date: Thu, 01 May 2003 10:27:12 +0100 from: Tim Osborn subject: Re: Mike Mann's review to: Phil Jones ,k.briffa@uea.ac.uk Phil & Keith, here are my suggestions for how to deal with Mike's comments - though we might want to wait for other review before doing anything. (1) Valid point but easy to deal with by adding something like... "without more widespread data we don't know how general these changes are, but if they are applicable to other parts of the world then there are two principal implications..." (2) Don't get into discussion right at the beginning on which reconstructions are results are applicable to; instead change meaning of our first sentence by "...Briffa and Osborn (2002) noted that IF reconstructions of annual temperature trends (for parts of the last millennium) ARE based on predictors that are strongly influenced by summer conditions, THEN THEY tacitly...." Then expand the discussion section (see point 8 below) to mention some particular reconstructions and perhaps that the potential bias is less for those that use more non-summer-sensitive proxies. (3) Worth doing the composites as they're easy to do - (if the composite does look like the NH-mean, then we can call it yet another NH reconstruction!). (4) Some discussion of forcing vs. internally generated influences on seasonal differences could go in the discussion section (as I suggested prior to submission!) (5) Do you have these N. American series Phil? Are they long enough to tell us more than is already in the NH network? (6) Just cite Shindell et al. as an example where we say that seasonal differences are a good diagnostic for testing model performance, for model runs of the last millennium. (7) Not sure whether we want to detrend or not, since the trend itself is part of the signal we're after reconstructing. But certainly we could discuss that fig. 3 is based on 20th century variations and the seasonal-annual relationships may well differ in other centuries which don't have such strong anthropogenic forcing. This is, of course, the whole point of the paper, that seasonal-annual relationships may not be stationary! (8) In the discussion section I think we can expand things to make the caveat that not all proxies are summer sensitive and therefore some reconstructions may not be biased by seasonality changes so much (e.g., Mann et al., 1998). But then go on to note that this probably doesn't mitigate the bias early on when the corals and the TexMex tree-rings aren't available (e.g., Mann et al., 1999), and therefore are results are valid to that - and that early bit is the crucial bit when claiming that 20th century temperatures are warmest in the millennium! (9) This will all have been covered by the above. What do you think? Cheers Tim Dr Timothy J Osborn | phone: +44 1603 592089 Senior Research Associate | fax: +44 1603 507784 Climatic Research Unit | e-mail: t.osborn@uea.ac.uk School of Environmental Sciences | web-site: University of East Anglia __________| http://www.cru.uea.ac.uk/~timo/ Norwich NR4 7TJ | sunclock: UK | http://www.cru.uea.ac.uk/~timo/sunclock.htm