Friday, March 30, 2012


date: Tue, 26 Sep 2000 09:54:47 -0400
subject: Re: Issue for TS and SPM
to: Joyce Penner <>


The implication of the current wording is that the "balance" has shifted,
whether the word "balance" is used or not. But I assume your criticism of
the wording is substantive rather than semantic. That is, in your opinion,
roughly equal weight has been added on both sides since the SAR, leaving
the "balance" unchanged. I disagree. Many factors contributed to the
overall judgment that "there is now stronger evidence...", and they are
summarized in the four bullets at the beginning of section E. From my
point of view, the key factors were the much-improved paleoclimatic data
analysis (e.g., Mann and Bradley) that help constrain low frequency
variability and demonstrate the unique behavior of inferred NH temperature
beginning fairly recently; and the introduction of multi-signal,
time-dependent detection and attribution methods which begin to constrain
the role of solar and volcanic forcing. Balancing these developments
against the broadening of the range of uncertainty for the indirect aerosol
effect that has occurred since SAR (and considering other developments on
both sides of the equation), leads me to the judgment that the "balance"
is now struck more firmly in the direction of detection of climate change
and its attribution to anthropogenic forcing.


Joyce Penner
<penner@umich. To:
edu> cc:
Sent by: Subject: Issue for TS and SPM

09/25/00 03:18

Dear all:

I had hoped to see a revision of the Chapt 12 "integrating" issue with
respect to detection in the face of uncertainties associated with aerosols,
but it never appeared. In going through my email, I see a still not-final
version of Ch. 12 executive summary that remains extremely positive:

There is now stronger evidence for a human influence on global climate than
at the time of the SAR.

This, I think, was the basis for making a stronger claim than that in the
SAR for anthropogenic influences.

I was extremely skeptical that we could make a stronger conclusion, since,
in my view, both data that was in favor of a stronger conclusion has been
added (e.g. the longer record of temperature increases) and data that was
in favor of a less strong conclusion (e.g. the high estimates of indirect
forcing from models coupled with the clear observational evidence of

In my view, adding evidence in favor and adding evidence that would shed
doubt on the interpretation of the evidence in favor means that the correct
formulation of the state of our knowledge is still that in the SAR:

"The balance of evidence ... for an anthropogenic influence".

I welcome your discussion (though I'm still not through with my chapter!!)

Joyce Penner, Professor Office: 2516 Space Research
Dept. of Atmospheric, Oceanic, Phone: 734-936-0519
and Space Sciences Fax: 734-764-4585
University of Michigan E-mail:
2455 Hayward
Ann Arbor, MI


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