A. W. Montford: The Hockey Stick Illusion

If you’ve found this review you probably know the story but basically it is this. Temperatures before the middle of the 19^th century can only be estimated indirectly from proxies: physically measurable characteristics of plants or animals which lived at earlier times and which respond to temperature changes. In 1999 a young climate researcher, Michael Mann, and colleagues published a paper in Nature which suggested that temperatures at the end of the 20^th century were higher than at any time in the previous 600 years. The graph of this, shaped like an ice-hockey stick, became iconic and appeared several times in the IPCC 2001 technical assessment report and elsewhere. In 2002 a retired mining engineer, Steve McIntyre, became suspicious of the fact that the paper both contradicted conventional wisdom and gave an ideal message for climate change activists that he started to investigate. His findings led to Congress setting up to two high level technical enquiries and a congressional committee held hearings.

Those of you who have seen my review of ‘Dire Predictions’ by Mann and Kump might imagine that I would automatically give a favourable review to this book. After all it is the very antithesis of the view of climate by IPCC insiders like Mann and Kump. But that is not how we work at climatedata.info. We try, as far as possible, to avoid polemics for polemics sake and let the data speak for themselves.

The author of this book, Andrew Montford, is a blogger who uses the pseudonym ‘Bishop Hill’. He started off as a political blogger and has a Bill of Rights for the UK on his site.  The Bill of Rights shows that he is of a libertarian disposition and is therefore not predisposed to accept the restrictions which would be necessary to bring about a major reduction in carbon emissions. He admits in the book that his site only took off when he started blogging on climate the ‘Hockey Stick’.

The book reads well, is well referenced, and appears to be a crushing indictment of the IPCC and the paleoclimatologists who developed the ‘Hockey Stick’. To the author, Steve McIntyre is definitely one of the ‘good guys’ and beyond reproach. Whilst it tries to present arguments from both sides there is no doubt that the book is very partisan.

In referring to the meeting to discuss the ‘Hockey Stick’ by the National Academy of Sciences in the USA he discusses the response of Michel Mann to a question concerning verification of the calculations. In a published paper Mann had reported that he had calculated a particular statistic (r squared). In the book he is quoted as telling the meeting “We didn’t calculate it. That would be silly and incorrect reasoning.” I have Googled those phrases and the only source I can find is Steve McIntyre’s blog at climateaudit.org which is the source referenced by the author. There appears to be no transcript of the NAS meeting, at least I could not find one online. I have also studied the transcript, and listened to much of the recording, of the subsequent congressional hearing and can find no evidence to support what is claimed to have been said at the NAS meeting. My attempts to get to the bottom of this do not prove or disprove what has been claimed but to make such a serious charge without independent  verification is a clear example of bias.

Throughout the book frequent reference is made to scientists withholding data and there is always the assumption that if data is withheld there are nefarious reasons for it. One of McIntyre’s complaints was that Bristlecone Pine trees were central to calculation of the ‘hockey stick’ but that the data from the trees stopped in 1980, just as the main warming started. He therefore set about visiting the site to resample the trees. This was done and the cores were re-analysed. I have tried to access the data using the links on his site including http://climateaudit.org/data/colorado/SMCD.dat but the links are dead. In a footnote in the book the author says [McIntyre] “has yet to publish the findings in a journal.” I am not assuming there is anything sinister in this but the fact that the author so glibly accepts the lack of openness from McIntyre but assumes ill-intent from others is a further demonstration of his bias.

Enough of the polemics: where does this leave the science?

Climate scientists are under pressure from politicians to present a clear picture. There is no dispute about the fact that many climate scientists felt that if temperatures had been warmer in the historic past than the present this would dilute the message they could deliver to the politicians. When a climate scientist appeared to be able to prove that current temperatures were indeed higher than in the past millennium they jumped at it as way of getting their message across. The ‘Hockey Stick’ became the star of the 2001 IPCC report.  However my feeling is that on balance the climate science community regrets the prominence given to the hockey stick. There are two reasons for this.

Firstly the aim of the IPCC is to convince the public of the necessity to take action on climate change. The use of temperature proxies has been so well discussed that many well informed citizens are aware of the need to ‘hide the decline’ or believe that everything is based on a few trees in Siberia. The ‘decline’ refers to the fact that in recent decades trees in  the northern hemisphere are not responding to temperature increases in the way they were assumed to; this brings into question the accuracy of long-term temperature estimate based on tree rings. Many people also believe that scientists have ‘cherry-picked’ the trees, the Yamal series from Siberia, that give the answer they want.  This was one of McIntyre’s first criticisms of Mann, that his method selected proxies that gave a ‘hockey stick’. Many scientists now would agree that temperatures in the medieval period were similar today but the science is not accurate enough to be able to say whether they were slightly warmer or cooler.

In an attempt to support the ‘hockey stick’ some climate scientists, including Mann and Kump in their book, say they accept that in parts of the world the medieval period was warm but the warming was less general than today. This argument is a bit disingenuous. In those parts of the world where written records of the medieval period exist there is evidence that medieval temperatures were high but of course not all parts of the world have written records of that period. So the argument comes down this; one side says “warming only occurred in parts of the world with written records”, and implies it did not elsewhere and the other side says “warming occurred in all parts of the world with written records” and implies that it did elsewhere.

Secondly, the question of past temperatures does not of itself determine whether or not anthropogenic warming is taking place. The temperature could be rising as a result of human action now even if temperature in the past were higher than today. Where it is critical is in discussing the impacts. If temperatures had been 2 °C higher in the past it is difficult to argue that a rise of that order of magnitude would be catastrophic.

From reading his blog I have always felt that Steve McIntyre viewed his role as scientific and he has made many attempts to reach out to the scientific community. Andrew Montford definitely has a political agenda and would probably be sceptical about climate change whatever the science said. I am not sure that McIntyre is well served by this book.

Author: A. W. Montford

Publisher: Stacy International, 2010

ISBN: 978 1 906768 35 5

Michael Mann and Lee Kump: Dire Predictions – Understanding Global Warming

The Reader’s Digest magazine used to publish what they referred to as “unexpurgated abridgements.” By this they meant that they had left in the exiting bits and cut out the boring bits. This book could be considered an “unexpurgated abridgement” of the IPCC 2004 Technical Assessment Report. A lot of the detailed science has been left out but the elevated temperatures and other symptoms associated with an attack of ‘dire era’ are given lurid prominence.

The book does give a clear and approachable synopsis of how our climate operates and how human activity can lead to changes. As an introduction to the science, the book is quite good. It is clearly written and has good supporting material. It also tackles some of the issues raised by sceptics.

In a recent double interview in Discover magazine with Judith Curry and Michael Mann, Judith Curry drew a nice distinction between ‘political sceptics’, who do not want climate change to be true, and ‘scientific sceptics’, whose opinions are based on the evidence. I would suggest that there is a third type of sceptic: the ‘bar-room’ sceptic, who’s not reticent about sharing his knowledge over the internet. You know the type “Why does the IPCC ignore the book ‘The incredible lightness of being’ by the Russian Milan Kovich which proves CATEGORICALLY that the recent so-called warming has all been due to fluctuations in the earth’s orbit?”  Unfortunately the authors tend to engage with this level of sceptic rather than the scientific sceptics. The issues where there is real scientific debate, the ‘hockey-stick’ and the urban heat island effect are either ignored or glossed over. Instead they rebut claims that the increase in CO2 is due to natural fluctuations, which scientific sceptics generally accept, or raise the hoary chestnut of “In the 70s the scientists said we were in for global cooling so why should we believe them now?”

The way they tackle the cooling/warming issue says a lot about the authors’ scientific credibility. They present a pair of graphs (page 45 in my edition) which show that the northern hemisphere temperature fell from 1940 to 1970, which explained the then current belief in cooling, and then again increased. Like the rest of their graphs there is no reference to the source but as it starts in 1850, and only the CRU record started in that year, it is reasonable to assume that that was the source.  Yet their graph is very different to the CRU one: they show temperatures rising from 1970 to the present by 1.8 °C but the CRU data shows a rise of less than half of that. Elsewhere (pages 20 and 88 in my edition) they show graphs of ‘past observed surface temperature changes’ with an almost constant rate of temperature rise and no sign of the 1940 to 1970 fall. This is very different to the above graph. Since the observed global temperature record shows similar variation to the northern hemisphere record that does not explain the anomaly. Once again without references it is difficult to be definitive but it is almost certainly the ‘modelled’ temperature increase which they have presented as ‘observed’. This gives the false impression that the temperature increases projected by the models follow on naturally from steadily rising observed temperatures.

The book is in fact heavy on dire predictions, based on model projections, but very light on evidence that the models were able to represent past changes accurately. For example, they talk of precipitation changes as being probably of ‘more importance than temperature changes’ but present not a shred of evidence of how well models simulated precipitation.  At least the IPCC report does have a shred of evidence: a graph which occupies 1/8 of a page!

What is most frustrating is the fact that this biased, one-sided, presentation of the facts is counter-productive. I fully accept that people are in part responsible for the recent temperature increase. I fully accept that there are many reasons, one of which is CO2 emissions, for reducing fossil fuel consumption. I fully accept that climate projections should play a major role in how we plan for the future. Yet, largely because the IPCC and scientists chose to ignore Abraham Lincoln’s dictum and think that in this ‘information age’ they can ‘fool all of the people all of the time’, the number of climate change sceptics is currently growing.

To give a final example: in his book “Cool It” Bjorn Lomborg mentions the 35,000 people killed in a heat wave in Europe. He also mentions that many more people die of cold in winter and follows it with a nuanced discussion of age profiles and the difficult moral question of how you balance the deaths of old people and of children. In this book only the heat deaths are mentioned. If you are an intelligent, thoughtful, person which approach is most likely to help form your opinion?

I also noticed a typo on the back cover where the book is described as being a scientifically ‘based’ overview. And where, you might ask, is the typo? It’s the missing “i” of course? 

Authors: Michael Mann and Lee Kump
Publisher: Dorling Kindersley, 2008
ISBN: 978-0-7566-3995-2

Archer and Rahmstorf: The Climate Crisis - An introductory guide to climate change

“I feel that it is important to not let bad, politically motivated science stand unchallenged.“ This is a quote we could all agree with and is part of the motivation behind our site. Only too often both ‘deniers’ and ‘warmists’ select a sub-set of the available science and then push it beyond reasonable limits to further their cause. Our mission is to sort out the justifiable from the bogus.

The authors of this book are, to use the current term, ‘warmists’. Their book is based largely on the IPCC 2007 assessment report which both of them contributed to. To their credit the authors have managed to avoid some of the recent brick-bats thrown at the IPCC. They do not repeat the scientifically dubious claims regarding Himalayan glaciers, African agriculture or the Amazonian rain forest. What is more they found no space in their book for any reference to Dr Pachauri, Chairman of the IPCC, whose commercialisation of the IPCC in the interest of organisations he is associated with has attracted much opprobrium. That said, there is a lot of politically motivated science in their book.

One of the most egregious examples of trying to gull the gullible is in their figure 3.1, reproduced below:

This purports to show that the linear trend of temperature increase is accelerating but is completely spurious for two reasons. Firstly, given that temperatures have been both rising and falling, there will always be short periods when the rate of rise is higher than the long-term average. Secondly, the 25-year rate of rise around the period 1910 to 1945 is almost the same as the 25-year period they show at the end of the record. The authors repeat their claim in the chapter summary: “Measurements unequivocally show that we are in are in the midst of an accelerating global warming”. They are wrong: there is no evidence that the rate of temperature increase is accelerating. [Postscript. The authors attribute this figure to the IPCC TAR4 Summary for Policy Makers figure 3, which does have a plot of temperatures, and I assumed they had added the rate of temperature rise. In fact the figure comes directly from the IPCC Technical Summary figure 6. So, I apologise to the authors for trying to hoodwink the public; they themselves had been hoodwinked by the IPCC.]

The authors do something similar with sea level rise. They state (correctly) that the rate of rise over the 20th century estimated from tide gauges averaged 1.7 mm/year. They also state that, in 2003 when the IPCC report was prepared, satellites had been showing a rate of increase since 1993 of 3.4 mm/year (also correct). They conclude that this indicates ‘the sea level rise has accelerated in recent decades.’ What they do not tell us, though Rahmstorf as a Professor of the Physics of the Oceans must have known, is that the rate of level rise has fluctuated and a rate of 3.4 mm/year was not unknown in the past. What they also should also have known, since their book was published in 2010, is that for the last few years the rate of rise estimated by the satellites has hovered around the long term rate of 1.7 mm/year. Again the facts show their science is politically motivated.

The book is well produced with colour photos and graphs. The use of colour seems sometimes to be at the expense of the science. The statement “in many parts of the world, the fraction of the total annual rainfall that comes down on just a few very wet ways has increased” refers to figure 3.6. Rather than a graph supporting this assertion we get a photo of bus driving through about 20 cm of water. Another example of a disconnect between the text and the cited figure relates to tropical cyclones. They quote the IPCC report as saying there is “no trend in the total number [of tropical cyclones] that occur each year” then show a graph of Tropical Cyclone counts. This graph incidentally has 4 lines, only 3 of which are referenced in the key. In relation to hurricanes the other claim they make, that ‘trends since the 1970s [are] towards more intense and longer-lasting cyclones’, may be true but ignores the fact the estimates of cyclone energy since 1851 show periods of rising energy, 1860 to 1890 and 1920 to 1950, similar to that from 1970 to 2005. The Energy Index for 2009 was actually below the average in the 1970s. The authors could not, of course have known that particular fact at the time of writing, but quoting short-term trends as evidence of long-term climate change carries the risk that a reversal of the short-term trend appears to invalidate the argument. I use the word “appears” advisably; in reality short-term trends in a system with as many “random jitters” (their phrase) as our climate say next to nothing either away about long-term changes.

One might expect the author of the quote at the head of my review to applaud my efforts to debunk politically motivated science. It won’t happen. The quote is from an email sent by Stefan Rahmstorf himself.

Authors: David Archer and Stefan Rahmstorf
Cambridge University Press, 2010
ISBN: 978-0-521-73255-0