cc: t.osborn@uea.ac.uk date: Thu, 16 Feb 2006 00:19:18 +0100 from: Eystein Jansen subject: Re: Bullet debate number 1 to: Jonathan Overpeck , Keith Briffa Hi, I think we should avoid discussing the Moberg et al results in the exec. bullet. I also think we need to have a statement about the MWP in the bullet, and I cannot really understand why the most central conclusion from the very nice recent Osborn et al. Science paper cannot be highlighted in the first bullet. My suggestion is: o Some of the post-TAR studies indicate greater multi-centennial Northern Hemisphere temperature variability than was shown in the TAR, due to the particular proxies used, and the specific statistical methods of processing and/or scaling them to represent past temperatures. The additional variability implies cooler temperatures, predominantly during the 12th to 14th, the 17th, and the 19th centuries. The warmer period in the 11th century is in general agreement with the results shown in the TAR. Consideration of the regional records of temperature for the 11th century indicate that it is unlikely that the spatial extent of warming during this time period was as significant as in the second half of the 20th century. Cheers, Eystein At 11:46 -0700 15-02-06, Jonathan Overpeck wrote: Hi Keith (and Eystein - we need your opinion) - thanks for the quick response. I think it easier (imagining the mess of email that could result) if we focus on one bullet/email. So I'll start w/ the first, and hope that Eystein can also weigh in. With regard to the first one below, I agree that we can leave statistics out of it. Good point. But, I think we must at least address Susan's concern. To do otherwise would be counterproductive. She makes sense. I think your MWP results is quite appropriate - they were published in Science, and in my reading of the paper, you are convincing. If it's in the chapter, it makes sense to draw on it for the exec summary. Please defend more convincingly, or suggest an alternative way to deal with Susan's concern - what is the significance (not statistical) of this one record being warmer? We need to say it. If you really want to leave as is, please write your response in a way that I can forward to Susan - we can't ignore he comment in this case, because other (me, at least) think it makes sense. So we have to convince her too - this is big stuff for the AR4, and will be in the TS/SPM. We can't be as vague as the current bullet is. And as for the MWP box fig, I think it should be as you suggest - combine the existing fig w/ the new one from Tim and your paper. I think Tim might already be working on it? Sorry to be a tough guy, but this bullet needs to be more clear. Thanks, peck Peck do not think you will like what I say here , but I am going to give straight answers to your questions. First The new draft says enough in the text now about "far-less-accurately dated" and "low-resolution proxy records that can not be rigorously calibrated" in relation to this paper (Moberg et al.) . It is not appropriate to single the one series out for specific criticism in the summary . The use of the word "only" implies we do not believe it. Mike Mann's suggestion begs a lot of questions about what constitutes "significantly warmer". You need to have a Null Hypothesis to test . If you mean would the estimates in Moberg and the other reconstructions (during medieval time) show significantly different means using a t-test - then of course not , but this tells us nothing other than they are not likely samples from totally different populations - an almost impossible test to pass given the wide uncertainties on all reconstructions . Incidentally, we do not have formal (calibration ) uncertainties for Moberg anyway (just boot-strapped uncertainty on the average low-frequency curve). I think the vagueness is necessary - "suggests slightly" and is appropriate. I would not call out The results of Tim and my paper either. It is just an aside in the Medieval box at present , perhaps with a Figure to accompany the original if you agree, but without more text in the Chapter , which I do not consider appropriate, it should not be highlighted as a bullet. -- 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