In the wake of the Press Gazette "debate", I was watching an exchange of views on Twitter between BH reader Foxgoose and Andrea Sella, a University College London chemist who moves in scientific establishment and official skeptic circles.
Sella was explaining how persuasive he found the observational record of climate:
Think like a scientist! Temperature is only a proxy. Energy balance is real issue & C19 physics is alive and well.
Like Warren Buffett you mustn’t be affected by shorter term fluctuations.
As I said, don’t just look at surface temps. Look at sea level and global ice mass too. All part of same.
I gently inquired of Sella whether he there had been any statistically significant changes in these records, to which he responded:
1.56 ± 0.25 mm over a century isn’t significant?
I then pointed him Doug Keenan's one-page article about why you can't decide about significance just by looking at a graph.
This brought about the following rebuke from Richard Betts.
Your 'statistical significance' argument is silly: http://wmbriggs.com/blog/?p=8061
The link is to a Matt Briggs article on why statistical significance is a flawed concept. As readers here know, Briggs is a Bayesian and sees flaws in the frequentist approaches to statistics. This is fine, but frequentists will of course shoot back that there are problems that are as bad or worse with the Bayesian approach. I'm not enough of a statistician to come down on one side or other of this particular fence and I can cope with people making arguments under either paradigm.
But people do need to be consistent, a point Briggs makes in the article Richard B linked to.
If we seek to understand this physics, it’s not likely that statistics will play much of role. Thus, climate modelers have the right instinct by thinking thermodynamically. But this goes both directions. If we have a working physical model (by “working” I mean “that which makes skillful predictions”) there is no reason in the world to point to “statistical significance” to claim temperatures in this period are greater than temperatures in that period.
Why abandon the physical model and switch to statistics to claim significance when we know that any fool can find a model which is “significant”, even models which “prove” temperatures have declined? This is nonsensical as it is suspicious. Skeptics see this shift of proof and rightly speculate that the physics aren’t as solid as claimed.
This brings me neatly back to where we started. Andrea Sella points to the observational records and implies that I should draw conclusions from them. My response is that if you think we can learn something from them, show me how the change is significant. If you think statistical significance is a flawed concept and that we should be examining the congruence of observations with the output of physical models then do not wave temperature graphs in front of my nose. Tell the public loudly and clearly that we can learn nothing from observational records on their own and that we need a physical model. Then tell us why your physical model is sound despite estimating a value for aerosol forcing that is at material variance with observations, and despite it producing estimates of warming that vastly exceed observations.
And you absolutely must not, as the Met Office has done, tell the GCSA that warming is "significant" without any statistical foundation. Do not, as the Met Office has done, tell Parliament that warming has been "significant" without any statistical foundation either. Doing things like this will leave you having to beat an embarrassing retreat to a position of "we don't use statistical models", directly contradicting your earlier pronouncements. It will also leave you in the tricky position of having to explain whether you think the IPCC is "silly" for using statistical significance, or indeed whether your own employer is "silly" too.