cc: mann@virginia.edu
date: Sat, 12 Jul 2003 00:07:37 -0400
from: "Michael E. Mann" <mann@virginia.edu>
subject: Re: query regarding Soon et. al. rebuttal
to: "Regalado, Antonio" <Antonio.Regalado@wsj.com>

   Dear Antonia,
   Thanks for your message. Happy to hear your thinking of doing this article.
   Just got back from Japan, so a bit jet lagged, but wanted to at least get an initial
   response to you. Please feel free to contact me over the weekend, by email or otherwise, if
   I can be of further help.
   Some specific comments below.
   best regards,
   Mike M
   At 04:17 PM 7/11/2003 -0400, you wrote:

     Prof. Mann,
     Hi from the Wall Street Journal. I am thinking of citing your rebuttal to
     Soon et. al. in a news item I am writing for the newspaper.
     You say that it is "only the past few decades druging which n. hemisphere
     temperatures have exceeded the bounds of natural variability...". Do you
     mean the last few decades are the warmest of the last millennium only, not
     all of time, right?

   yes, in fact, though, we can now say with a reasonable degree of confidence that Northern
   Hemisphere mean temperatures were higher during the past two decades than any other
   interval during at least roughly the past *two* millennia  (the extension to the past two
   millennia is afforded by a paper in press in the journal 'Geophysical Research Letters' by
   Phil Jones and myself--a result of that paper was shown in our 'Eos' piece, but we'll issue
   a more specific press release on that result when the paper is slated to appear in a few
   weeks). Its unclear how Northern Hemisphere average temperature (let alone global average
   temperature) varied during prior millennia  (see below).

     To what degree are n. hemisphere temperatures anomalous
     when compared to the entire paleoclimate record?

   Its *possible* the conclusion holds for the last 6000 years, or even longer, but that's
   speculative.  When we go back beyond the past one or two millennia, the issue gets very
   tricky--we no longer have annually-detailed proxy records which we can compare directly
   against modern thermometer records. It is possible to do so with very long
   annually-resolved ice cores, tree-rings, corals, and  historical records, which give us a
   picture of changes over the past one-to-two millennia, but not with the sorts of evidence
   (pollen, ocean sediments, coursely-resolved ice cores, glacial advances and retreats) that
   are available to provide longer-term insights. There is a good discussion of these issues
   in the 2001 IPCC report, if you would like some additional detailed information:
   [1]http://www.grida.no/climate/ipcc_tar/wg1/068.htm
   That having been said, the 'mid-Holocene' interval (about 6000 years ago) when the
   astronomical factors influencing the climate favoured greater insolation in the Northern
   Hemisphere summer, might have been warmer than the late 20th century. The available
   evidence, though limited, suggests this--and a number of older model simulations suggested
   that might be the case. Some recent work, using the best available current climate models,
   suggests, however, that the temperatures were perhaps comparable to today back then. There
   was another period prior to the last Ice Age (more than 120,000 years ago) called the
   'Eemian' for which there is  tentative evidence that global mean temperatures might have
   been even higher than during the mid-Holocene. But 'tentative' is the key phrase--the
   evidence is often restricted in where its available, and whether its telling us about
   annual conditions (what we would like to know) or only, say, summer growing season
   conditions.
   It is almost certain that global mean temperatures were warmer during certain past
   geological periods (e.g., the Cretaceous, when we suspect that Co2 levels were higher than
   today, and that the globe, w/ Dinosaurs wandering around near the poles, was almost
   certainly warmer). These changes occurred over many millions of years, due to the influence
   of plate motion on the production of co2 by geological sources (e.g. volcanic outgassing).
   Of course, that warming occurred over many millions of years. The present warming is
   occurring on a century time scale, so it is the *rate* of recent warming that may be
   particularly anomalous in the long-term history of the climate.

     Also, when was the last time C02 levels were as high as they are now, do you
     know?

   There is still some debate about this. We now have excellent CO2 records from ice cores
   dating back to more than 400,000 years. The present Co2 concentration appears higher than
   at any time during that record. The longer-term evidence is more tenuous (based on trace
   gases trapped in ambers, evidence from fossil leaf stomata, etc.), but it is quite likely
   that co2 levels were higher as one gets back towards the Cretaceous period (e.g. more than
   50 million years ago), precisely how much higher is still a subject of dispute. The present
   thinking is that current co2 levels are probably the highest in about 20 million years. See
   again e.g. the IPCC 2001 report for details:
   [2]http://www.grida.no/climate/ipcc_tar/wg1/107.htm#331

     Thanks

   happy to be of help

     Antonio Regalado
     Staff Reporter, The Wall Street Journal
     212-416-3011 (Tel.)
     917-686-3389 (Cell)

   ______________________________________________________________
                       Professor Michael E. Mann
              Department of Environmental Sciences, Clark Hall
                         University of Virginia
                        Charlottesville, VA 22903
   _______________________________________________________________________
   e-mail: mann@virginia.edu   Phone: (434) 924-7770   FAX: (434) 982-2137
            [3]http://www.evsc.virginia.edu/faculty/people/mann.shtml

