FAQ 2005

FAQ 2005

What is the connection of the present studies to your original article in 2003?

The present articles build on the first article. In that article, we pointed out that there were serious problems with the data set in MBH98 and, in particular, with the tree ring principal component series. We also showed that quite different results could be obtained for the 15th century under reasonable assumptions using the MBH98 method.

Since then, and largely because of the effect of the original article, a great deal of new information about MBH98 has been made available. In July 2004, at the direction of Nature, Mann et al. published a Corrigendum, which included a voluminous archive on data and methods used in MBH98.

Earlier, Mann et al. made public the address for the data actually used in MBH98, rather than the address which they had previously provided us. The present articles reflect detailed study of this new material. In particular, we are now able to precisely diagnose the problems with the principal component series in MBH98, which previously were simply noted as being incorrect.

We characterized our first article as raising “audit issues” without co-operation from the original authors, it could not be a complete audit. In retrospect, the issues raised have proved to be very important. In MM03, we reported that we were unable to replicate the MBH98 principal component series. Given the importance of Mann’s PC methods, one would think that this replication would have been attempted by someone else.

In MM03, we were not in a position to fully diagnose the problems, but we are now. Also, the simple comparison of archived series versions to versions actually used revealed the unreported editing of the Gasp” series, which also had important consequences. This effect was not specifically analyzed in MM03, but was analyzed here. In short, we believe that the present articles are a definitive resolution of issues first raised in MM03.

Has Michael Mann accepted any part of your arguments?

There is surprising agreement between Mann and ourselves on the effect of differing assumptions on the NH temperature reconstruction – if the assumptions are specified exactly. For example, both of us get high early 15th century results with centered PC calculations and 2 PCs in the AD1400 North American network and both of us get low early 15th century results with centered PC calculations and 5 PCs in the North American network.

We have tried to canvass these matters in an evenhanded way in our E&E article (see pages 75-76) to show what is agreed and what is not agreed. Mann has categorically denied that his PC method generates hockey stick shaped series from red noise (realclimate#Temperature question #5, but we see no way that he will able to sustain this argument, in the face of the compelling evidence to the contrary in our GRL paper.

Mann and ourselves agree that centered PC calculations are “standard” (for this acknowledgement see realclimate#Yet paragraph 3). We had thought that both Mann and ourselves agreed that a valid reconstruction should pass a range of statistical verification tests – this is a position which we endorse and a position which Mann seems to endorse ( see realclimate#Myth 1 3rd paragraph) .

However, it seems that Mann et al. are inconsistent on this matter and are now arguing that you should only look at one verification test (the RE statistic) to establish significance. We doubt others would endorse this position, but in any case we show in the GRL paper that their reconstruction is not statistically significant, when RE benchmarks are correctly calculated.

Both Mann and ourselves have done calculations showing that the MBH98 reconstruction is not robust to the presence or absence of bristlecone pines: this is not under dispute. We presume that Mann has done calculations showing that the MBH98 reconstruction is affected by their editing of the Gasp” tree ring series or else they wouldn’t have done the editing. Strangely, the Gasp” series is used twice in the MBH98 model: it appears simultaneously in the North American (“NOAMER”) network and in the “northern treeline” network. But only in the second usage is it edited, whereas in the NOAMER network the archived version was used.

Are you saying the 15th century was warmer than the present?

No, we are saying that the hockey stick graph used by IPCC provides no statistically significant information about how the current climate compares to that of the 15th century (and earlier). And notwithstanding that, to the extent readers consider the results informative, if a correct PC method and the unedited version of the Gasp” series are used, the graph used by the IPCC to measure the average temperature of the Northern Hemisphere shows values in the 15th century exceed those at the end of the 20th century.

Does your work disprove global warming?

We have not made such a claim. There is considerable evidence that in many locations the late 20th century was generally warmer than the mid-19th century. However, there is also considerable evidence that in parts of the Northern Hemisphere, the mid-19th century was exceptionally cold. We think that a more interesting issue is whether the late 20th century was warmer than periods of similar length in the 11th century. We ourselves do not opine on this matter, other than to say that the MBH results relied upon so heavily by the Intergovernmental Panel on Climate Change in its 2001 report are invalid.

Where can we get further information on principal components methodology?

In all our discussions, a principal component series is weighted combination of up to 70 individual tree ring series. Some readers may find it helpful to think of the Dow-Jones Index, which is a weighted average of individual stock prices. Principal component series can include negative weights, which result in showing a contrast between different series – picture a series with positive weights for finance stocks and negative weights for tech stocks.

In principal components discussions, the weights have forbidding names like eigenvectors or empirical orthogonal functions, but, at the end of the day, these are just weights. The decomposition is prescribed by the matrix algebra. There are canned programs in high level languages so that the principal components decomposition of a matrix X of time series can be obtained in one line. As we discuss in our articles, these decompositions can be highly sensitive to transformations of the data – even if the transformation only seems to be a “standardization”.

For a slightly more technical exposition see [to be inserted].

Who paid for your research?

We have neither sought nor received funding for this work. For McKitrick, undertaking the project has required considerable time away from his own economics research. For McIntyre, undertaking this project has required an unpaid leave of absence from his career in mineral exploration financing, at the cost of over a year’s foregone earnings so far.

Do you have any financial interests

We have neither sought nor received funding for this work. For McKitrick, undertaking the project has required considerable time away from his own economics research. For McIntyre, undertaking this project has required an unpaid leave of absence from his career in mineral exploration financing, at the cost of over a year’s foregone earnings so far.

Update 2007
Do you have any competing financial interests that, through their potential influence on behavior or content or from perception of such potential influences, could undermine the objectivity, integrity or perceived value of a publication (including postings at this blog)?

The above statement is taken from Nature here, which states:

Competing financial interests are defined as those that, through their potential influence on behavior or content or from perception of such potential influences, could undermine the objectivity, integrity or perceived value of a publication. They may include any of the following:

Funding: Support for a research program (including salaries, equipment, supplies, reimbursement for attending symposia, and other expenses) by organizations that may gain or lose financially through publication of this paper.

Employment: Recent (i.e. while engaged in this research project), present or anticipated employment by any organization that may gain or lose financially through publication of this paper.

Personal financial interests: stocks or shares in companies that may gain or lose financially through publication; consultation fees or other forms of remuneration from organizations that may gain or lose financially; patents or patent applications whose value may be affected by publication.

The answer is that I do not.


  1. A. Vourlas
    Posted Dec 20, 2009 at 8:08 PM | Permalink | Reply

    I’m sorry to sound like a neophyte but would you please explain the significance of using a mean for temperature data from 1961 to 1990?

  2. Miroslav Pavlicek
    Posted Feb 17, 2010 at 4:07 PM | Permalink | Reply

    While arguing with Carbonari I like tease them with the claim that power of clouds decking or power of clouds radiation forcing are easily measurable by satellites, whereas power of CO2 radiation forcing is out of measurable range. I base my claim usually on Dr. Spencer who measures cloud effects while he uses only estimation of CO2 effects as he cannot positively detect it. They tell me my arguments are refuted with this paper:


    Could any expert clarify me whether I am right or not?

  3. Bill Hirt
    Posted Mar 20, 2010 at 6:30 PM | Permalink | Reply

    Climate Audit.com

    As a new visitor to the Climate Audit blog I’ve been impressed with the critiques of various temperature measurements and the adjustments involved in assessing the “truth” about global warming, past and future. However, I haven’t noticed any discussion of the problems with the purported link between anthropogenic green house gas (AGHG) emissions and global warming. I have therefore respectfully submitted the following for your consideration. My apologies if this is old stuff!

    An August 2007 Scientific America article, “The Physical Science behind Climate Change” discusses this issue. It claims to be “The Undeniable Case for Global Warming” from AGHG emissions. I found the arguments far from “Scientific” and “Undeniable”.

    The SA article conclusions were based on computer model simulations of global temperatures with and without “forcing effects” from AGHA. They noted significant differences between the w/o AGHG (“natural forcing”) model predictions and their measured global temperatures dating back to 1980. They attributed these differences to the lack of AGHG effects in the natural forcing model. The 2007 IPCC report, based on a similar analysis, included the following in their summary report “Observed patterns of warming and their changes are simulated only by models that include anthropogenic forcings”.

    The differences between the “natural forcing” model predictions and measured global temperatures were used to determine AGHG forcing functions for their final climate prediction model. Their analysis resulted in AGHG “forcing” effects on global temperatures 10 times that from variations in the sun’s solar activity. The resulting computer simulation is the basis for predicting the catastrophic effects of increasing AGHG on global warming.

    This relative insensitivity to solar activity was refuted by a Danish National Space Center report by Henrik Svensmark and Eigil Friis-Christensen “The persistent role of the Sun in climate forcing”. It concludes with the following, “The Sun still appears to be the main forcing agent in global climate change”. Increasing the forcing effect of solar variations in the computer model reduces the temperature discrepancies and the need to assign any significant effect to AGHG. The resulting model would therefore minimize the effect AGHG emissions on future global temperatures and the need to limit these emissions.

    Bill Hirt

  4. barry
    Posted Apr 19, 2012 at 3:41 AM | Permalink | Reply

    There’s a bit of contention at WUWT that the source code for MBH98 was eventually released.

    This post of yours was pointed to as being the final word on the matter – https://climateaudit.org/2005/08/02/mbh98-source-code-status-report/ (but that’s 7 years ago…)

    Steve M, can you confirm if the original code was released, and where it may be accessed? Is there a more recent update post here that addresses the issue of accessibility?



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