Over on Climate Audit, Steve McIntyre has been making a series of posts that have been putting the final nails in the coffin for Michael Mann’s MBH98 paper. This paper was responsible for the famous hockey stick graph which is based on tree ring data from Bristlecone Pine trees. Mann’s work implies them to be excellent proxy indicators of temperature, and due to their age, a profound record of temperature. Problem is, it looks like most of the results is Mann’s paper have been thoroughly discredited by the work of McKittrick and McIntyre in 2005, plus McIntyre’s more recent work.
At 4600-4800 years old for some of the oldest trees, Bristlecone Pines (BCP) certainly have seen most if not more than all of human recorded history, so it seems logical to look to them for answers about our temperature history.
One of the graphs Steve McIntyre recently produced was this one:
About this graph he notes:
Here’s the MBH98 PC1 (bristlecones) again marking 1934. Given that bristlecone ring width are allegedly responding positively to temperature, it is notable that the notoriously hot 1934 is a down spike.
Since 1934 is generally accepted now to be the hottest year on record in 20th century it is indeed curious that 1934 in Mann’s data shows up as a down spike.
But seeing what happened with 1934, one has to wonder what do these trees really record in their tree ring growths? Is it temperature as Mann speculates? Or is it any number of other things related to plant growth in various combinations? Read the rest of this entry »
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