date: Wed, 4 May 2005 11:15:32 -0700 from: Jonathan Overpeck subject: [Wg1-ar4-ch06] Comments from David Rind to: wg1-ar4-ch06@joss.ucar.edu Hi Chap 6 Colleagues - Eystein will be sending out a email from him and me tomorrow, so please look for it - it gives an overview of what you should be prepared to do at the meeting, and what preparation before the meeting should be completed. We're assuming you have already read all the comments that have been sent (both from official reviewers and from each other). You should have all of these. Eystein will also send a logistics email about Monday. I've sent him my input for these two emails this morning. It turns out that David Rind won't be able to join us in Beijing for some US bizarre government rules. I'm leaving his email intact so you can read about the frustrating catch-22 he is in. It also reveals how the US government is working - not the democracy we grew up with. MORE IMPORTANTLY, David has provided some sage input for our discussions in Beijing. PLEASE READ and think about the issues he raises. Dominique and Jean Claude will both be unable to join us for health reasons. I join you all in hoping that they get better soon. If they are able to send any comments for us to consider, they will. Please keep an eye out for Eystein's email tomorrow, and in the meantime, make sure you've read all the comments, and that you BRING them ALL to the meeting. Thanks, Peck X-Sieve: CMU Sieve 2.2 Date: Wed, 27 Apr 2005 15:02:45 -0400 To: Jonathan Overpeck , Eystein Jansen From: David Rind Subject: Re: [Wg1-ar4-ch06] Review comments Hi Jonathan and Eystein, First a quick word about my situation (or lack thereof), and then some comments about the reviews. Apparently the typhoid vaccine will finally become available in the near future, perhaps as early as later this week. However, it's a moot point - NASA requires a 2 month lead time for international travel, so the timing is fine for a China meeting in August (which Ron Miller here at GISS will now be able to go to), but not for anything before July. If there was any flexibility here (and Jim Hansen was not allowed to go to India with a 2 week lead-time) it would not apply to me, because I don't yet have a 'government' passport. I could not get the government passport ahead of time because it is only issued in conjunction with approved international travel, which starts with the medical clearance. Nobody will say so directly, but I bet the reason it wasn't available (and as I was told, many travelers were 'inconvenienced'), was that the government was stockpiling it in case of a terrorist attack on the water supply. [It truly wasn't available - not here in NY, nor in several other cities along the east coast where I had friends call up and ask - as the people at the Cornell Medical Center told me it wouldn't be. The fact that they were so sure implied to me they knew what was going on.] Anyway - I'll do what I can in conjunction with whatever comes out of the meeting - and I've already sent you my opinions about the document as it stands, as well as the overlap with chapters 2 (primarily the solar forcing), and chapter 9. I looked at chapter 10 (the other chapter I'm the liaison for), and there are just a few points of overlap which could be discussed some other time. As far as the reviews are concerned: 1)The suggestion about reorganizing the chapter should be considered seriously - there are many points over overlap, and some inconsistently from one section to another - but I don't know that one suggested format (to go by historical time period) is proper either. For one thing, it is boring, and it will also lead many readers to just ignore sections prior to the last 1000 years (as NOAA apparently is already doing!). The ability to understand and model more extreme climates is an important part of why the paleochapter is here - if climate warms by 4°C in the next 100 years, looking at the climate, the consequences, and modeling capability for climate changes of 0.5°C does not help very much. I've already laid out what I think the inconsistencies are, and we could work to merge sections that really have repetition, but I think it is important to evaluate models over the suite of time-scales, forcings and magnitudes of response that paleoclimate situations offer. Having it together I think gives readers a sense of what models can and cannot do, and the uncertainties. If these are all relegated to their individual time-slices, I think you lose that perspective. I also like having the Synthesis and Implications for Climate change combine ideas from the different time periods - it gives paleoclimate studies more of an unified feel, as if it were a real discipline rather than a bunch of people doing their own time-period thing. That's necessary for IPCC, and necessary for the outside community to see as well. So I would vote for keeping the general order, but eliminating the overlap and inconsistencies in ways that seem most reasonable. 2) Concerning the hockey stick (which took up probably 3/4 of the review pages!): what Mike Mann continually fails to understand, and no amount of references will solve, is that there is practically no reliable tropical data for most of the time period, and without knowing the tropical sensitivity, we have no way of knowing how cold (or warm) the globe actually got. (And similarly, without knowing the tropical sensitivity for the LGM, we don't know what it's global cooling was, and without knowing it for 2xCO2, we don't know what the future sensitivity would be.) It cannot be reconstructed with any confidence from the extratropical response, even if we were to know that well, because the extratropical response is partly driven by in situ feedbacks, so can occur with a variety of tropical responses. [We have a paper in press (two papers, actually), discussing this aspect - I've actually sent them to IPCC and several of the chapter leads with respect to their discussions of AO/NAO variations with climate.] Therefore the detailed comments Mike provides concerning the extratropical issues - how much does snow cover alter the ground temperature versus the surface air temperature - are to some extent beside the point. I've made the comment to Mike several times, but it doesn't seem to get across - during the 20th century, according to Jim Hansen's temperature reconstruction, the tropical warming has been 60% of that in the extratropics (and that includes the amplifying AO/NAO extratropical change). I believe that in Mike's reconstruction, it averages about 30%. How well we know the numbers for the first part of this century is also somewhat uncertain, so I can't say Mike is wrong - but the point is, I don't know that he's right, nor do I think anybody else knows either. So what should we do about it? Basically I think we should indicate that there are conflicting views concerning the actual global climate change during this time period - quote the references (including the one's Mike provides), note that there are uncertainties concerning the magnitude of the extratropical response, and that there is a paucity of tropical data - and leave it at that. Unsatisfying, perhaps, since people will want to know whether 1200 AD was warmer than today, but if the data doesn't exist, the question can't yet be answered. A good topic for needed future work. 3) Concerning Mike's comment about the importance of volcanism for the 17th century cooling - again, what is the evidence for the aerosol optical depth? Everything is indirect, so much so that different authors come up with very different values, as I've quoted in the chapter. The safest and most honest approach for this and other similar subjects, is that when something is uncertain we should say it. I know uncertainty lies in the eyes of the beholder, but I think it will also be found in the eyes of the reviewers, and here I would suggest a democratic approach - let's not use one person's dogmatic view, but by quoting what the community thinks (as in the case of solar forcing), let the uncertainty be made apparent. And if there is uncertainty in the ice sheet reconstruction (e.g., how different are the U of Maine results), we should say that as well. I'm not suggesting we don't use our understanding to evaluate what has been published - if it is clear to the community as a whole that a segment of the differing results are clearly inferior, we should say that - and offer the proof the community has provided. 4) And the question of dogmatism versus uncertainty extends to modeling results, particularly (though not only) in the case of EMIC results, and results using coupled ice sheet models, or vegetation models (e.g., Colin Prentice's comments). Both mechanistically and theoretically, there are major uncertainties in the results from such models - matching of time scales and resolution for ice sheets, understanding the way plants actually operate, and all the simplifications inherent in EMICs - these should be emphasized to be conceptual results primarily. I discussed this at some length with Peter Stone, who himself runs an EMIC, and is very familiar with all of them, and he agreed entirely. What this means in practice is that results that are obtained through the use of such models not be given the dogmatic air of 'explaining' the problem, but rather of suggesting an explanation. It leaves the question open for further understanding, which I think is the most accurate approach. For GCMs, as in the prediction chapter, the use of a variety of models giving different answers already makes it clear that there is uncertainty in their results. That covers the majority of the comments. Note that "Batch B" is not about our chapter, as far as I could tell. David -- 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/ _______________________________________________ Wg1-ar4-ch06 mailing list Wg1-ar4-ch06@joss.ucar.edu http://www.joss.ucar.edu/mailman/listinfo/wg1-ar4-ch06