2011-06-11 20:22:39Phil Jones significant temp rise - ask for help & stats question!
Robin Webster

Hi all

This is Robin from Carbon Brief in the UK, with a request for help! Some of you may have seen that the BBC reported an interview with Phil Jones in which he said that acc. to CRU figures, temperature rise since 1995 is now significant to the 95% level. We've written it up at Carbon Brief - see here http://www.carbonbrief.org/blog/2011/06/global-warming-since-1995-statistically-significant. 

The reason I'm asking for help is two-fold - first as a young website, we are still building up our community of commentators, and over the last 15 hours or so that thread has been bombarded with skeptics (many of whom I suspect have nowhere else to go to write about this as the BBC post is closed to comments). We could do with some more scientific literacy to redress the balance. So if any of you fancied heading over there for a bit, I would be very grateful.

Secondly, a specific question on stats. A guy called Doug Keenan has 'rebutted' the Jones statement, saying that the trend is NOT signifiicant using the methodology in the 2007 IPCC report (http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch3sappendix-3-a.html). He says:

"Following is an R session showing the statistical calculations. The temperature data (HadCRUT3) was downloaded from the CRU web site today.> t9510<- ts(c(0.275, 0.137, 0.352, 0.548, 0.297, 0.271, 0.408, 0.465, 0.475, 0.447, 0.482, 0.425, 0.402, 0.325, 0.443, 0.476), start=1995)> library(nlme)> confint(gls(t9510 ~ time(t9510), cor=corARMA(p=1,q=0)))                    2.5 %     97.5 %(Intercept) -48.929568004 4.37230179time(t9510)  -0.001989347 0.02462824As shown, the 95%-confidence interval for the slope of the line includes 0. Hence the trend is not significant.Jun 10, 2011 at 7:06 PM | Douglas J. Keenan"

It looks to me that he has tried to get over this tricky problem by assessing it at the 97.5% confidence level and saying that he is assessing it at the 95% level! However I am by no means a statistician so I can't feel 100% sure. If anyone out there has this expertise, and is able to post a rebuttal to Keenan on our site, then I think that would be a useful intervention, and again much appreciated.

I won't have much chance to check comments on this thread today unfortunately as out and about but will be able to let comments through. Many thanks