Monday, December 12, 2011


From: "Michael E. Mann" <>
To: Tom Wigley <>
Subject: Re: [Fwd: VS: [Climate Sceptics] Mann & Jones on 1800 yrs proxies]
Date: Sat, 23 Aug 2003 04:04:54 -0400
Cc: Phil Jones <>, Gavin Schmidt <>, Michael Oppenheimer <>, Mike MacCracken <>, Tom Crowley <>,,, Ellen Mosley-Thompson <>,,, Keith Briffa <>, Kevin Trenberth <>, Tim Osborn <>, Gabi Hegerl <>, Stefan Rahmstorf <>,, Eric Steig <>,

Thanks Tom,
I agree--the issue is not completely settled, and thanks for the reference (any possibility
you can send me a reprint?). The point here of course is that we are talking a potential
effect, w/ as you say, at best a weak signal--hardly the dominating overprint that is
argued by the Idso brothers! (by the way, weren't they a circus act at one point??),
At 12:48 PM 8/22/2003 -0600, Tom Wigley wrote:

Thanks for your clarifications.
With regard to the CO2 fertilization effect on tree ring width, I wrote a paper a number
of years ago pointing out that there were signal-to-noise problems in identifying and
quantifying such factors.
Wigley, T.M.L., Jones, P.D. and Briffa, K.R., 1987: Detecting the effects of acidic
deposition and CO2-fertilization on tree growth. (In) Methods of Dendrochronology.
Vol. 1, Proceedings of the Task Force Meeting on Methodology of Dendrochronology:
Krak�w, Poland, 26 June 1986, (eds. L. Kairiukstis, Z. Bednarz and E. Feliksik),
International Institute for Applied Systems Analysis, Agricultural Academy of Krak�w,
Polish Academy of Science, WOSI Wsp�lna Sprawa 38/37 no. 20, 239253.
While I am confident that you are correct, and that this is not a crucial factor, I
think one should be careful about denying its existence. There are, furthermore,
additional obfuscating factors that make the effects of CO2 fertilization on ring widths
hard to identify.
Perhaps more important is the fact that many tree ring based reconstructions use density
data, and the jury is still out on whether more CO2 increases or decreases density.
Michael E. Mann wrote:

Dear Colleagues,
Several you have inquired about the below claims by the notorious "Idso brothers" which
relates to the paper by Mann and Jones that appeared in GRL a couple weeks ago.
Of course, its the usual disinformation we've come to expect from these folks, but a few
details on why:
1) The supposed "Co2 fertilization" argument is a ruse. The only evidence that such an
effect might actually play some role in tree-growth trends has been found in high
elevation sites in western North America (consult Malcolm Hughes for more details). As
in Mann et al '99 (GRL), any such effect, to the extent it might exist, has been removed
from the relevant series used in the latest (Mann and Jones) paper through the removal
of anomalous differences between low-elevation and high-elevation western North American
temperature trends during the post 1800 period, prior to use of the data in climate
2) We haven't in the past extended the proxy reconstruction beyond 1980 because many of
the proxy data drop out. However, the repeated claim by the contrarians that post-1980
proxy data don't show the warming evident in the instrumental record has finally
prompted me to go ahead and perform an additional analysis in which the
proxy-reconstruction is extended forward as recently as at all possible (to 1995, for
which 3 out of 8 of the NH records are available, and 1 of the 5 SH records are
available). The SH and GLB reconstructions are thus obviously tenuous at best, but they
do address, to the extent at all possible, the issue as to whether or not the proxy
reconstructions show the post-1980 warming--and they do.
See the attached plot which compares the NH (blue), SH (green), and GLB (red) series
through 1995. The late 20th century is the nominal maximum for all 3 series *without any
consideration of the information in the instrumental mean series*. This thus refutes
the 2nd criticism cited by the Idso brothers.
One note about the 40 year smoothing. As in the trends in the instrumental series shown
by Mann and Jones, a boundary constraint on the 40-year smooth has been used that
minimizes the 2nd derivative at the boundary--this trends to preserve the trend near the
end of the series and has been argued as the optimal constraint in the present of
nonstationary behavior near the end of a time series (Park, 1992; Ghil et al, 2002). I
favor the use of this constraint in the smoothing of records that exhibit a significant
trend as one approaches the end of the available data. This might be worth talking about
in the next IPCC when the subject of adopting uniform standards for smoothing data, etc.
are discussed...
In retrospect, Phil and I should have included this analysis in the GRL article, but its
always hard to know what specifics the contrarians are going to target in their attacks.
This analysis however, will be included in a review paper by Jones and Mann on "climate
in past millennia" that is presently being finalized for "Reviews of Geophysics".
I hope that helps clarify any questions any of you might have had. Please feel free to
pass this information along to anyone who might benefit from it.
Now, back to fighting the "Shaviv and Veizer" propaganda along w/ Ben Santer and David
Parker out in Italy...

-------- Original Message --------
Subject: VS: [Climate Sceptics] Mann & Jones on 1800 yrs proxies
Date: Wed, 20 Aug 2003 13:52:40 +0300
From: Timo H�meranta <>
To: <>
CC: "Charles F. \"Chick\" Keller" <>, "Kirill Ya.
Kondratyev" <>, "Michael C. MacCracken"
<>, "S. Fred Singer" <>, "Sallie
Baliunas" <>, "Carl Wunsch" <>,
"David R. Legates" <>, "George Kukla"
<>, "James E. Hansen" <>,
"Tom Wigley" <>, "Willie Soon" <>
Dear all,
GRL finally published the study
Mann, Michael E. and Phil D. Jones, 2003. Global surface temperatures
over the past two millennia, Geophysical Research Letters Vol. 30, No.
15, 1820, 10.1029/2003GL017814, August 14, 2003
[1] We present reconstructions of Northern and Southern Hemisphere
mean surface temperature over the past two millennia based on
high-resolution ?proxy? temperature data which retain millennial-scale
variability. These reconstructions indicate that late 20th century
warmth is unprecedented for at least roughly the past two millennia for
the Northern Hemisphere. Conclusions for the Southern Hemisphere and
global mean temperature are limited by the sparseness of available proxy
data in the Southern Hemisphere at present.
We already noticed the study in
Mann, Michael, Caspar Ammann, Kevin Trenberth, Raymond Bradley, Keith
Briffa, Philip Jones, Tim Osborn, Tom Crowley, Malcolm Hughes, Michael
Oppenheimer, Jonathan Overpeck, Scott Rutherford, and Tom Wigley, 2003.
On Past Temperatures and Anomalous Late-20th Century Warmth. Eos, Vol.
84, No. 27, page 256, July 8, 2003
There we found that " .... an extension back through the past 2000
years based on eight long reconstructions [Mann and Jones,2003]."
CO2 Science Magazine today presents the study as follows:
Was Late 20th Century Warming Really Unprecedented Over the Past Two
Mann, M.E. and Jones, P.D. 2003. Global surface temperatures over the
past two millennia. Geophysical Research Letters 30: 10.1029/2003GL017814.
What was done
Using 23 individual proxy records from 8 distinct regions in the
Northern Hemisphere and 5 proxy records from the Southern Hemisphere,
the authors constructed Northern and Southern Hemispheric and global
mean temperature histories over the period AD 200 to as close as they
could get to the present employing a 40-year lowpass filter of the data.
What was learned
Mann and Jones say their temperature reconstructions indicate that "late
20th century warmth is unprecedented for at least roughly the past two
millennia for the Northern Hemisphere." They also say their data and
analysis "suggest a similar, but less definitive conclusion, for the
global mean."
Although we and many others have many bones to pick with many aspects of
Mann and Jones' analysis, we will here focus on just a couple of points
and temporarily grant them the benefit of the doubt in those other areas.
First of all, granting them almost everything they have done, it can
readily be seen from their own graph of their own results that the end
point of their reconstructed global mean temperature history is not the
warmest period of the prior 1800 years. In fact, their treatment of the
data depicts three earlier warmer periods: one just prior to AD 700, one
just after AD 700 and one just prior to AD 1000 (see figure below).
Reconstructed global temperature anomaly (based on 1961-1990
instrumental reference period) adapted from Mann and Jones (2003).
The globe only becomes warmer in the 20th century when its measured
temperatures are substituted for its reconstructed temperatures. This
approach is clearly unacceptable; it is like comparing apples and
oranges. If one has only reconstructed temperatures from the distant
past, one can only validly compare them with reconstructed temperatures
from the recent past.
Another important point that is ignored by Mann and Jones is that the
last century witnessed a dramatic increase in atmospheric CO2
concentration, which everyone knows is an effective aerial fertilizer.
It also witnessed a dramatic increase in atmospheric nitrogen
deposition, which further enhances plant growth. Consequently, as
tree-ring data comprise the bulk of the proxy temperature information
employed by Mann and Jones, their reconstructed global mean temperature
history must possess a non-temperature-induced pseudo-warming signal
driven by CO2- and nitrogen-induced increases in growth that make 20th
century warming appear significantly greater than it really is. Hence,
there could well be still other periods of the past 1800 years (in
addition to the three we have already noted) when the global mean
temperature was also warmer than it was at the end of their
reconstructed record in the 20th century.
What it means
Mann and Jones have clearly failed to demonstrate the key point they
desired to make in their paper. Their data, however, speak for
themselves in clearly demonstrating that late 20th century warmth was
not unprecedented over the past two millennia.
We have already discussed about this study in July under title ?Empire
Strikes back on Soon et al.? �
All the best
Timo H�meranta
Moderator, Climatesceptics

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

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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