We had a talk at work today by a chap (eminent mathematician I think) about looking at the distribution of extremes in the temperature record and trying to say something about detection. The problem is that extremes are statistically rather unstable and all he could say was that he didn’t detect GW; he didn’t appear to understand that all that means is that his method isn’t very powerful…
[Update: JF points to http://www.arxiv.org/abs/physics/0509088 which is the paper]
And when I say global, actually he was looking at Philadelphia, daily data, last 125 years. He pretty well went out of his way to demonstrate his lack of met knowledge (didn’t know IPCC; didn’t know *where* the met station was in Philly; hadn’t managed to find many other longer records in the course of browsing the web; etc). Very much a mathematician picking up some met data and playing with it. Which is fair enough *unless* you start taking his conclusions seriously.
Anyway, what he was doing (via some maths) was noting that if you have a stationary record, then record-breaking highs (or lows) get less and less frequent as time goes on. Whereas if you have a trend, then the frequency tends to a constant. Unfortunately… when testing his method, the “trend” he tried fitting was 0.6 oC/C, which isn’t a very good approx to the temperature record. Whether this matters is unclear. More significantly, his results were simply inconclusive: he failed to detect a trend, but he also failed to rule out a trend.
It was pointed out to him (by me and others) that if you really want to detect a trend… err… why not just look at the trend? All the record-fitting its fun maths, but (as a detection method) really very weak. It wasn’t quite clear whether this had never occurred to him, or if he knew it perfectly well but wasn’t going to mention it first on the off chance that no-one else would think of it. There seemed to be some suggestion that he was confusing (not in his maths, but perhaps in his motivation) the difference between GW-will-lead-to-more-extremes and extremes-are-useful-for-monitoring-GW.
[Incidentally, this is my first-ever scheduled post. Hope it works. I wrote far too many yesterday. Like the London buses]