cc: owner-tar_ts@meto.gov.uk, tar_cla@meto.gov.uk, tar_ts@meto.gov.uk date: Tue, 26 Sep 2000 09:54:47 -0400 from: Michael_Oppenheimer@environmentaldefense.org subject: Re: Issue for TS and SPM to: Joyce Penner Joyce: 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. Michael Joyce Penner cc: tar_cla@meto.gov.uk Sent by: Subject: Issue for TS and SPM owner-tar_ts@m eto.gov.uk 09/25/00 03:18 PM 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 influences). 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 ****************************************************************************** Joyce Penner, Professor Office: 2516 Space Research Building Dept. of Atmospheric, Oceanic, Phone: 734-936-0519 and Space Sciences Fax: 734-764-4585 University of Michigan E-mail: Penner@umich.edu 2455 Hayward Ann Arbor, MI http://aoss.engin.umich.edu/Penner/ 48109-2143 *******************************************************************************