Responses to McShane and Wyner

Gavin Schmidt and Michael Mann

Readers may recall a flurry of excitement in the blogosphere concerning the McShane and Wyner paper in August. Well, the discussions on the McShane and Wyner paper in AOAS have now been put online. There are a stunning 13 different discussion pieces, an editorial and a rebuttal. The invited discussions and rebuttal were basically published ‘as is’, with simple editorial review, rather than proper external peer review. This is a relatively unusual way of doing things in our experience, but it does seem to have been effective at getting rapid responses with a wide variety of perspectives, though without peer review, a large number of unjustified, unsupportable and irrelevant statements have also got through.

A few of these discussions were already online, i.e. from Martin Tingley, Schmidt, Mann and Rutherford (SMR), and one from Smerdon. Others, including contributions from Nychka & Li, Wahl & Ammann, McIntyre & McKitrick, Smith, Berliner and Rougier are newly available on the AOAS site and we have not yet read these as carefully yet.

Inevitably, focus in the discussions is on problems with MW, but it is worth stating upfront here (as is also stated in a number of the papers) that MW made positive contributions to the discussion as well – they introduced a number of new methods (and provided code that allows everyone to try them out), and their use of the Monte Carlo/Markov Chain (MCMC) Bayesian approach to assess uncertainties in the reconstructions is certainly interesting. This does not excuse their rather poor framing of the issues, and the multiple errors they made in describing previous work, but it does make the discussions somewhat more interesting than a simple error correcting exercise might have been. MW are also to be commended on actually following through on publishing a reconstruction and its uncertainties, rather than simply pointing to potential issues and never working through the implications.

The discussions raise some serious general issues with MW’s work – with respect to how they use the data, the methodologies they introduce (specifically the ‘Lasso’ method), the conclusions they draw, whether there are objective methods to decide whether one method of reconstruction is better than another and whether the Bayesian approach outlined in the last part of the paper is really what it is claimed. But there are also a couple of very specific issues to the MW analysis; for instance, the claim that MW used the same data as Mann et al, 2008 (henceforth M08).

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