This is a repost from Eduardo Zorita’s blog, regarding a paper produced by Bo Christiansen which analyzed variance loss in climate reconstructions. It’s a science post so keep all comments/questions on that topic or face the red heat laser of doom.
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Mann 07 made the claim that RegEM didn’t create variance loss and alleged proof using pseudoproxies. This was of course ‘proven’ false here recently with a few simple posts and the ‘difference of opinion’ was identified in the artificially trendless noise added to the mannian pseudoproxies.
This is a very ‘hot’ field in climatology because the reasonable scientists have finally recognized the math issue that I found obvious literally within moments of reading my first hockey stick paper at CA. I’m not that smart BTW, so why is it that Mann can find every excuse to miss the point?
Anyway, I read the pre-print of this paper but if someone can send a non-paywall copy of the final version, I would appreciate it. There is a cool equation in the pre-print which would make a fun post by itself.
This paper again demonstrates what I consider the primary reason for unprecedentedness and repeatability of so many hockey stick proxy papers. Remember, the primary defense of the hockey sticks is that so many have reproduced the result. The reason is twofold. At CA Steve has focused on unique proxies – they are unique, here, we have focused on math.
BTW, I doubt any of these scientists are as skeptical of other AGW claims as some of us are so don’t attach some of the tAV fare to them. That doesn’t mean that they don’t do good, honest and open science - don’t lump their fine work in with the opinions of those of us who are outsiders.
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Posted by eduardo
Bo Christiansen from the Danish Meteorological Institute works actively on the development of statistical methods for climate reconstructions, a field of intense debate in the past few years. Hopefully we will enter a phase in which scientific debates remain .. well, in the scientific realm. Enjoy his post.
Anthropogenic emissions of greenhouse gases – in particular CO2 and methane – change the radiative properties of the atmosphere and thereby impose a tendency of heating at the surface of the Earth. In the past the Earths temperature has varied both due to external forcings such as the volcanic eruptions, changes in the sun, and due to internal variability in the climate system. Much effort has in recent years been made to understand and project man-made climate change. In this context the past climate is an important resource for climate science as it provides us with valuable information about how the climate responds to forcings. It also provides a validation target for climate models, although paleoclimate modelling is still in its infancy. It should be obvious that we need to understand the past climate variability before we can confidently predict the future.

Fig 1. Pseudo-proxy experiments with seven different reconstruction methods. The black curve is the NH mean temperature, the target which we hope the reconstructions will catch. But this is not the case: All reconstructions underestimate the pre-industrial temperature level as well as the amplitude of the low-frequency variability. Note that the reconstructions are very good in the last 100 years which have been used for calibration. The three panels differ in the strength of the variability of the target. From Christiansen et al. 2009.