From	Eystein Jansen	Date	Wed, 13 Sep 2006 23:21:13 +0200
To	Jonathan T. Overpeck, David Rind
CC	Keith Briffa, Stefan Rahmstorf, Bette Otto-Bleisner, cddhr@giss.nasa.gov, Fortunat Joos, Eystein Jansen, Ricardo Villalba, Tim Osborn
Subject	Re:
Hi all, My take on this is similar to what Peck wrote. My suggestion is to write: Greater uncertainty associated with proxy-based temperature estimates for individual years means that it is more difficult to gauge the significance, or precedence, of the extreme warm individual years observed in the recent instrumental record, such as 1998 and 2005, in the context of the last millennium. I think this is scientifically correct, and in essence means that we, as did the NAS panel say, feel the TAR statement was not what we would have said. I sympatise with those who say that it is not likely that any individual years were warmer, as Stefan has stated, but I don´t think we have enough data to qualify this on the hemispheric mean. Best wishes, Eystein If this is interpreted as a critisim of the TAR, then I think we At 14:09 -0600 13-09-06, Jonathan Overpeck wrote: thanks David - lets see what others think. I agree, that we don't want to be seen as being too clever or defensive. Note however, that all the TAR said was "likely" the warmest in the last 1000 years. Our chapter and figs (including 6.10) make it clear that it is unlikely any multi-decadal period was as warm as the last 50 years. But, that said, I do feel your are right that our team would not have said what the TAR said about 1998, and thus, we should delete that second sentence. any other thoughts team? thx, peck Leaving aside for the moment the resolution issue, the statement should at least be consistent with our figures. Fig. 6-10 looks like there were years around 1000 AD that could have been just as warm - if one wants to make this statement, one needs to expand the vertical scale in Fig. 6-10 to show that the current warm period is 'warmer'. Now getting back to the resolution issue: given what we know about the ability to reconstruct global or NH temperatures in the past - could we really in good conscience say we have the precision from tree rings and the very sparse other data to make any definitive statement of this nature (let alone accuracy)? While I appreciate the cleverness of the second sentence, the problem is everybody will recognize that we are 'being clever' - at what point does one come out looking aggressively defensive? I agree that leaving the first sentence as the only sentence suggests that one is somehow doubting the significance of the recent warm years, which is probably not something we want to do. What I would suggest is to forget about making 'one year' assessments; what Fig. 6-10 shows is that the recent warm period is highly anomalous with respect to the record of the last 1000 years. That would be what I think we can safely conclude the last 1000 years really tells us. David At 9:10 AM -0600 9/13/06, Jonathan Overpeck wrote: Keith - thanks for this and the earlier updates. Stefan is not around this week, but hopefully the others on this email can weight in. My thoughts... 1) We MUST say something about individual years (and by extension the 1998 TAR statement) - do we support it, or not, and why. 2) a paragraph would be nice, but I doubt we can do that, so.. 3) I suggest putting the first sentence that Keith provides below as the last sentence, in the last (summary) para of 6.6.1.1. To make a stand alone para seems like a bad way to end the very meaty section. 4) I think the second sentence could be more controversial - I don't think our team feels it is valid to say, as they did in TAR, that "It is also likely that, in the Northern Hemisphere,... 1998 was the warmest year" in the last 1000 years. But, it you think about it for a while, Keith has come up with a clever 2nd sentence (when you insert "Northern Hemisphere" language as I suggest below). At first, my reaction was leave it out, but it grows on you, especially if you acknowledge that many readers will want more explicit prose on the 1998 (2005) issue. Greater uncertainty associated with proxy-based temperature estimates for individual years means that it is more difficult to gauge the significance, or precedence, of the extreme warm years observed in the recent instrumental record. However, there is no new evidence to challenge the statement made in the TAR that 1998 (or the subsequent near-equivalent 2005) was likely the warmest of Northern Hemisphere year over the last 1000 years. 5) I strongly agree we can't add anything to the Exec Summary. 6) so, if no one disagrees or edits, I suggest we insert the above 2 sentences to end the last (summary) para of 6.6.1.1. Or should we make it a separate, last para - see point #3 above why I don't favor that idea as much. But, it's not a clear cut issue. Thoughts? Thanks all, Peck Eystein and Peck I have thought about this and spent some time discussing it with Tim. I have come up with the following Greater uncertainty associated with proxy-based temperature estimates for individual years means that it is more difficult to gauge the significance, or precedence, of the extreme warm years observed in the recent instrumental record. However, there is no new evidence to challenge the statement made in the TAR that 1998 (or the subsequent near-equivalent 2005) was likely the warmest in the last 1000 years. This should best go after the paragraph that concludes section 6.6.1.1 I believe we might best omit the second sentence of the suggested new paragraph - but you might consider this too subtle (or negative) then. I think the second sentence is very subtle also though - because it does not exclude the possibility that the same old evidence that challenges the veracity of the TAR statement exists now , as then! I think this could go in the text where suggested , but I think it best NOT to have a bullet about this point.We need to check exactly what was saidin the TAR . Perhaps a reference to the Academy Report could also be inserted here? Anyway, you asked for a straw-man statement for all to argue about so I suggest we send this to Stefan, David , Betty and whoever else you think. cheers Keith -- Professor Keith Briffa, Climatic Research Unit University of East Anglia Norwich, NR4 7TJ, U.K. Phone: +44-1603-593909 Fax: +44-1603-507784 http://www.cru.uea.ac.uk/cru/people/briffa/ -- Jonathan T. Overpeck Director, Institute for the Study of Planet Earth Professor, Department of Geosciences Professor, Department of Atmospheric Sciences Mail and Fedex Address: Institute for the Study of Planet Earth 715 N. Park Ave. 2nd Floor University of Arizona Tucson, AZ 85721 direct tel: +1 520 622-9065 fax: +1 520 792-8795 http://www.geo.arizona.edu/ http://www.ispe.arizona.edu/ -- /////////////////////////////////////////////////////////////////////////// /////////////////////////////////////////////////////////////////////////// -- Jonathan T. Overpeck Director, Institute for the Study of Planet Earth Professor, Department of Geosciences Professor, Department of Atmospheric Sciences Mail and Fedex Address: Institute for the Study of Planet Earth 715 N. Park Ave. 2nd Floor University of Arizona Tucson, AZ 85721 direct tel: +1 520 622-9065 fax: +1 520 792-8795 http://www.geo.arizona.edu/ http://www.ispe.arizona.edu/ -- ______________________________________________________________ Eystein Jansen Professor/Director Bjerknes Centre for Climate Research and Dep. of Earth Science, Univ. of Bergen Allégaten 55 N-5007 Bergen NORWAY e-mail: eystein.jansen@geo.uib.no Phone: +47-55-583491 - Home: +47-55-910661 Fax: +47-55-584330