Posted by: climatewonk | March 30, 2008

Of Hockey Sticks and Bristlecone Pines

A quote from an old poem you may have learned as a child:

The time has come,” the Walrus said,
“To talk of many things:
Of shoes–and ships–and sealing-wax–
Of cabbages–and kings–
And why the sea is boiling hot–
And whether pigs have wings.”

I was lured into the fray, into the climate wars, over the hockey stick debate, and it is to that I hope to return one day in more detail. I am trying to arrange a directed reading course on the politics of climate policy in which I hope to focus on scientific uncertainty and how it affects the policy process, specifically, how uncertainty has been used by the “contrarians” to cast doubt on the concept of anthropogenic global warming. I will use paleoclimate reconstructions as a case study. So I have been building up a bibliography of readings I hope to review and a list of arguments I hope to address.

Recently, there has been a back-and-forth of sorts between Hansen’s Bulldog and C A. What is at issue is the MBH98 and MBH99 paleoclimate reconstructions and the M M critique. As I understand it, the main issues raised at C A are that Mann et al used a non-centred PCA methodology which gave pride of place in the PC stratum to BCPs, which are poor temperature proxies. This made for a faulty reconstruction that missed the MWP and LIA, two periods of climate variation that had been taken for granted prior to MBH and the use of it in the IPCC 2001 report.

Much text has been expended going over these issues, with HB reviewing centred and non-centred PCA and C A responding with its view of the flaws and misrepresentations of MBH. I am not qualified to offer a position on whether C A has it right or whether HB has it right as I am not up to speed on the statistical arguments. I hope, over the next few months, to spend some quality time reviewing the papers and arguments in closer detail and will post my musings as I do. The Hockey Stick Debate is important as an historical and theoretical example of what happens when politics and science collide. I’m surprised that this is still being debated but am glad it is in one sense as this is the area I want to focus on for my course. However, it has an unreal feel to it, as if we are back debating some historical issue that has little relevance to reality today — especially after reading this report on warming in the Western US.


Where I live is just north of the warmest bit on the map in the north-western states of North Dakota/Montana. We’re waming very rapidly and experiencing a drought on top of it.

Why are we still debating the hockey stick and BCPs?

Politics, my dear friends. Politics, and hence my directed reading course.


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