The Hockey Stick (MBH98)
My story from believer to skeptic – part 3
You might see Part 1 or
Part 2 first if you haven’t already.
In Part 2 I explained I started to realize that the global warming alarmism was just a gross exaggeration, not always backed by the observations. But the alarmist side still had a convincing argument. The last hurdle to take was the temperature chart of the last 1000 year. I came to know the name of this chart: The Hockey Stick. It was made by Michael Mann, Raymond Bradley and Malcolm Hughes in 1998 (MBH98) and was extended in 1999 (MBH99). It represented temperatures of the Northern Hemisphere over the last 1000 years. It showed a slowly rising of the temperature (the shaft) until the last -let’s say 100 years- when it went completely through the roof (the blade).
This chart was been found everywhere I looked for proof of human fingerprint of the warming due to CO2. I still was really naive at that time and I believed this graph was correct because it popped up about everywhere. How could this be incorrect after so many people eyeballing it? I compared it to the system of Open Software in which bugs gets removed by maximum exposure to many people that get access to it. The more people look at it, the quicker the bugs can be found and eliminated. So my thoughts were, the more that Hockey Stick figure gets reviewed, if there were errors in it, the quicker they would be found.
It was confusing. If this graph really was true, then my new understanding about climate didn’t even matter, then there was a very good reason for sounding the alarm. It was clear for all to see. In the time frame in which man was developing rapidly, temperatures went through the roof. It couldn’t be more clear.
In the meanwhile it became January 2009, about three months after I started my quest. At that time I became a regular visitor of a site called ClimateAudit. It is run by a Canadian mathematician Stephen McIntyre. I didn’t realize it, but he was an important factor in the investigation of the hockey stick graph. Together with Ross McKitrick (a Canadian environmental economist of the University of Guelph) he investigated the graph and they found things didn’t add up.
The Wegman report
One day, when I visited the blog, I checked the links bar on the left in stead of directly start reading the articles. There I stumbled on a link to the Wegman Report (left link bar, under “Links”). From previous searches I remembered vaguely that it had something to do with the Hockey Stick. I downloaded the report and started to read. I was baffled. The more I read it, the more I realized the Hockey Stick probably was based on faulty assumptions, bad statistics and probably a too close related group of scientists. This was the final drop in a bucket almost full.
To come back to the report. Edward Wegman is a statistician (Center For Computational Statistics, George Mason University) and he made this report for U.S. Congress in 2006. Some issues of the many parts that shook me (my bold):
The controversy of Mann’s methods lies in that the proxies are centered on the mean of the period 1902-1995, rather than on the whole time period. This mean is, thus, actually decentered low, which will cause it to exhibit a larger variance giving it preference for being selected, as the first principal component. The net effect of this decentering using the proxy data in MBH98 and MBH99 is to produce a “hockey stick” shape. Centering the mean is a critical factor in using the principal component methodology properly. It is not clear that Mann and associates realized the error in their methodology at the time of publication. Because of the lack of full documentation of their data and computer code, we have not been able to reproduce their research. We did, however, successfully recapture similar results to those of MM [McIntyre & McKitrick]. This recreation supports the critique of the MBH98 methods, as the offset of the mean value creates an artificially large deviation from the desired mean value of zero.
After MBH99, Stephen McIntyre and Ross McKitrick [MM03] published their critique of the 1998 paper, citing calculation errors, unjustified truncation or extrapolation of source data, obsolete data, geographical location errors and incorrect calculation of principal components. They also claimed that using the MBH98 methodology and the Northern Hemisphere average temperature index for the period 1400-1980 shows that temperatures in the 15th century exceeded those of the late 20th century. In particular, they claim that MBH98’s incorrect usage of PCA alone resulted in the well-known “hockey stick” shape.
Wow, this was heavy! The hockey stick didn’t seem to be withstand scrutiny well. As far as I could understand it, the uptick at the end was not derived from the data itself, but was formed from an incorrect usage of methodology, combined with the use of a proxy that doesn’t seem to be a good proxy for temperature in the first place. Stephen McIntyre and Ross McKitrick went even further and tested the methodology itself. They took red noise (a kind of random data) and combined it with the Bristlecone data. They found that this created hockey sticks in 99% of the cases. Oops.
This story of the investigation of the hockey stick is broader than the Wegman report. But this report was the trigger for looking into the issue in more detail. The best summery of this story is written by Marcel Crok in NatuurWetenschappen & Techniek: a very clear and well researched NWT article in pdf format. Best to look at this pdf before continue, in order to be able to situate the impact it had on me.
Even more background information (on this page is a link to a pdf file with the background information).
Finally, the Hockey Stick Project page with the complete time line and responses to criticism on their investigation.
Why this report (and the papers of McIntyre and McKitrick on the Hockey Stick) had such an impact on me?
- It showed that my assumption that the graph was properly eyeballed didn’t hold. It took a lot of time and effort of at least one person (and probably three persons or more) to get hold of the methods and data to be able to review it. It took me by surprise that the information that proved anthropogenic global warming was not organized or documented. This didn’t make much sense to me. How could that very important data not being available for all to investigate? Is this how scientists behave when they have crucial data that is important for explaining “the most important problem of human kind”!?!? The eyeballing I presumed was only the peer review that was apparently done within a small group of closely related people. We should expect more scrutiny of data that affect policy decisions.
- The graph depended heavily on statistics, but when statisticians reviewed this paper, they found many errors in it, not detected by the (much celebrated) peer-review process. This got me thinking about what this peer review was all about. In this case it definitely wasn’t the gold standard it was told to be.
- It was the first time that I noticed the political side behind climate science (the graph was prominent in the 2001 IPCC report).
The final result is that I am not much impressed anymore with someone showing a hockey stick result as proof of global warming and there have been many since.
And hey, we know the temperatures in the 20th century went up. What’s the big deal? Sure, temperatures went up in last century, but that was not the claim. The claim was that the temperatures of the 1990s were the highest of the last 1000 years, but this doesn’t follow from the data.
I couldn’t see this in the past, because I didn’t look at the data and just believed what others told me (others who obvious didn’t look at the data either). This is a viscous circle. People read that CAGW is true, don’t check the data and pass the message on. In this way it looks as if this is an universal truth, because the same message is mentioned everywhere.
Stephen McIntyre and his blog certainly had a huge influence on me. What influenced me most was the expression to check things oneself and in the end this is what I began to do. That was one of the reasons why I started this blog and adopted this blog name.