Edward J. Wegman: critique of climatology research

2007-03-21

Richard Moore

         The controversy of the MBH98/99 methods lies in that the
         proxies are incorrectly centered on the mean of the period
         1902-1995, rather than on the whole time period. The proxy
         data exhibiting the hockey stick shape are actually
         decentered low. The updated MBH99 reconstruction is given in
         Figure 3. This fact that the proxies are centered low is
         apparent in Figure 3 because for most of the 1000 years, the
         reconstruction is below zero. Because the 'hockey stick'
         proxies are centered too low, they will exhibit a larger
         effective 'variance', allowing the method to exhibit a
         preference for selecting them as the first principal
         component.

         Figure 8 is a graphic that depicts a number of papers in the
         paleoclimate reconstruction area together with some of the
         proxies used. We note that many of the proxies are shared.
         Using the same data also suggests a lack of independence.

         The MBH98/99 work has been sufficiently politicized that
         this community can hardly reassess their public positions
         without losing credibility. Overall, our committee believes
         that the MBH99 assessment that the decade of the 1990s was
         the likely the hottest decade of the millennium and that
         1998 was likely the hottest year of the millennium cannot be
         supported by their analysis.

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Original source URL:
http://www.urban-renaissance.org/urbanren/publications/Wegman[2].pdf

Ad Hoc Committee Report on the 'Hockey Stick' Global Climate Reconstruction

Testimony of Edward J. Wegman

I would like to begin by circumscribing the substance of our report. 
We were asked to provide an independent verification by statisticians 
of the critiques of the statistical methodology found in the papers 
of Drs. Michael Mann, Raymond Bradley and Malcolm Hughes published 
respectively in Nature in 1998 and in Geophysical Research Letters in 
1999. These two papers have commonly been referred to as MBH98 and 
MBH99. The critiques have been made by Stephen McIntyre and Ross 
McKitrick published in Energy and Environment in 2003 and in Energy 
and Environment and in Geophysical Research Letters in 2005. We refer 
to these as MM03, MM05a, and MM05b respectively. We were also asked 
about the implications of our assessment. We were not asked to assess 
the reality of global warming and indeed this is not an area of our 
expertise. We do not assume any position with respect to global 
warming except to note in our report that the instrumented record of 
global average temperature has risen since 1850 according to the MBH 
99 chart by about 1.2o centigrade. In the NAS panel Report chaired by 
Dr. North, .6o centigrade is mentioned in several places.

Our panel is composed of Edward J. Wegman (George Mason University), 
David W. Scott (Rice University), and Yasmin H. Said (The Johns 
Hopkins University). This Ad Hoc Panel has worked pro bono, has 
received no compensation, and has no financial interest in the 
outcome of the report.

[Go to Figure 1]

MBH98, MBH99 use several proxy indicators to measure global climate 
change. Primarily, these include historical records, tree rings, ice 
cores, and coral reefs. More details of proxies are given in the 
report and mentioned in the written testimony. [The width and density 
of tree rings vary with climatic conditions (sunlight, precipitation, 
temperature, humidity, and carbon dioxide and nitrogen oxides 
availability), soil conditions, tree species, tree age, and stored 
carbohydrates in the trees. The width and density of tree rings are 
dependent on many confounding factors, making isolation of the 
climatic temperature signal uncertain. It is usually the case that 
width and density of tree rings are monitored in conjunction in order 
to more accurately use them as climate proxies. Ice cores are the 
accumulation of snow and ice over many years that have recrystallized 
and have trapped air bubbles from previous time periods. The 
composition of these ice cores, especially the presence of hydrogen 
and oxygen isotopes, provides a picture of the climate at the time. 
The relative concentrations of the heavier isotopes in the condensate 
indicate the temperature of condensation, allowing for ice cores to 
be used in global temperature reconstruction. In addition to the 
isotope concentration, the air bubbles trapped in the ice cores allow 
for measurement of the atmospheric concentrations of trace gases, 
including greenhouse gases carbon dioxide, methane, and nitrous 
oxide.]

[Go to Figure 2]

Some examples of tree ring proxy series are given in Figure 2. Most 
of the proxy series show little structure, but the last two show the 
characteristic 'hockey stick' shape. The principal component-like 
methodology in MBH 98/99 preferentially emphasizes these shapes as we 
shall see.

Principal component analysis methodology is at the core of the 
MBH98/99 analysis methodology. Principal component analysis is a 
statistical methodology often used for reducing datasets with many 
variables into datasets with fewer, but composite variables. The time 
series proxy data involved are transformed into their principal 
components, where the first principal component is intended to 
explain most of the variation present in the data variables. Each 
subsequent principal component explains less and less of the 
variation. In the methodology of MBH98/99, the first principal 
component is used in the temperature reconstruction.

[Go to Figure 3]

Two principal methods for temperature reconstructions have been used; 
CFR (climate field construction used in MBH98/99) and CPS 
(climate-plus-scale). The CFR is essentially the principal component 
based analysis and the CPS is a simple averaging of climate proxies. 
The controversy of the MBH98/99 methods lies in that the proxies are 
incorrectly centered on the mean of the period 1902-1995, rather than 
on the whole time period. The proxy data exhibiting the hockey stick 
shape are actually decentered low. The updated MBH99 reconstruction 
is given in Figure 3. This fact that the proxies are centered low is 
apparent in Figure 3 because for most of the 1000 years, the 
reconstruction is below zero. Because the 'hockey stick' proxies are 
centered too low, they will exhibit a larger effective 'variance', 
allowing the method to exhibit a preference for selecting them 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 on the overall mean is a critical factor in using 
the principal component methodology properly.

[Go to Figure 4]

To illustrate this, we consider the North America Tree series and 
apply the MBH98 methodology. The top panel shows the result from the 
de-centering. The bottom panel shows the result when the principal 
components are properly centered. Thus the centering does make a 
significant difference to the reconstruction.

[Go to Figure 5]

To further illustrate this, we digitized the temperature profile 
published in the IPCC 1990 report and applied both the CFR and the 
CPS methods to them. The data used here are 69 unstructured noise 
pseudo-proxy series and only one copy of the 1990 profile. The upper 
left panel illustrates the PC1 with proper centering. In other words, 
no structure is shown. The other 3 panels indicate what happens using 
principal components with an increasing amount of de-centering. 
Again, the single series begins to overwhelm the other 69 pure noise 
series. Clearly, these have a big effect.

It is not clear that Mann and associates realized the error in their 
methodology at the time of publication. Our re-creation supports the 
critique of the MBH98 methods.

In general, we found the writing in MBH98 and MBH99 to be somewhat 
obscure and incomplete and the criticisms by MM03/05a/05b to be 
valid. The reasons for setting 1902-1995 as the calibration period 
presented in the narrative of MBH98 sounds plausible, and the error 
may be easily overlooked by someone not trained in statistical 
methodology. We note that there is no evidence that Dr. Mann or any 
of the other authors in paleoclimate studies have had significant 
interactions with mainstream statisticians.

Because of this apparent isolation, we decided to attempt to 
understand the paleoclimate community by exploring the social network 
of authorships in temperature reconstruction.

[Go to Figure 6]

We found that at least 43 authors have direct ties to Dr. Mann by 
virtue of coauthored papers with him. Our findings from this analysis 
suggest that authors in the area of this relatively narrow field of 
paleoclimate studies are closely connected. Dr. Mann has an unusually 
large reach in terms of influence and in particular Drs. Jones, 
Bradley, Hughes, Briffa, Rutherford and Osborn.

[Go to Figure 7]

Because of these close connections, independent studies may not be as 
independent as they might appear on the surface. Although we have no 
direct data on the functioning of peer review within the paleoclimate 
community, but with 35 years of experience with peer review in both 
journals as well as evaluation of research proposals, peer review may 
not have been as independent as would generally be desirable.

[Go to Figure 8]

Figure 8 is a graphic that depicts a number of papers in the 
paleoclimate reconstruction area together with some of the proxies 
used. We note that many of the proxies are shared. Using the same 
data also suggests a lack of independence.

The MBH98/99 work has been sufficiently politicized that this 
community can hardly reassess their public positions without losing 
credibility. Overall, our committee believes that the MBH99 
assessment that the decade of the 1990s was the likely the hottest 
decade of the millennium and that 1998 was likely the hottest year of 
the millennium cannot be supported by their analysis. Recommendations

Recommendation 1. Especially when massive amounts of public monies 
and human lives are at stake, academic work should have a more 
intense level of scrutiny and review. It is especially the case that 
authors of policy-related documents like the IPCC report, Climate 
Change 2001: The Scientific Basis, should not be the same people as 
those that constructed the academic papers.

Recommendation 2. We believe that federally funded research agencies 
should develop a more comprehensive and concise policy on disclosure. 
All of us writing this report have been federally funded. Our 
experience with funding agencies has been that they do not in general 
articulate clear guidelines to the investigators as to what must be 
disclosed. Federally funded work including code should be made 
available to other researchers upon reasonable request, especially if 
the intellectual property has no commercial value. Some consideration 
should be granted to data collectors to have exclusive use of their 
data for one or two years, prior to publication. But data collected 
under federal support should be made publicly available.

Recommendation 3. With clinical trials for drugs and devices to be 
approved for human use by the FDA, review and consultation with 
statisticians is expected. Indeed, it is standard practice to include 
statisticians in the application-for-approval process. We judge this 
to be a good policy when public health and also when substantial 
amounts of monies are involved, for example, when there are major 
policy decisions to be made based on statistical assessments. In such 
cases, evaluation by statisticians should be standard practice. This 
evaluation phase should be a mandatory part of all grant applications 
and funded accordingly.

Recommendation 4. Emphasis should be placed on the Federal funding of 
research related to fundamental understanding of the mechanisms of 
climate change. Funding should focus on interdisciplinary teams and 
avoid narrowly focused discipline research.

[figures and graphs in PDF original]
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