Robert Way and the SKS Secret Society

I’ve looked closely at the evidence and the “array of evidence” is not as convincing as one would think. Many of the studies use the same old data e.g. bristlecones and therefore do not provide independent support. I think that it’s really too bad that specialists have failed to ensure that subsequent studies used independent data, given the criticisms. What is the “array of evidence” that you have in mind? Again, I do not take the position that good arguments are impossible.

Robert Way
Posted Nov 20, 2013 at 1:51 AM | Permalink

“What is the “array of evidence” that you have in mind? Again, I do not take the position that good arguments are impossible.”

I think the melt rates observed on many ice caps (in particular in the Canadian Arctic) provide fairly strong evidence that the warmth in that portion of the Arctic was much lower during the MWP – as does some of the work by Miller. The paper by Shi et al (2013) is fairly convincing as to at least the last 1,000 years in the Northern Hemisphere. I am actually surprised that paper has not been discussed here since it aims at dealing with many of the criticisms of paleoclimate research.

They use 45 annual proxies which are all greater than 1,000 years in length and all have a “demonstrated” temperature relationship based on the initial authors interpretations. Furthermore they use three different reconstruction methods (CPS, EIV and PC10+AR2). They also test for the impact of dendro versus non-dendro and compare their results with climate model simulations.

Shi et al (2013). Northern Hemisphere temperature reconstruction during the last millennium using multiple annual proxies. Climate Research, 56: 231-244.

In the past e.g. here, I’ve commented favorably on Miller’s work and observed that was “a line of argument that, in my opinion, might well be used to argue that modern warmth has surpassed MWP warmth. Assembling such facts would be far more persuasive to me than multiproxy varvology with upside down data.” This seems to offer a better prospect of convincing evidence than a multiproxy reconstruction using Miller’s data upside-down, as PAGES2K Arctic did. The incorporation of lake sediment data into multiproxy composites seems fraught with problems to me. Having said that, I thought that there is much very sensible discussion of lake sediment in Baffin Island, which I read recently. Shi et al 2013 is a relatively recent study and I haven’t parsed it. Perhaps it is more convincing than its predecessors. I certainly don’t preclude the possibility that the Modern Warm Period is warmer than the Medieval Warm Period.

I should clarify that I simply repeated what was listed as criterion in the paper – I did not check to ensure the authors initial interpretations regarding temperature signal were retained (rightly or wrongly). During my read I was more interested in examining the differences between the reconstruction methodologies (EIV, CPS, PCA).

Robert, specialists in this field have placed far too much importance on complicated multivariate methods, in part, I suspect, because they tend to be outdoorsy, rather than mathematical, and do not have intuitive understanding of the underlying linear algebra, a topic that I’ve written on from time to time. If there is a consistent “signal” in the data, it emerges with simple weighted-averaging methods. More complicated methods run the risk of heavily weighting some series, flipping others. People who use “complicated” methods also tend to pay less attention to defects in the data e.g. Tingley and Huybers’ ludicrous inclusion of the contaminated portion of the Tiljander data, long after it was known to be contaminated. The larger issue here is more the continued passing-off of Graybill bristlecone data used in Mann et al 1998-99 as well as Mann et al 2008 in a supposedly “independent” study, as much as the (almost certain) incorrectness of their assertions of having carried out significance tests on local temperature.