Email 4990, Mar 2006, Richard Alley to Michael Mann: "she was not convincing that trees were thermometers when it was warm a millennium ago but are not thermometers when it is warm now"

Email 4990

The triggering issue was the "divergence" problem as raised by Rosanne
D'Arrigo, that a spatially and temporally complex difference has arisen
between many of the long tree-ring records and the instrumental record more
recently than the calibration period in many cases. This has been in the
literature for a while, as you know much better than I do, and was not
highlighted by Rosanne in her talk, but some committee members jumped on it
in questions, and she was not convincing that trees were thermometers when
it was warm a millennium ago but are not thermometers when it is warm now.
...(I'm happy to go into details as to why the arguments were not convincing,
insofar as I captured the arguments, but they were not convincing to me, and
looking around the committee room, I don't think they were convincing to
important members of the committee.)
...I don't want to stir up trouble, I don't want to piss off the tree-ring people yet again,
but I do think that the tree-ring workers (and by
association, all of us who do climate change) have a serious problem, and
have not answered it very well yet. If better answers are out there, I hope
that they come out soon.