It’s interesting what happens when one
opens Pandora’s Box! As I was putting together my article on the hockey stick
effect as I think it applies to the data and forecasts put together but the
Office of Budget Responsibility (OBR) I did a tiny amount of research into what
the rest of the world knew about the effect. One thing I came across a web page
that said that Mr X created the hockey stick effect in 2004 or 2005 or
something.
I stored that information for future
reference knowing that I first heard the term hockey stick effect at least in
the mid 1980s.
Well, The big hockey stick effect article
comes from, according to Wikipedia:
The
term hockey stick was coined by the climatologist Jerry Mahlman, to
describe the pattern, envisaging a graph that is relatively flat to 1900 as
forming the hockey stick's "shaft", followed by a sharp increase
corresponding to the "blade". [http://news.bbc.co.uk/1/hi/sci/tech/3569604.stm]
The reference is to a BBC web site page in
which is clearly says:
The
hockey stick was a term coined for a chart of temperature variation over the
last 1,000 years, which suggested a recent sharp rise in temperature caused by
human activities.
Well, no it isn’t: I can tell you where I
was and what I was doing when I probably learned the term hockey stick effect
but there is no book, article or web site to send you to. I can guarantee,
however, that Jerry Mahlman did NOT invent the term: not in the way stated by
the BBC anyway. Of course, if Mahlman coined the phrase pre 1985 or 1984 then
fine, I can accept that!
In fact, at the time of starting my
analysis of the OBR data expecting to find hockey stick effect evidence, I had
never knowingly heard of Mahlman and his hockey stick diagram. Incidentally,
here is the diagram Mahlman created:
Source: BBC web site supra
From the fascinating article entitled The rise and fall of the Hockey Stick
that I came across this morning, even if you don’t go and read the entire
article, take a look at this graphic:
The point of the controversy is, perhaps,
best illustrated by the following:
Until
the 1990s there were many, many references in scientific and historical
literature to a period labelled the Medieval Warm Period
(MWP) lasting from about AD 800–1300. It was followed by a much cooler period
termed the Little Ice Age. Based on both temperature reconstructions using proxy measures and
voluminous historical references it was accepted that the Medieval Warm Period
had been a period when global temperatures were a bit hotter than today’s
temperatures. Until about the mid-1990s the Medieval Warm Period was for
climate researchers an undisputed fact. The existence of the Medieval Warm
Period was accepted without question and noted in the first progress report of
the IPCC from 1990.
This hockey stick effect diagram became the
perceived wisdom once it was published, around 2005. Then two gentlemen came
along who seem to have been pure researchers: they were curious. Forget the
refusal to share data and the paranoia that followed.
… Steve
McIntyre linked up with Ross McKitrick … and … [t]ogether McIntyre and
McKitrick began to dig down into the data that Mann had used in his paper and
the statistical techniques used to create the single blended average used to
make the Hockey Stick. They immediately began to find problems.
… But
McIntyre and McKitrick found one major error, an error so big that it
invalidated the entire conclusion of the whole paper.
…
what Mann had done was blend together lots of different proxy studies of the
past climate going back 1,000 years and then produced an average of all these
studies and a single graph showing the trend. Clearly the validity of the
techniques used to blend together and average the different data from the
various different studies was absolutely critical as to the validity of the
final conclusions reached and the resulting Hockey Stick graph. This sort of
blending of data sets is a very common statistical exercise and there are very
well established techniques for undertaking such an exercise … Effectively what
Mann’s odd statistical techniques did was to select data that had any sort of
Hockey Stick shape and hugely increase its weight in the averaging process.
Using Mann’s technique it meant that any data was almost certain to produce a
spurious Hockey Stick shape.
I won’t go through the entire paper since I
am really interested in the hockey stick effect rather than reopening the
climate change debate. However, please go to the web page, linked to here
several times and note the comments on Briffa’s work and the article by Mann,
Bradley and Hughes, just referred to about simply as Mann.
Nevertheless, consider the following revised
view of climate change:
The 20th and 21st
centuries are NOT the warmest for 1,000 years and more.
Finally, I am not sure what has happened
since McIntyre and McItrick did their work and whether Nobel Laureate Al Gore
has revised his film, An Inconvenient Truth.
After all, any right thinking person must have thought the same as I did when I
saw that film: how can all of his graphs be so perfectly directed to prove
something that simply could not be proven? Now we know why!
DW
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