Monday, 20 February 2012

The Hockey Stick and the Climate Wars

This book was better than I expected. My expectation was based not on Mann’s reputation/caricature, but on his previous book “Dire Predictions” co-authored with Lee Kump which we have reviewed previously.
On this site and in blog contributions I’ve recently been trying to promote two themes. The first is that the climate science community is weakening its case by trying to ignore inconvenient facts and data; it then gets doubly blamed for the cover-up and the inconsistency between their claims and the data. The second theme is that when presenting climate science to a largely lay audience, as Mann does here, a scientist has to be more careful than in a published paper. A paper will be thoroughly scrutinised by other scientists; lay people will not know if the wool is being pulled over their eyes.

Much of the book deals with the ‘climate wars’ aspect of title and the fact that few attacks on climate scientists fail to include Mann or his ‘Hockey Stick’. In the USA the whole issue of climate is much more divisive than in the UK. In the UK the Climate change Bill, mandating a reduction of 80% in CO2 emissions by 2050, was passed with only 5 votes against. At a recent lecture the Director of the Grantham Institute for Climate Change, Sir Brian Hoskins, was very frank about the shortcoming in climate science.  None of this would be possible in the USA. And it goes a long way to explain why Mann devotes time to this topic. 

One of my complaints of his previous book was that Mann blithely ignored any criticisms of his work. In this book he tackles some of them – even if not always head on. One example was the use of the word ‘censored’. When the data used for his original millennial temperature reconstruction was released it contained a folder called ‘censored’. This was regarded by anthropogenic global warming antagonists as proof of malfeasance; in reality it is a normal statistical term used to define a data sub-set excluded to test its importance to the overall conclusion. Another area he deals with is what he refers to as the ‘divergence problem’. This is the fact from about 1960 onwards most tree rings fail to respond to global warming. In the case of his own work he simply says that his data sets ended in the 1970s and 1980s and claims that the idea of adding the observed temperature for recent years to bring the data up to date, and increasing the hockey stick appearance,  was suggested by a reviewer. Elsewhere he deals with a “high-elevation site in western United States”, without actually calling them ‘bristle cone pines’, and accepts that their growth rates could have been influenced by CO2 enhancement rather than temperature increases. This had been a criticism of his record. Another criticism of his work had been that one of the proxy records, sediments from a Lake in Finland, had not only been corrupted by upstream engineering works but had been used ‘upside down’. In one of comments on this Mann says “one of our methods didn’t assume orientation, while the other used an objective procedure for determining it”. This appears to be an admission that the orientation might not have been correct though elsewhere he says that this record did not change the overall conclusions. 

So, if other climate scientists might have understood the oblique references in the book how might the public react to the book. Well of course few of them would have picked up the allusions and would quite possibly have been unaware of the significance of some of the statements. Another objection of proxy records is that, for statistical reasons, they underestimate the variability of the parameter they are estimating. Mann recognises this and explains this is a reason for the wide error bands.  It is quite possible that increases in temperature such as those from 1910 to 1945 or 1975 to 2005 might have occurred in the past but not have registered in the proxy record. Again few members of the public reading this book would have understood the point and simply seen the ‘blade’ of hockey stick and not realised that the handle could have been as curvy as the blade. Another example of misleading the public is the graph he presents of a projection of temperature made in 1988 but he only includes data “available through 2005 in this analysis” even though later data were available at the time of writing the book and show the projection as been less accurate.

Elsewhere I have argued that there was need for a book in a popular style to combat the popular books of AGW antagonists – this is indeed such a book. What is now needed is a book which arbitrates between two sides.

Author: Michael E. Mann

Publisher: Columbia University Press, 2012

E-ISBN: 978-0-231-52638-8

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