Authors of new hockey stick paper backtrack on claims
Almost one month ago authors of a new paper claimed to have found evidence that confirmed the now famous Michael Mann "hockey stick" graph. The paper was heralded in numerous blogs and newspapers as evidence that the criticisms laid against Mann were unwarranted. Articles such as this one in the Atlantic were common:
http://www.theatlantic.com/technology/archive/2013/03/were-screwed-11-000-years-worth-of-climate-data-prove-it/273870/
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Back in 1999 Penn State climate scientist Michael Mann released the climate change movement's most potent symbol: The "hockey stick," a line graph of global temperature over the last 1,500 years that shows an unmistakable, massive uptick in the twentieth century when humans began to dump large amounts of greenhouse gases into the atmosphere. It's among the most compelling bits of proof out there that human beings are behind global warming, and as such has become a target on Mann's back for climate denialists looking to draw a bead on scientists.
Now it's gotten a makeover: A study published in Science reconstructs global temperatures further back than ever before -- a full 11,300 years. The new analysis finds that the only problem with Mann's hockey stick was that its handle was about 9,000 years too short.
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This past weekend, after weeks of criticism and careful review of the data used by the paper, the authors have been forced to backtrack on their claims and admit the following:
Our global paleotemperature reconstruction includes a so-called “uptick” in temperatures during the 20th-century. However, in the paper we make the point that this particular feature is of shorter duration than the inherent smoothing in our statistical averaging procedure, and that it is based on only a few available paleo-reconstructions of the type we used. Thus, the 20th century portion of our paleotemperature stack is not statistically robust, cannot be considered representative of global temperature changes, and therefore is not the basis of any of our conclusions.
How a paper containing such misleading graphs and conclusions could make it past peer review in a journal as prestigious as Science is a question that must be answered. The climate change research community needs to address this issue quickly and forcefully to demonstrate that it engaging in science, not activism. This article by Andrew Revkin is a good start:
http://dotearth.blogs.nytimes.com/2013/03/31/fresh-thoughts-from-authors-of-a-paper-on-11300-years-of-global-temperature-changes/
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...there’s also room for more questions — one being how the authors square the caveats they express here with some of the more definitive statements they made about their findings in news accounts.
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= new reply since forum marked as read
Oh, wait, there is none. Never mind. 
(P.S. And notice that RealClimate didn't have a problem with the revisions, either. IMO, that's usually a good sign.....And I'm sure if they had been actually forced to say these things, something would have come up by now.)
If the authors and the journal print a correction with the last 100 years of data (data that they admit is "is not statistically robust" being left off the graph then I will agree with you. It will be interesting to see which scientists call for this action and which ones remain silent.
Here's what they've said in this Q&A:
A: Our global paleotemperature reconstruction includes a so-called “uptick” in temperatures during the 20th-century. However, in the paper we make the point that this particular feature is of shorter duration than the inherent smoothing in our statistical averaging procedure, and that it is based on only a few available paleo-reconstructions of the type we used. Thus, the 20th century portion of our paleotemperature stack is not statistically robust, cannot be considered representative of global temperature changes, and therefore is not the basis of any of our conclusions. Our primary conclusions are based on a comparison of the longer term paleotemperature changes from our reconstruction with the well-documented temperature changes that have occurred over the last century, as documented by the instrumental record. Although not part of our study, high-resolution paleoclimate data from the past ~130 years have been compiled from various geological archives, and confirm the general features of warming trend over this time interval (Anderson, D.M. et al., 2013, Geophysical Research Letters, v. 40, p. 189-193; http://www.agu.org/journals/pip/gl/2012GL054271-pip.pdf).
Yes, we know that global temperatures have gone up in the past century, from direct measurements, not from proxies. This study was not designed to study that time period. Check the 3 posts on the Tamino blog that discussed this, before that Q&A from Marcott, that the piece also links to:
reconstruction was much larger than in their RegEM reconstruction, and that they had expressed doubt about its robustness. The large uptick at the end (in 1940) is larger than indicated by the instrumental data — another reason to doubt its reality. Let me tell you my opinion why this difference exists. I could be mistaken, but this is what I think.
As I hinted earlier, it has to do with proxy drop-out over time. All 73 of their proxies cover the time span 5500 to 4500 BP (calendar years -3550 to -2550), but as time marches forward the number of proxies which still have data dwindles, especially toward the end of the reconstruction (1940) by which time only 18 proxies remain.
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That is what they said three months AFTER the paper came out and their methodology had been torn to shreds but critics.
More importantly, did you even read the third Tamino post ("Regional Marcott" you linked to? It supports exactly what I claimed in the OP--that the methodology in the paper exaggerates the 20th century uptick and makes the rise in temperatures in the 20th century look unprecedented, when actually they are not:
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