From: Jonathan Overpeck To: Eystein Jansen Subject: Re: Bullet debate number 2 Date: Wed, 15 Feb 2006 16:36:46 -0700 Cc: Keith Briffa thanks. Agree on the attribution front, but what about being more specific (at least a little) about what the "subsequent evidence" is. Is there really anything new that gives us more confidence? Keith? Eystein? thx, peck Hi, I think this version of bullett two is best: o The TAR pointed to the "exceptional warmth of the late 20th century, relative to the past 1000 years". Subsequent evidence reinforces this conclusion. Indeed, it is very likely that average Northern Hemisphere temperatures during the second half of the 20th century were warmer than any other 50-year period in the last 500 years. It is also likely that this was the warmest period in the past 1300 years . The uneven coverage and characteristics of the proxy data mean that these conclusions are most robust over summer, extra-tropical, land areas. I agree with Keith we cannot enter into the attibution aspects that Susan alludes to. Eystein At 11:57 -0700 15-02-06, Jonathan Overpeck wrote: Hi again - as for bullet issue number 2, I agree that we don't need to go with the suggest stuff on solar/forcing, BUT, I agree w/ Susan that we should try to put more in the bullet about "Subsequent evidence" Would you pls send a new bullet that has your suggested changes below, and that includes something like: "Subsequent evidence, including x, y and z, reinforces this conclusion." Need to convince readers that there really has been an increase in knowledge - more evidence. What is it? The bullet can be longer if needed. Thanks, Peck Second Simply make "1000" "1300 years. " and delete "and unusually warm compared with the last 2000 years." It is certainly NOT our job to be discussing attribution in the 20th century - this is Chapter 9 - and we had no room (or any published material) to allow a discussion of relative forcing contributions in earlier time. Therefore a vague statement about "perhaps due to solar forcing" seems unjustified. Third I suggest this should be Taken together , the sparse evidence of Southern Hemisphere temperatures prior to the period of instrumental records indicates that overall warming has occurred during the last 350 years, but the even fewer longer regional records indicate earlier periods that are as warm, or warmer than, 20th century means. Fourth fine , though perhaps "warmth" instead of "warming"? and need to see EMIC text Fifth suggest delete Sixth suggest delete Peck, you have to consider that since the TAR , there has been a lot of argument re "hockey stick" and the real independence of the inputs to most subsequent analyses is minimal. True, there have been many different techniques used to aggregate and scale data - but the efficacy of these is still far from established. We should be careful not to push the conclusions beyond what we can securely justify - and this is not much other than a confirmation of the general conclusions of the TAR . We must resist being pushed to present the results such that we will be accused of bias - hence no need to attack Moberg . Just need to show the "most likely"course of temperatures over the last 1300 years - which we do well I think. Strong confirmation of TAR is a good result, given that we discuss uncertainty and base it on more data. Let us not try to over egg the pudding. For what it worth , the above comments are my (honestly long considered) views - and I would not be happy to go further . Of course this discussion now needs to go to the wider Chapter authorship, but do not let Susan (or Mike) push you (us) beyond where we know is right. -- 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/ -- ______________________________________________________________ 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 -- 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/