I promise that I’ll get to Ammann’s answer. I’ve gotten sidetracked a little in documenting how Ammann’s unpublished work has been applied in the U.S. Congress. I’ll get to Mann’s letter to the House Energy and Commerce Committee in a minute. Meantime here is an interesting comment by Sir John Houghton to the testifying before the Senate Energy and Natural Resources Committee on July 21, 2005 archived at creationcare.org here. I won’t comment much here on what Houghton said. Most of you will already know my position as Houghton’s position seems to be the Hockey Team party line. One new point here is Houghton saying that Ammann and Wahl deal with the bristlecone pine issue. I sure haven’t seen anything like that in their articles. The Hockey Team can barely bring themselves to use the word “bristlecone” much less try to explain Mann’s handling of bristlecones. Rest assured that Ammann and Wahl have not explained the bristlecones.
I’ve pointed out before that Ammann and Wahl’s submission to GRL was rejected and was only taken out of the garbage can after they got the editor replaced. (Compare the silence on this to the hysteria about Soon and Baliunas at Climate Research.) It is disquieting in the extreme that a corporation, like the University Corporation for Atmospheric Research, should issue a press release announcing the submission of an article and then not announce the rejection. That would be a breach of securities laws requiring ongoing full disclosure for Canadian mining promotions, but seemingly not in climate research. It’s amazing the number of references that were immediately made to the UCAR press release to the U.S. Congress. I formally complained to Richard Anthes, President of UCAR about their handling of the Ammann press release and got a very unsatisfactory reply, but that’s another story.
Here’s Houghton’s testimony.
Senator Bingaman Question 8c
The Hockey Stick. In recent months, there have been assertions that the statistical method used to analyze global temperature data for the last several hundred years was biased towards generating the “hockey stick” shaped curve that shows sustained low and stable temperatures for hundreds of years with an extremely sharp rise in the last 100 years. Can you comment on whether the observations depicted in the hockey stick curve are, indeed, legitimate?
Senator Talent Question 6
What’s the status of the review of the Mann “hockey stick” temperature curve? I understand that studies by Stephen McIntyre and Ross McKitrick suggest that it relied on the statistically insignificant bristlecone pine. Is the IPCC taking another look at that work, which forms the basis for much of today’s climate change debate?
I have received a similar question from Senator Bingaman(Q8c) [Senator Talent (Q6)]. I provide the same reply to both questions.
This is a fast moving area of research. Very recently the assertions by McIntyre and McKitrick (2005a, b) (MM), alluded to in the question (references at end of answer), have been shown by several papers to be largely false in the context of the actual data used by Mann and co-workers. Ammann (a palaeontologist at the National Centre for Atmospheric Research) and Wahl of Alfred University have two papers, one in review and one in press, that reproduce the original results published by Mann et al in Nature in 1998 and Geophysical Research Letters, 1999 and prominently used in the IPCC Third Assessment Report. They demonstrate that the results of MM are due to MM having censored key proxy data from the original Mann et al (1998) data set, and to having made errors in their implementation of the Mann et al method. They specifically show that fifteenth century temperatures, related to the bristlecone pine issue, were not similar to twentieth century temperatures, as was suggested by MM.
Amman and Wahl issued a press release in May 2005 on this finding. Fuller details are at http://www.ucar.edu/news/releases/2005/ammann.shtml These authors state that they will make their full computer code available publicly.
A specific claim is made by MM that the "hockey stick" shape of the Mann et al reconstructions is derived from the way Mann et al normalise and centre their principal component pattern data. This has recently been tested. Rutherford et al (in press, Journal of Climate) have shown that essentially the same result as Mann et al is obtained using an entirely independent statistical method on similar data. This eliminates the step of representing regional tree-ring networks by principal components. The likely reason why Mann et al were able to successfully use their particular technique is because the structure of paleoclimate data is more complex than the temporal “red noise” tested by MM.
Other investigators have reconstructed climate over the past 1000 years using very different techniques and different selections of data. Some of these results are recent, and some were shown in Fig 2.21 of the IPCC Third Assessment Science Report, Climate Change 2001. These authors tend to find a greater magnitude of climate variability than did the Mann et al "hockey stick" results. In particular the "Little Ice age" centred around 1700 is generally cooler. Some of the more recent papers of this type show a Little Ice Age cooler by up to several tenths of a degree centigrade than any reconstruction shown in the Third Assessment Report in Fig 2.21, including that of Mann et al. However, all but one recent papers (Esper et al, 2002, Mann & Jones, 2003, Moberg et 2005, Huang, 2004, Jones & Mann, 2004, Bradley et al ,2003) find that the warmth of the late 20th century is still exceptional, as their reconstructions of the temperature level relative to the 20th century in the Medieval warm period are similar to the Mann et al results. Soon & Baliunas concluded that the late 20th century was not unusually warm but their methodology was flawed (Mann and Jones, 2003) as they equated hydrological influences with temperature influences and assumed that regional warmth corresponded to hemispheric warmth.
I am sure that the IPCC Fourth Assessment Report will fully take all these new findings into account. In the meantime, it is important to recognise that no evidence has emerged that seriously calls into question findings regarding the climate of the 20th century and the influence of human activities as described in the IPCC 2001 Report.
McIntyre, S. and R. McKitrick, 2005: The M and M critique of the MBH98 Northern Hemisphere climate index: update and implications. Energy and Environment, 16, 69-100.
McIntyre, S. and R. McKitrick, 2005: Hockey sticks, principal components, and spurious significance. Geophys. Res. Lett., 12, L03710, doi: 10.1029/2004GLO21750.
Anders Moberg et al, 2005. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature, 433, 613-617 doi:10.1038/nature03265
Bradley RS, et al,2003, Climate in Medieval time, Science 302 (5644): 404-405
Esper J, et al, 2002, Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability, Science, 295, 2250-2253.
Jones, PD & ME Mann, 2004. Climate Over Past Millennia. Reviews Of Geophysics 42 (2): Art. No. RG2002
Mann, ME and PD Jones, 2003: Global surface temperatures over the past two millennia. Geophys. Res. Lett., 15, 1820, doi:10.1029/2003GL017814, 20039:
Shaopeng Huang, 2004, Merging information from different resources for new insights into climate change in the past and future. Geophysical Research Letters,. 31, doi:10.1029/2004GL019781.
Soon W, Baliunas S, 2003: Proxy climatic and environmental changes of the past 1000 years . Climate Research 23 (2): 89-110 Jan 31 2003