There’s a paper out today (just published online) by J. C. Fyfe, N. P. Gillett, and F. W. Zwiers, called “Overestimated global warming over the past 20 years”. I’ve addressed this “pause in warming question” at this blog earlier, and the argument they make, based upon the Supplement to the article (which is not behind a payment), is predominantly statistical. The authors are well-known in IPCC circles and, statistically speaking, Zwiers is a co-author with von Storch with the good but somewhat dated book Statistical Analysis in Climate Research (which I own).
But, Judith Curry has commented on the article, and I’m sure it’s going to be a major feature of discussion with the latest IPCC report due out soon. (Added 16th September 2013: In case the reader is not familiar with Judith Curry, this is an example of what’s wrong with Curry’s kind of analysis.)
So, I’m buying a copy of the article, and will do an analysis, reporting here. What’s odd about the material in the Supplement, and I hope they address in the article, is the difference in methodology in apparently what Fyfe, Gillett, and Zwiers did, and what’s been done earlier, which hopefully they’ll contain in their references. I’m thinking specifically of:
- S.-K. Min, D. Simonis, A. Hense, “Probabilistic climate change predictions applying Bayesian model averaging”, Philosophical Transactions of the Royal Society A, 15 August 2007, 365.
- R. L. Smith, C. Tebaldi, D. Nychka, L. O. Mearns, “Bayesian modeling of uncertainty in ensembles of climate models”, Journal of the American Statistical Association, 104(485), March 2009.
I also think it odd that they claim they made no distributional assumptions in the derivation in their Supplement, which I find highly dubious. I mean, there are no explicit distribution assumptions made when you do linear least squares, but it’s provable that it is equivalent to a Gaussian model of errors.
Postscript: 30th August 2013, 12:56 EDT.
I am delving deeply into the techniques of this interesting meta-analysis, with kind help of Professor Francis Zwiers. Of course, anything I say or present here is my own technical responsibility, not his. I will probably write a white paper on this, sharing it with Professor Zwiers, and presenting highlights here.
Postscript: 31st August 2013, 09:52 EDT.
Jokimäki posts “Global warming … Still happening” at the SkepticalScience blog and indeed it is. Has to be, lest basic, 19th century-derived physics be violated, not to mention our engineering of spacecraft and semiconductors. It will be very interesting rationalizing the Rahmstorf (with Foster and Cazenave) kinds of projections he reports with this Fyfe, Gillett, and Zwiers paper. And a good chance to contribute to improving the statistical arsenal applicable to climate work. Right now I’m having a serious look at empirical likelihood techniques, as used in nested sampling and approximate Bayesian computation. (See, for instance, Professor Christian Robert’s talk, or Lazar, “Bayesian empirical likelihood”, Biometrika, 2003.)