that the science is weak, you must admit that the uncertainty is large” and that “there must be some number that represents the sensitivity”. Then proceed directly to risk arguments.
Yet so many people get this backwards. In order to defend status quo/laisser faire emissions policy, you must advocate for very low uncertainty. You must be absolutely confident in a scientific position that is not in fact in line with most experts. Otherwise the risk remains high.
I’ll have more to say about Steven Mosher’s recent article at Curry’s, and I suspect some of the more postnormally-oriented may have their own responses, but I wanted to thank Mosher for acknowledging that I made the “uncertainty is not your friend” argument long ago. Being the slacker that I am, I am not especially attached to getting credit for things, but this may have been my most important single contribution. I appreciate Eli’s efforts in working to establish this, and Mosher’s recognition of it.
Here I just wanted to repeat the main thrust of it, and reassert my claim that it is not mainstream science that has been making claims of excessive certainty, implicitly or explicitly. All we are claiming is that it is very hard (and getting harder) to exclude a very large risk. If there is excessive confidence, it is coming from the critics.
There is nothing magical about climate. Like anywhere else, more uncertainty means more risk.
Image: Judith Curry at the keyboard via UCAR