There are some basic truths everyone should be able to agree to. In discussions of climate science, one of those truths is the greenhouse effect is real. I’d like to discuss what I believe should be another.
A few days ago I came across a post at the (formerly known as) wottsupwiththat blog. I was disturbed to see this:
So, I’m no longer interested in discussions about aspects that are largely indisputable. The rise in atmospheric CO2 is anthropogenic. There is virtually no doubt. Our current overall warming is also anthropogenic. Again, there is virtually no doubt. Michael Mann’s Hockey Stick has not been debunked, despite what people might say (McIntyre & McKitrick 2005 has numerous easily explained issues). Exactly where to draw the line with respect to the science is trickier, as there aspects that are uncertain and I certainly don’t even want to prevent discussion about those aspects that are certain. I just don’t want comment threads diverted into lengthy exchanges about something that is largely undisputed.
The first notion is relatively indisputable. I’m not sure what the author means by “overall warming is also anthropogenic” for the second notion. I’m going to assume author means humans have contributed some amount of warming as that is indisputable. The third notion is where my problem lies.
Michael Mann’s hockey stick has been the subject of a great deal of discussion, and it seems the author is simply dismissing all of that with a wave of his hand. Even worse, he says “McIntyre & McKitrick 2005 has numerous easily explained issues,” but he doesn’t say what those issues are. He doesn’t provide a link to a discussion of them. He doesn’t provide a reference for the claim. Even worse, he doesn’t explain why we should only care about that one paper when multiple papers were published criticizing Mann’s hockey stick.
Worse than that? McIntyre & McKitrick published two such papers in 2005. The author of that post refers to one but doesn’t distinguish which. That flawed reference, combined with his failure to mention any other paper, seems to suggest he doesn’t know multiple papers exist. I’m at a loss to explain the paragraph otherwise. Regardless, I thought it’d be worthwhile to seek out the author’s previous refutations of McIntyre and McKitrick’s work. A search of his site pulled up this post from five months ago. I read it, saw the author had little knowledge of the material he discussed in it, and today I wrote up a response. Unfortunately, when I went to submit it, I was given an error by his blog software. It seems the post cannot be commented on now (perhaps due to its age). As such, I’m posting what I wrote here:
This post unfortunately doesn’t examine anything in depth. To address that, I’ll attempt to. To begin, I’ll answer the question asked of Steve McIntyre and/or Ross McKitrick:
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
This question is poorly phrased. Whether or not the NAOMER series ought to have been detrended prior to being used to calculate red noise profiles is a matter one can dispute. Consider, for example, this post at Real Climate. It discusses the use of pseudoproxies created via examining the red noise profiles of the NAOMER series used by McIntyre and McKitrick. Not only do the authors not say it is necessary to detrend the series first, Michael Mann himself specifically promotes calculations as being done without such a step (in several inline responses). If the lead author of a paper promotes a process, it is difficult to see why critics of the paper should have their criticisms disputed based on the use of that process.
With that caveat in place, I can answer the question as, “No.” However, I can go beyond that. Critics of the hockey stick are often faulted for not examining the impact of the supposed flaws they find. To address this, we can examine the impact using a different red noise profile would have. Fortunately, it’s already been done. Take a look at this comment from Nick Stokes on his post criticizing the Wegman Report for how it critized Mann’s hockey stick. Nick Stokes is a frequent defender of the hockey stick, the post was defending the hockey stick, and he still acknowledges “the MBH tendency to make PC1 HS-shaped.” Another user posted:
I’ve put up plots of runs for AR1 rho=0.1 and AR1 rho=0.0001 (at the same googlsites page linked to by Nick). These are for 2000 rather than 10,000 PC1’s, to save time.
The random samples from the results of the MBH method contain many hockeysticks (over 50%). The hockey-sticks are more pronounced for rho=0.1, but also present for rho=0.0001.
The point this user was making is no matter what red noise profiles one uses, the result is the same – the MBH PCA methodology mines for hockey sticks. That is true independent of whatever noise MM may have used.
I also wrote a follow-up comment which addresses the issue of Mann’s hockey stick more generally. I feel the position it advances is unremarkable, and it should be something everyone can agree to. I think it is a basic truth people need to accept in order to advance discussions:
Now then, MBH’s PCA methodology did not create the hockey stick out of nothing. When it mines for a hockey stick, it merely looks for data which has something of a hockey stick within it. It then gives that data extreme weight, causing the results to be a hockey stick. What this means is whether it be red noise or the NAOMER tree ring series, finding a hockey stick requires there be a hockey stick somewhere in the data.
The issue is not whether or not some data shows a hockey stick. The issue is whether or not the results are representative of the data being examined. In the case of MBH’s hockey stick, they are not. Mann himself has acknowledged this in regard to MBH98 in his recent book (page 51):
The tests revealed that not all of the records were playing an equal role in our reconstructions. Certain proxy data appeared to be of critical importance in establishing the reliability of the reconstruction–in particular, one set of tree ring records spanning the boreal tree line of North America published by dendroclimatologists Gordon Jacoby and Rosanne D’Arrigo.
The records he refers to are the NAOMER tree ring series he used. These are the same series MM claim are responsible for the hockey stick. MM claim Mann’s hockey stick wouldn’t have existed without those series, contrary to MBH’s paper which says:
On the other hand, the long-term trend in NH is relatively robust to the inclusion of dendroclimatic indicators in the network
Not only does is the MBH hockey stick not relatively robust to the inclusion of tree ring data, it is entirely dependent upon a small amount of tree ring data – a fact Mann himself has basically acknowledged.
The original hockey stick is dependent entirely upon a small amount of tree ring data. Of the 70 NAOMER series which extended back to the period in question, approximately 20 contribute to the hockey stick. Remove those 20 series, and the hockey stick vanishes. Put them back in, and it reappears. Those ~20 series are responsible for the iconic hockey stick, and the hundreds of others were mostly irrelevant.
One can ignore the topic of red noise if one wants. That demonstration was used merely to show how MBH’s PCA methodology used a small amount of series to create results not representative of the data in general. You can accomplish the same by just removing the data MBH gave undue weight to. The MBH authors did this themselves, and they found the same thing.
That just leaves the question, was it right to base our understanding of northern hemispheric temperatures on basically one set of tree ring data? Was it right for the IPCC to heavily promote such an understanding? I say no.
If people could agree to this, we could try to move on. We could try to discuss what paleoclimatology has done since Mann’s hockey stick. We could discuss criticisms of subsequent temperature reconstructions and whether or not those criticisms are sufficient to call the mainstream position into question. We could make progress and come to understandings.
What I’ve said about MBH’s methodology is beyond dispute. It is easier to verify than the radiative physics behind the fact CO2 emissions cause warming. There is not a single technical, or even coherent, argument which disputes the fact Mann’s hockey stick was dependent entirely upon a small amount of tree ring data.