The hockey stick fiasco
Part 2: An artefact of poor mathematics
Not long after the hockey stick was published, shock
was to stagger the climate-change establishment when
two Canadians, Stephen McIntyre, an engineer and
brilliant mathematician, and Ross McKitrick, a climate
scientist, uncovered a fundamental mathematical flaw in
the computer program that was used to produce the MBH98
hockey stick.
In his original publications of the hockey stick,
Mann was supposed to have used a standard method known
as principal component analysis, or PCA, to find the
dominant features in a set of more than 70 different
climate records.
McIntyre and McKitrick obtained part of the
programme that Mann et al. had used, and they found
serious problems with it. Not only did the programme
not do conventional PCA, but it handled data
normalisation in a way that could only be described as
mistaken.
To illustrate the point, McIntyre and McKitrick
generated graphs using the Mann et al. algorithm using
random, computer-generated ‘red noise’
(i.e. random numbers) and added Mann’s graph compiled from the proxy
temperature datasets.[1]
In these eight graphs, it is not easy to see which
in Mann’s hockey stick graph and which are the
random noise graphs.
McIntyre et al. also tested the algorithm of Mann et
al. without the bristlecone-pine data, whereupon the
the Little Ice Age appeared. They also found that
Mann et al. had excluded from their calculations a
single dataset covering the later mediaeval warm
period, which had been stored in a computer file marked
“CENSORED_DATA”. McKitrick et al. ran the
Mann et al. computer model including the missing
dataset, and found that the mediaeval warm period
reappeared.[2-3]
McIntyre and McKitrick had difficulty getting their
findings published, they eventually were. And they
caused some consternation in the scientific world. For
example, Philip Muller, a physicist at Berkeley, said
that the two Canadian scientists’ work:
‘…hit me like a bombshell, and I
suspect it is having the same effect on many others.
Suddenly the hockey stick, the poster-child of the
global warming community, turns out to be an artefact
of poor mathematics.’
So, what is probably the most important piece of
evidence supporting a man-made component in global
warming turns out to by be a work of fiction.
References
1. McIntyre, S., and R. McKitrick,: Corrections to
the Mann et al. (1998) proxy database and northern
hemispheric average temperature series.
Energy Environ 2003; 14:
751–771.
2. McIntyre, S., and R. McKitrick. Hockey sticks,
principal components, and spurious significance.
Geophys Res Lett 2005; 32(3),
L03710, doi:10.1029/2004GL021750.
3. McIntyre, S., and R. McKitrick. The M&M
critique of the MBH98 Northern Hemisphere climate
index: Update and implications. Energy
Environ 2005; 16: 69–99.)
Part 1: The hockey stick and
real life | Part 2: An artefact of poor
mathematics
Last updated 8 March
2009
|
