The question dear bunnies, is why does this figure from Tamino's post on change have the answer to what is going on in the flat new paper on proxy deconstruction by McShane and Wyner (ps there are lots of hints in the comments at Open Mind but here is another one, look at the figure and then remember that McShane and Wyner are claiming that noise gives a better match to the global temperature series than proxys) Also take a look at the comments at Policy Lass
Eli's answer later tonight.
UPDATE: Eli does have a day job folks......
When you calibrate, respectable Rabett's want the largest spread of the variable calibrated against as possible. M&W calibrated proxies that respond to regional changes against the GLOBAL temperature record. If you look at Tamino's figure, for about 80 of ~120 years (M&S only go to 2000, there ain't a lot of proxies that go to 2010), a flat line is about the best description of what happened. This covers the period from ~1880 - 1920 and ~ 1940 - 1980. In such a situation, random noise is the best description of the variation. So especially if you hold out the last 30 years and prattle on about, bunnies find that random noise about a straight line provides the best fit, which is what the boys find, and of course it does not capture the sharp rise in the last30 year period. As they say,
In other words, our model performs better when using highly autocorrelated noise rather than proxies to predict temperature. The real proxies are less predictive than our "fake" data.Since the proxies are affected by the local temperatures (and precipitation and some other things that are all local) and the local temperatures varied much more strongly than the global in most cases, and surely for those cases where the proxies vary strongly, this is kindergarten work. Trivially, this procedure underestimates the response of the proxies to the temperature over long periods and exaggerates the error projected back to the year dot. You are fitting noisy data to a straight line to find a slope? C'mon. QED
Tim Lambert has more, and, as Eli said, the comments at Policy Lass and Tamino's are fine. Judith Curry is sitting on the sticky wicket at Kloor's and the unusual suspects, well, there is a reason they are unusual.
UPDATE: Martin Vermeer says it more clearly at Deltoid
Evidently there will be a comments on this paper at the journal (they select a few people to comment). Hopefully, much of the back and forth, with the cheerleading and booing edited out will be picked up.
My explanation at link for why the M&W reconstruction is erroneous, was a little too simple. It's the Wabett who gets it completely right: the fundamental error is calibration only against a hemispheric average, when local data -- the 5x5 degree grid cells of instrumental data as used by Mann et al. -- provide a so much richer source of variability -- i.e., signal -- to calibrate against.
It is this poor signal/noise ratio that helps the calibration pick up spurious low vs. high latitude temp difference "signal", which in the reconstruction interacts with the Earth axis tilt change effect.
What stands is the observation that doing the calibration against the instrumental PC1 (instead of hemispheric average) will give you back pretty exactly the genuine Mann stick(TM) even in spite of this.