This may be old news to many that read my posts, but a comment on one of my recent posts has made me think that I should try to address the claim that the Hockey Stick has been debunked. The basic story is that Mann, Bradley & Hughes published a paper in 1998 called Northern Hemisphere Temperatures During the Past Millenium: Inferences, Uncertainties and Limitations. The paper presented reconstructions of the temperature history for the last 1000 years that indicated that temperatures were reasonably constant up until the mid 1800s and then rose sharply. The shape of the temperature profile was, therefore, referred to as a Hockey Stick.
In 2005, Stephen McIntyre and Ross McKitrick published a paper called Hockey Sticks, Principal Components, and Spurious Significance. In this paper they conclude by saying
…., the effect of the transformation is so strong
that a hockey-stick shaped PC1 is nearly always generated
from (trendless) red noise with the persistence properties of
the North American tree ring network.
What they are suggesting is that the analysis used by Mann, Bradley & Hughes can produce hockey stick shaped temperature reconstructions even if the data is simply random red noise. The conclusion is, therefore, that the Mann, Bradley & Hughes analysis is flawed and that the Hockey Stick is not real.
Now, this is all rather odd. Partly because the instrument record shows that surface temperatures have indeed risen dramatically in the last 100 years or so, and partly because numerous other studies have reproduced the hockey stick profile. One explanation I have heard is that McIntyre & McKitrick did indeed produce hockey sticks from their red-noise data, but only when – by chance – their red-noise data had an underlying hockey stick.
The comment I referred to at the beginning of this post was made by caerbannog666 and provides a slightly different explanation. You can read caerbannog666’s comment here. What is claimed is that McIntyre & McKitrick produced their red-noise by using the data from Mann, Bradley & Hughes, but forgot to de-trend, or remove the underlying hockey stick shape. Therefore, the reason their analysis produced hockey sticks was not because the Mann, Bradley & Hughes analysis was flawed, but because there was a hockey stick profile in their data. This certainly seems at least partly consistent with what McIntyre & McKitrick did, as they say in their paper
We generated the red noise network for Monte Carlo
simulations as follows. We downloaded and collated the
NOAMER tree ring site chronologies used by MBH98 from
M. Mann’s FTP site and selected the 70 sites used in the
Caerbannog666 provides a link to the code used by McIntyre & McKitrick to do their analysis. I haven’t understood the code completely, but it has two main parts. The first part has the various functions, the second is the Narrative portion to generate figures and statistics. It does appear as though the part of the code where the Mann, Bradley & Hughes data is read-in does not do anything to remove the underlying hockey stick. There is a detrend function in part one, but it’s not clear if or where this is used (if at all).
Now, maybe this has already been addressed somewhere else and everyone already knows whether McIntyre & McKitrick properly detrended their data or not. Also, I’ve misunderstood how other people’s codes work on many occasions in the past, so I don’t want to claim that McIntyre & McKitrick have made some kind of fundamental mistake. However, this does seem like something that could be addressed very easily. Either they removed the underlying hockey stick when they produced the red-noise data that they used to test the Mann, Bradley & Hughes analysis, or they didn’t.
So, my basic question to either Stephen McIntyre or Ross McKitrick is did you properly remove any underlying hockey stick profile from the data you used to produce the red-noise that you used in your 2005 paper. If so, my next question is where in the code is this procedure applied and how does it work. Fairly straightforward questions that should be easy enough to answer. Given that the debunking of the hockey sticks is one of the mainstays of the typical skeptic’s argument, it would seem that clarifying this would be very important.