Wednesday, April 25, 2012


cc: "Malcolm K. Hughes" <>, Crowley_Hegerl <>,,, Jan Esper <>,,,,
date: Mon, 10 Sep 2001 16:09:03 -0400
from: "Michael E. Mann" <>
subject: Re: Esper/Cook paper
to: Ed Cook <>

Thanks Ed,

This is extremely informative, and it looks pretty reasonable...Indeed, our
"LIA" is more pronounced in the Northern Hemishere extratropics, and gets
dampened out quite a bit by the lower amplitude tropical variability in our
domain. Admittedly, there is not much tropical proxy information prior to
1600 AD and fewer patterns calibrated (so, prior to then, our
reconstruction trends to prescribe that the tropical temperatures vary in
phase but at lower amplitude than the extratropics based on the information
in largely extratropical indicators).

But certainly during the "LIA" we have a good amount of both low and
high-lat information, and the decomposition into latitudinal range is very

To this end, it would be very useful to add the MBH 30-70N annual mean
reconstruction (AD 1600-present, which I just sent you, based on same 40
year lowpass). I think this would clarify the LIA issue further...

Interestingly, Tom's EBM simulation, when run with a higher prescribed
sensitivity, gives a colder LIA, but also a much colder MWP ! That throws
in yet another monkey wrench into the whole situation, since we all seem to
get about the same level of warmth for the MWP (you, Phil, us, Keith, etc.).



p.s. just received Keith's email--I agree that showing Briffa et al, Jones
et al, would be useful, but I think that the above suggestion might clarify
further because it is the same reconstruction, same proxy data, but simply
different latitudinal temperature average...
At 02:51 PM 9/10/01 -0400, Ed Cook wrote:
>Hi Mike et al.,
>Okay, here is an overlay plot of MBH vs. RCS, with RCS scaled to the
>1900-1977 period of MBH, and with 95% confidence limits. This has been done
>for the 40-yr low-pass RCS data to be consistent with the low-pass MBH
>series you sent me. The 95% confidence limits of the RCS are also scaled
>appropriately. Since correlations with both instrumental and MBH are
>O(0.95) after even 20-year smoothing because of the trend, the RCS limits
>are effectively based on the bootstrap 95% limits of the 14 chronologies.
>Assuming that the original RCS C.I.s are reasonably accurate (which I think
>they are), what is apparent (to me anyway) is that the confidence limits of
>MBH are uniformly narrower after AD 1600. Prior to that, they are
>comparable to RCS back to ca. AD 1200 where RCS C.I.s get bigger. Of course
>this is an odd comparison because the confidence limits are not derived the
>same way. However, I do think that they are somewhat informative
>nonetheless. What is also apparent is the much great amplitude of
>variability in the RCS estimates. This is consistent with the understanding
>that extratropical temperatures are more variable than tropical
>tempertures, which supports the idea that the MBH record does have more
>tropical temperature information in it. The other interesting thing about
>expressing the RCS data this way and overlaying it on MBH is the appearance
>that MBH is missing the LIA rather than the MWP, at least on
>multi-centennial timescales. This turns some of Broecker's criticism of the
>"hockey stick" on its head. I'm not sure where all this leads.
>Any comments and further suggestions are welcome as long as they come in by
>tomorrow. I am definately submitting the paper within a day or two.
>Dr. Edward R. Cook
>Doherty Senior Scholar
>Tree-Ring Laboratory
>Lamont-Doherty Earth Observatory
>Palisades, New York 10964 USA
>Phone: 845-365-8618
>Fax: 845-365-8152

Professor Michael E. Mann
Department of Environmental Sciences, Clark Hall
University of Virginia
Charlottesville, VA 22903
e-mail: Phone: (434) 924-7770 FAX: (434) 982-2137


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