It depends on exactly what you mean by “the hockeystick”. The NAS conclusion was carefully worded to be ambiguous.

The scientifically supportable position is that, to the extent that global temperature history can be determined from proxies, there was a warm period about 1000 years ago called the Medieval Warm Period in which temperatures appear to be the same or slightly higher than today, followed by a cold period popularly known as the Little Ice Age, followed by the modern warm period.

It is perfectly true that the modern warm period is probably the warmest in 400 years, because that puts us back in the middle of the LIA. It is plausible that the modern period is slightly warmer than the MWP, because the error bars are so large on the reconstruction of the past that we can’t tell if the earlier warm period was as warm as it appears. The conclusion you seem so insistent on is one that, when parsed precisely, sceptics would very likely agree with: that we don’t know.

We can’t reconstruct temperatures that accurately, so we don’t know that the MWP was warmer, so it is plausible that it is not. And there are indeed (flawed) studies in existence that support the idea that it wasn’t.

It’s a classic politician’s answer, that doesn’t mean what you seem to think it means.

But with world views in such violent collision, I’m impressed that we’ve got as far as we have. I don’t think there’s any more to be gained from parsing the ambiguities of the NAS.

Oh, and Nullus #56: your highlighted point about the weakness of tree ring proxies points to the wisdom of the CRU scientists disregarding the flubby data that they produce–as they announced publicly they would do in the peer-reviewed 1998 Nature article, later referred to shorthandedly as “the Nature trick to hide the decline”.

Deny, deny, deny.

“This conclusion has subsequently been supported by an array of evidence that includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators, such as melting on ice caps and the retreat of glaciers around the world, which in many cases appear to be unprecedented during at least the last 2,000 years. Not all individual proxy records indicate that the recent warmth is unprecedented, although a larger fraction of geographically diverse sites experienced exceptional warmth during the late 20th century than during any other extended period from A.D. 900 onward.
Based on the analyses presented in the original papers by Mann et al. and this newer supporting evidence, the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium. The substantial uncertainties currently present in the quantitative assessment of large-scale surface temperature changes prior to about A.D. 1600 lower our confidence in this conclusion compared to the high level of confidence we place in the Little Ice Age cooling and 20th century warming. Even less confidence can be placed in the original conclusions by Mann et al. (1999) that “the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium” because the uncertainties inherent in temperature reconstructions for individual years and decades are larger than those for longer time periods and because not all of the available proxies record temperature information on such short timescales”

Deny, deny, deny…

Wow, I can’t believe this is so hard to understand. You guys are trying to make the case that the NAS didn’t support Mann.

Let me quote NAS’s fundamental finding one more time:

[Mann's basic] conclusion has subsequently been supported by an array of evidence….

You can try to count the angels dancing on the head of a pin as long as you want, but that is their conclusion.

So does that mean you’re admitting to MBH98 and 99 being flawed? That we should throw them all away? Because it would be really nice to get that point out of the way, in black and white, before we move on to all the *other* reconstructions.

The NAS report did indeed cite a number of other reconstructions that supported the conclusion. Unfortunately, they failed to note that most of them used the exact same methods they had just criticised, and said shouldn’t be used. In particular, the use of the strip-bark proxies.

But if you was to throw out every reconstruction that used strip-bark Bristlecones/Foxtails, every reconstruction that used Yamal, or the outdated version of the Polar Urals series, and every reconstruction that incorporated series upside down, then I would agree that we were getting somewhere. I’d also like you to take out every series that either cuts off, or splices on instrumental data post-1960 to cover up the divergence problem – something the NAS panel didn’t address, because it doesn’t apply to MBH but does to a couple of the others. We’ll take a look at what’s left.

Let me know when climate science has done that, will you?

But here’s the money shot:

[Mann's basic] conclusion has subsequently been supported by an array of evidence….

And there you have it. At the end of the day, that is the only thing that’s important. His graph isn’t. His methodology isn’t. His papers aren’t. Throw them all away if you want. Send Mann to jail if you want. It doesn’t matter.

Only one thing matters: That there has been a sudden, severe, and, by all available evidence, very unusual warming since 1975 or so. That’s the critical fact, and you don’t need Mann for that. It’s supported by “an array of evidence” and research that he had nothing to do with. This is the essential fact that NAS grasps and that you guys seem unable to. You can nitpick about PCA all you want. It doesn’t change what’s happened.

You’re obsessing about the shape of one blade of grass in a forest.

“in my opinion the Panel adopted the most critical position to MBH nowadays possible. I agree with you that it is in many parts ambivalent and some parts are inconsistent with others. It would have been unrealistic to expect a report with a summary stating that MBH98 and MBH99 were wrong (and therefore the IPC TAR had serious problems) when the Fourth Report is in the making. I was indeed surprised by the extensive and deep criticism of the MBH methodology in Chapters 9 and 11.”

For periods prior to the 16th century, the Mann et al. (1999) reconstruction that uses this particular principal component analysis technique is strongly dependent on data from the Great Basin region in the western United States.
[i.e. Stripbark Bristlecones.]

Regarding metrics used in the validation step in the reconstruction exercise, two issues have been raised (McIntyre and McKitrick 2003, 2005a,b). One is that the choice of “significance level” for the reduction of error (RE) validation statistic is not appropriate. The other is that different statistics, specifically the coefficient of efficiency (CE) and the squared correlation (r2), should have been used (the various validation statistics are discussed in Chapter 9). Some of these criticisms are more relevant than others, but taken together, they are an important aspect of a more general finding of this committee, which is that uncertainties of the published reconstructions have been underestimated.

* The observed discrepancy between some tree ring variables that are thought to be sensitive to temperature and the temperature changes observed in the late 20th century (Jacoby and D’Arrigo 1995, Briffa et al. 1998) reduces confidence that the correlation between these proxies and temperature has been consistent over time. Future work is needed to understand the cause of this “divergence,” which for now is considered unique to the 20th century and to areas north of 55°N (Cook et al. 2004).
* For tree ring chronologies, the process of removing biological trends from ring-width data potentially obscures information on long-term changes in climate.
*Temperature reconstructions for periods before about A.D. 1600 are based on proxies from a limited number of geographic regions, and some reconstructions are not robust with respect to the removal of proxy records from individual regions (see, e.g., Wahl and Ammann in press). Because the data are so limited, different large-scale reconstructions are sometimes based on the same datasets and thus cannot be considered as completely independent.

Large-scale surface temperature reconstructions demonstrate very limited statistical skill (e.g., using the CE statistic) for proxy sets before the 19th century (Rutherford et al. 2005, Wahl and Ammann in press).

While “strip-bark” samples should be avoided for temperature reconstructions, attention should also be paid to the confounding effects of anthropogenic nitrogen deposition (Vitousek et al. 1997), since the nutrient conditions of the soil determine wood growth response to increased atmospheric CO2 (Kostiainen et al. 2004).

—
And from the congressional committee:

CHAIRMAN BARTON. I understand that. It looks like my time is expired, so I want to ask one more question. Dr. North, do you dispute the conclusions or the methodology of Dr. Wegman’s report?
DR. NORTH. No, we don’t. We don’t disagree with their criticism. In fact, pretty much the same thing is said in our report. But again, just because the claims are made, doesn’t mean they are false.
CHAIRMAN BARTON. I understand that you can have the right conclusion and that it not be–
DR. NORTH. It happens all the time in science.
CHAIRMAN BARTON. Yes, and not be substantiated by what you purport to be the facts but have we established–we know that Dr. Wegman has said that Dr. Mann’s methodology is incorrect. Do you agree with that? I mean, it doesn’t mean Dr. Mann’s conclusions are wrong, but we can stipulate now that we have–and if you want to ask your statistician expert from North Carolina that Dr. Mann’s methodology cannot be documented and cannot be verified by independent review.
DR. NORTH. Do you mind if he speaks?
CHAIRMAN BARTON. Yes, if he would like to come to the microphone.
MR. BLOOMFIELD. Thank you. Yes, Peter Bloomfield. Our committee reviewed the methodology used by Dr. Mann and his coworkers and we felt that some of the choices they made were inappropriate. We had much the same misgivings about his work that was documented at much greater length by Dr. Wegman.