Thursday, December 29, 2011


From: Kevin Trenberth <>
To: Michael Mann <>
Subject: Re: ENSO blamed over warming - paper in JGR
Date: Wed, 29 Jul 2009 10:23:09 -0600
Cc: Grant Foster <>,, "J. Salinger" <>,,, Gavin Schmidt <>, James Annan <>

Hi all
Wow this is a nice analysis by Grant et al. What we should do is turn this into a learning
experience for everyone: there is often misuse of filtering. Obviously the editor and
reviewers need to to also be taken to task here. I agree with Mike Mann that a couple of
other key points deserve to be made wrt this paper. Making sure that the important
relationships and role of ENSO on interannual variability of global temperatures should
also be pointed out with some select references (as in recent emails and the refs
therein). In terms of the paper, I recommend consolidating the figures to keep them fewer
in number if this is a comment: combine Figs 3 with 4 , and 6 with 7. Make sure the plots
of spectra have period prominently displayed as well as frequency and maybe even highlight
with stipple some bands like >10 years. Glad to sign on: I would need an acknowledgment
that NCAR is sponsored by NSF.
Michael Mann wrote:

thanks Grant, the paper is starting to shape up well now. Jim and I (well, mostly Jim,
w/ some input from me) are iterating on a blurb about past studies on ENSO/temperature
relationships and should have something for you soon on that,

As James has pointed out, its important to stick to the key points and not get sidetracked
with nonsense. I would avoid any commentary on their ignorant ramblings about the Hadley
Cell, etc. We want to cut straight to the deep flaws in their analysis which are, in order
of importance in my view,

1. indefensible use of a differencing filter, which has the effect of selectively damping
low-frequency variability and renders any conclusions about factors underlying long-term
trends completely spurious.

2. ignoring the fact that the influence of ENSO on global temperature has been known for
decades, and much better quantified in past studies than in the current deeply flawed

3. the selective use of a flawed temperature data and curious splicing in of inappropriate
recent data (UAH TMT) to further suppress trends. A bit of overkill given that they
already eliminated the trends anyway. Guess they wanted to play it extra cautious just in
case some bit of warming trend tried to sneak in.

The other stuff is just a distraction.


On Jul 29, 2009, at 10:51 AM, Grant Foster wrote:

Attached is a zip file with LaTeX and pdf for a first draft. I've included everybody's
name (in alphabetical order after mine), but of course it should only include in submission
those who give explicit consent.
There are a few other issues. One is that MFC have recently removed the pdf version of
their paper from the "New Zealand Climate Coalition" website. They've replaced it with
which refers to a graph showing only part of figure 7, and suggests that there's not trend
in GTTA so "nothing to worry about." Yet the plotted GTTA is from UAH TMT (*not* TLT) so
of course it shows no trend, and the MT channel is contaminated by stratospheric cooling.
In figure 7 of the paper itself they compare the 50-year record of SOI and GTTA, but their
graph of GTTA is made of RATPAC-A data until 1980 grafted onto UAH TMT data afterward --
hence the lack of an obvious trend. I think this too should be mentioned, especially as
the entire RATPAC-A record shows a very pronounced trend.
One last thing: there's a lot of stuff in the paper about Hadley cells and heat transport
and so forth. I suspect this is really a bunch of gobbledygook -- but I don't know. But
I'll bet you guys do. Comments?

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Michael E. Mann
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website: [4]
"Dire Predictions" book site:

Kevin E. Trenberth e-mail: [6]
Climate Analysis Section, [7]
P. O. Box 3000, (303) 497 1318
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