Future prospects - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 343

out variations in the past, while use of recent unreliable terrestrial temperature
data, biased by urban heating and other aberrations, will exaggerate the tempera-
ture rise of the past century relative to the past. Indeed, their finding that global
temperature increased by 1.0 C since 1900 is considerably greater than what has
been widely reported by others. What is more, Mann et al. (2008) found them-
selves faced with a problem: their tree ring proxies did not rise in the late 20th
century when most of the temperature rise is claimed to have occurred. So, they
were crafty enough to use what Phil Jones referred to as Mann's ''trick'' in which
they did not show the proxy data late in the 20th century and, instead, put in the
alarmists' view of the rising global temperature measured in the late 20th century.
However, as Figures 11.2a and 11.3 show, global temperatures have not risen
continuously upward in the past 30 years as MBH would have you believe.
Nevertheless, the far right of their graphs for the last 30 years show a red line
zooming upward.
Recently, McShane and Wyner (2010) (M&W) reviewed the hockey stick from
the point of view of statistical analysis. They claimed that the hockey stick is a
clever piece of public relations but it does not have the valid implications that a
naive reader might suppose. The apparent agreement between the model and the
data in the period after 1850 was forced by tuning the model to the data. The
estimated implicit uncertainty in the data is optimistic but, even so, is so wide as
to encompass almost any past temperature profile.
M&W went on to say:

the task [of analyzing past proxy data to infer global average
temperature history] is highly statistical [and] extremely dicult. The data is
spatially and temporally auto-correlated. It is massively incomplete. It is not
easily or accurately modeled by simple autoregressive processes. The signal is
very weak and the number of covariates greatly outnumbers the number of
independent observations of instrumental temperature.''

'' ...

There are two points here. One is that, by implication, MBH changed the
rules of the game to achieve a desired result in an unscientific unprofessional
manner. The other is that by doing this the hockey stick shape was relegated to
the fourth level of principal component analysis, which infers low credibility.
Michael Mann, in his rebuttal testimony before Congress, continued to stubbornly
defend his turf, which is understandable since his whole scientific reputation
depended on it? He claimed that many subsequent peer-reviewed studies confirmed
his findings, but all of these studies used variants of his approach and were
peer-reviewed by the paleoclimatic cabal. In particular, they all used skew-
centering, as evidenced by the fact that the data were not spread across the zero
line roughly equally. Furthermore, as Climategate has revealed, peer review in
paleoclimatology is mainly a mutual armation by members of the club. This
was the backdrop for the study by M&W to reexamine the issues involved in
reconstructing past global climates from proxy data.
The precision of various proxies at representing temperature and only