cc: tom@ocean.tamu.edu,td@gfdl.gov, Malcolm Hughes ,mann@virginia.edu, rbradley@geo.umass.edu,k.briffa@uea.ac.uk date: Thu, 01 Mar 2001 12:08:02 +0000 from: Phil Jones subject: Re: letter to Science to: "Michael E. Mann" , "Henry N. Pollack" , "Michael E. Mann" Dear Mike et al, Here's my input. I'll be here tomorrow till about 11am British time then I'm away all next week. Maybe you'll have time to do something today and email another copy at the end. First a minor thing. Science's new endnote style means that you can have only one reference in each and a wordy endnote with a reference has to have this referenced as a separate endnote. So you'll need to be very careful which 15 or so are chosen. Two other small things. First we should not stoop to the skeptic level and use the phrase 'hockey stick' in print. Just say recent. Also I think the references you do use should be mostly earlier ones than 1999 or 2000 (except for our few recent compilation papers) so they are clearly references that have been around sometime and if Broecker is going to write such an article he should have been aware of. Specific points. First, I think it is a bit long - I'll suggest reductions. 1. Sentence 2 'To reach this conclusion ...' . Add in here that these records are calibrated against instrumental records. Just say ... that are calibrated against instrumental records and are the foundation ... Could add and verified as well after calibrated. This will make it clear in the second sentence that Broecker is rejecting the standard practice in much of paleoclimatology. 2. Just reference Hughes and Diaz (possibly Lamb as well) re MWP. After this sentence could say: The two warming periods (~1920-45 and since 1975) in the 20th century show patterns of warming (which predominate) but there are a few regions that show cooling. Even during these two strong warming periods (~0.4C over the NH) few of temperature trends are locally significant ( Jones et al., 1999 Rev Geophys.) . 3. The final sentence of (1) is the most important of all. Needs to be emphasised and expanded upon. Thompson estimates that some of these ice caps/glaciers (which have ice layers in the Middle Ages) will disappear in the next 20 years. This is our best piece of evidence. I know we don't use them in many of the compilations, but if these areas had layers in the Middle Ages and are disappearing arguments that globally it was warmer in the MWP are shot to pieces. 4) Remove the whole of the middle of section (2) from Cook to the sentence begining 'Several.. ' . This material was in the papers but it didn't convince Broecker then, so it's not worth repeating here. Just reference Cook - not the seg length curse, and possibly add Briffa et al (2001) if this is out in JGR. Don't say that dendroclimatologists always take these trends into account in interpretation because they clearly don't. Try and keep the text short, pointed and don't leave ends that can be used against us. I'd make the points after several into a different bullet point. This just needs to say that even the LIA wasn't ubiquitous cold from the 15th to the 19th centuries. The 'near instrumental' period - trying to think of name like the Middle Ages for the MWP to use instead of LIA - is characterised in many regions by a cool 17th and 19th centuries and a milder 18th century. It wasn't ubiquitously cold. Long European temperature records clearly show this - and they agree with borehole evidence back to 1659. 5. The glacier point could perhaps be a separate bullet. Broecker here thinks you can develop an NH glacial record which he says can be related to temperatures. Glaciers respond mainly to summer temperatures. Need to compare single glaciers or a regional average if they respond similarly. They can't be lumped. The reference is for northern Fennoscandia : Raper, SCB, Briffa, KR and Wigley, TML, 1996 J. Glaciology 42, 341-351. 6. (3) is mostly OK. Need to say decadal-scale variance. Also we know from the instrumental period that the two main factors explaining much of the variability are solar and volcanoes. Why bring in something else before you've exhausted these two. Solar is the important one here. The record isn't great but it is the best we have. It is a good job the 14C or 10Be records didn't have a 1500 yr cycle as Broecker would have had the cause of his supposed 'cycle' . He has looked for this, but can't find anything. 7 (4) I think the first part of this is week and like the arm-waiving we are accusing Broecker of. Hopefully Tom Delworth can help here. I don't know much about this, but what is there doesn't sound at all convincing. 8 (4) Second part. Isn't that convincing either. Final para is fine. Cheers Phil At 13:35 28/02/01 -0500, Michael E. Mann wrote: Hi Henry, None of us are disputing that conditions were relatively warmer in the earlier centuries (ie, 11th-14th) than in the later centuries (15th-19th), but the main point is that they were not as warm as the latter 20th century. At the face of it, your GRL article does certainly seem to suggest otherwise, and this how Wally has interpreted it. My point was that there is a sensitivity of that conclusion to a priori constraints. What we need then is a clear and defensible statement from you as to why that paper isn't in conflict with what we're saying. If you can suggest a specific rephrasing to replace what we have, I would appreciate that. I thought you and Tom had already consulted on this, but perhaps I'm mistaken. Thanks in advance, mike At 01:22 PM 2/28/01 -0500, Henry N. Pollack wrote: Hello everyone! On Wed, 28 Feb 2001, Michael E. Mann wrote: > ........................................... Although one analysis of > heat flow measurements suggests warmer temperatures than the surface > proxies during the Middle Ages (Huang and Pollack, GRL. 1997), the > considerable sensitivity of the resulting trends to a priori statistical > assumptions has lead borehole researchers to restrict their attention to > the more reliably interpretable temperature fluctuations during the past > five centuries (Huang and Pollack, Nature). ......................... Henry Pollack comments on the above statement: Linking the two geothermal studies (1997, 2000) is not quite kosher. We did not later "restrict our attention" to the last five centuries because of the considerable sensitivity to the a priori assumptions in the 1997 GRL paper. Throughout the range of the a priori assumptions there is an indication of warmth in the middle ages. But as I mentioned in my comments to Tom Crowley yesterday, whether that warmth exceeded the end-of-20th century temperatures is perhaps debatable. I said to Tom that the hockey stick will not rise or fall on the basis of the 1997 GRL paper that analyzed heat flow variations with depth. Our later emphasis on the past five centuries was intended to bring into sharper focus the late pre-industrial and industrial eras. The five century study reported in Nature used much higher quality data, actual temperature vs. depth data rather than inferred heat flow vs. depth data. It is no secret that the results of this five century study show some disagreement with the hockey stick also, in the magnitude and timing of the LIA minimum. That is another issue, not one directly addressing Wally Broecker's discussion of the MWP. Cheers, Henry p.s. I will be traveling as of this afternoon (2/28), returning on 3/5. I would be grateful to receive a final copy of what you submit, but respectfully decline to sign on as a co-author. _______________________________________________________________________ Professor Michael E. Mann Department of Environmental Sciences, Clark Hall University of Virginia Charlottesville, VA 22903 _______________________________________________________________________ e-mail: mann@virginia.edu Phone: (804) 924-7770 FAX: (804) 982-2137 [1]http://www.evsc.virginia.edu/faculty/people/mann.html Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email p.jones@uea.ac.uk NR4 7TJ UK ----------------------------------------------------------------------------