From: "Michael E. Mann" <mann@multiproxy.evsc.virginia.edu>
To: Phil Jones <p.jones@uea.ac.uk>
Subject: Re: Wally
Date: Mon, 26 Feb 2001 09:03:51 -0500
Cc: mhughes@ltrr.arizona.edu, tom crowley <tom@ocean.tamu.edu>,  rbradley@geo.umass.edu, tom@ocean.tamu.edu, k.briffa@uea.ac.uk,  t.osborn@uea.ac.uk, mann@virginia.edu

Dear Phil,

Thanks for your response. I agree that I think these folks just don't quite
seem to get it! Anyways, I've pasted in the text of Broecker's piece below
(everything there but the figure. Trust me, the figure isn't worth looking
at anyways). Will be very interested to hear your thoughts after reading
this...

mike

PALEOCLIMATE:
 Was the Medieval Warm Period Global?

 Wallace S. Broecker*

 The reconstruction of global temperatures during the last millennium can
provide important clues for how
 climate may change in the future. A recent, widely cited reconstruction
(1) leaves the impression that the
 20th century warming was unique during the last millennium. It shows no
hint of the Medieval Warm
 Period (from around 800 to 1200 A.D.) during which the Vikings colonized
Greenland (2), suggesting
 that this warm event was regional rather than global. It also remains
unclear why just at the dawn of the
 Industrial Revolution and before the emission of substantial amounts of
anthropogenic greenhouse gases,
 Earth's temperature began to rise steeply.

 Was it a coincidence? I do not think so. Rather, I suspect that the
post-1860 natural warming was the
 most recent in a series of similar warmings spaced at roughly 1500-year
intervals throughout the present
 interglacial, the Holocene. Bond et al. have argued, on the basis of the
ratio of iron-stained to clean
 grains in ice-rafted debris in North Atlantic sediments, that climatic
conditions have oscillated steadily
 over the past 100,000 years (3), with an average period close to 1500
years. They also find evidence for
 the Little Ice Age (from about 1350 to 1860) (3). I agree with the authors
that the swing from the
 Medieval Warm Period to the Little Ice Age was the penultimate of these
oscillations and will try to
 make the case that the Medieval Warm Period was global rather than regional.

 One difficulty encountered when trying to reconstruct Holocene temperature
fluctuations is that they were probably less than 1°C. In my
 estimation, at least for time scales greater than a century or two, only
two proxies can yield temperatures that are accurate to 0.5°C: the
 reconstruction of temperatures from the elevation of mountain snowlines
and borehole thermometry. Tree ring records are useful for measuring
 temperature fluctuations over short time periods but cannot pick up
long-term trends because there is no way to establish the long-term
 evolution in ring thickness were temperatures to have remained constant.
Corals also are not accurate enough, especially because few records
 extend back a thousand years. The accuracy of the temperature estimates
based on floral or faunal remains from lake and bog sediments is
 likely no better than ±1.3°C (4) and hence not sufficiently sensitive for
Holocene thermometry.

 The Mountain Glaciation Record
 At the Last Glacial Maximum, mountain snowlines throughout the world were
on average about 900 m lower than today (5). On the basis of
 today's rates of temperature change with elevation, this required an air
temperature cooling at the elevation of the glacier of about 5°C (and a
 corresponding tropical sea surface temperature cooling of about 3°C).
During the Younger Dryas--a cold "spell" of about 1200 years during the
 last deglaciation--snowlines in the Swiss and New Zealand Alps dropped to
about 300 m below the lowest levels reached in the subsequent
 Holocene.

 Since their 1860 maximum at the end of the Little Ice Age, the retreat of
Swiss glaciers represents a rise in snowline of about 90 m (6). If this
 rise could be attributed entirely to air temperature, the required warming
would be between 0.5° and 0.6°C. However, simple considerations
 suggest that precipitation changes result in a negative feedback of about
20% (7). The warming required to account for the post-1860 retreat of
 Alpine snowlines would then be between 0.6° and 0.7°C.

 The post-1860 glacier retreat is not confined to Switzerland. With the
exception of Antarctica, it has been well documented everywhere on
 Earth where ice-covered mountains are present (2). There is no doubt that
the Little Ice Age was global in extent and that the post-1860
 warming was also global. In this regard, the Mann et al. (1)
reconstruction is consistent with the mountain snowline record.

 The Medieval Warm Period has also left its traces in the Swiss Alps.
Holzhauser has reconstructed the history of a larchwood aqueduct
 constructed by medieval farmers (8). It ran from a small mountain lake
along the valley occupied by the Grosser Aletsch Glacier, supplying
 water to an Alpine village. The aqueduct was first constructed around 1200
A.D. (toward the end of the Medieval Warm Period). It was
 partially destroyed when the glacier advanced in 1240 A.D. and had to be
totally rerouted after a further advance in 1370 A.D.

 Swiss geologists and geomorphologists agree that the large moraines
marking the maximum glacier extent during the Little Ice Age are a
 composite of debris left behind by a series of Holocene advances (9). For
example, soils separating individual advance episodes have been
 found within the moraines. Precise dating has proven difficult, however,
and the chronology of these prior advances remains uncertain.

 Two recent studies of Holocene climate cycles in the Swiss Alps have
greatly improved this situation. Both focus on establishing the times of
 glacial retreats rather than advances. Holzhauser (8), on the basis of
radiocarbon dating of larchwood stumps exposed by the ongoing retreat of
 the Grosser Aletsch Glacier, finds warm episodes 2400 ± 300 and 1500 ± 200
calendar years ago. Hormes and Schlüchter (10-12) have dated
 wood and peat fragments that are being disgorged from beneath a number of
Swiss glaciers. Radiocarbon dates of a large number of these
 samples cluster in three major groups centered at 8700, 6600, and 4300
calendar years before present. The correlation between these Alpine
 warm phases and the warm phases of Bond's North Atlantic ice-rafting
record, although imperfect, is encouraging (see the figure).



 Climatic oscillations during the Holocene. Circles show the ratios of
iron-stained to total grains (for grains with diameters >63 mm) in a
 North Atlantic core (3). The chronology is taken from (22). The green
(10-12) and yellow (8) boxes are based on radiocarbon dating on wood
 and peat formed when the glaciers had retreated to positions similar to or
up-valley from those at present (see text). 

 CREDIT: FIGURE PREPARED BY AUTHOR FOR THIS PUBLICATION


 Borehole Thermometry
 Geothermal heat is produced deep inside Earth, and the shape of the
vertical temperature profile measured in a borehole from any point on
 Earth's surface thus reflects the depth dependence of the thermal
conductivity of the crustal material. The temperature at the surface does not
 remain constant, however, and the thermal profiles therefore have kinks
that reflect past air temperature fluctuations. Mathematical
 deconvolutions are used to reconstruct these fluctuations from the
temperature profile, but because of smoothing due to diffusive spreading of
 past thermal anomalies, many different time histories fit the observed
downhole temperature record. The modeler selects from these
 possibilities the temperature history with the least complicated shape.
The details are thus lost, and only the broad features of the time history
 are captured.

 Deconvolutions of thermal records from holes drilled through the polar ice
caps reveal broad maxima that reflect the colder temperatures during
 glacial times. In Greenland boreholes, this broad glacial feature is
preceded by a narrower one, which requires a temperature oscillation to have
 occurred in the late Holocene. The timing of this swing broadly matches
that of the Medieval Warm Period to Little Ice Age oscillation. Its
 magnitude is about 2°C (13). The borehole temperature record for Greenland
thus appears to reflect the climate changes thought to have led to
 the establishment and eventual abandonment of the Viking colonies in
southern Greenland (2). It is also consistent with records in the Swiss
 Alps.

 Far Field Evidence
 Evidence for the Medieval Warm Period from other parts of the world exists
but is spotty and/or circumstantial. From an analysis of 6000
 continental borehole thermal records from around the world (14), Huang et
al. conclude that 500 to 1000 years ago, temperatures were warmer
 than today, but that about 200 years ago, they cooled to a minimum some
0.2° to 0.7°C below present. However, as is the case for the thermal
 profiles in ice, those for continental boreholes are highly smoothed.
Although suggestive, the fluctuation postulated by Huang et al. does not
 prove that the Medieval Warm Period was global in extent.

 Evidence that climate during the latter part of the Medieval Warm Period
was much different from today's comes from moisture records for
 the western United States. Stine has studied lodgepole pine trees rooted
at 8 to 19 m depth in Lake Tenaya in the high Sierra Nevada (15). For
 the trees to have grown, the lake must have been nearly dry. In contrast,
only once during the past 50 years has the lake not overflown during
 snowmelt. Using radiocarbon dating and ring counting, Stine has shown that
for 70 years before 1093 A.D., the lake stood at least 13 m below
 its outflow spillway, and for 141 years before 1333 A.D., it stood at
least 11 m below its spillway (16). Stine has documented similar events at
 Mono Lake and the Walker River (17). He concludes that late in the
Medieval Warm Period, California experienced several decade-long
 periods of profound drought.

 If, as Bond et al. (3) suggest, the cyclic changes in ice-rafted debris
composition reflect oscillations in the strength of the Atlantic's conveyor
 circulation, one might expect temperature changes in Antarctica to have
been opposite in phase to those in the North Atlantic, as was the case
 during the last deglaciation (18). Clow has carried out a deconvolution of
the temperature record at the Antarctic Taylor Dome site (19). His
 reconstruction shows that the air temperature was 3°C colder during the
time of the Medieval Warm Period than during that of the Little Ice
 Age. This record suggests that conditions in Antarctica underwent an
antiphased oscillation during the Medieval Warm Period-Little Ice Age
 period.

 The Case for a Global Event
 The case for a global Medieval Warm Period admittedly remains
inconclusive. But keeping in mind that most proxies do not have adequate
 sensitivity, it is interesting that those capable of resolving temperature
changes of less than 1°C yield results consistent with a global Medieval
 Warm Period. To test whether this is indeed the case, we require Holocene
snowline fluctuation records for tropical and Southern Hemisphere
 sites and continued studies of wood and peat exposed by the continuing
retreat of Northern Hemisphere glaciers. As the world's mountain
 glaciers continue to retreat, ever more evidence for past Holocene warm
episodes will be exposed.

 One might ask why the strength of the Atlantic's conveyor circulation
oscillates on a time scale of one cycle per 1000 to 2000 years. I suspect
 that it has to do with the export through the atmosphere of water vapor
from the Atlantic to the Pacific Ocean. The magnitude of this export
 has been estimated to be (0.25 ± 0.10) x 106 m3/s (20). If this freshwater
loss were not balanced by the export of salt from the Atlantic, the
 latter's salt content would rise at the rate of about one gram per liter
each 1500 years. Such an increase in salt content would densify cold
 surface water by an amount equivalent to a 4 to 5 K cooling, thereby
strongly altering the buoyancy of surface waters in the North Atlantic and
 hence their ability to sink to the abyss.

 I believe that this salt export is not continuous but episodic. The salt
content of the Atlantic periodically builds up until a strong conveyor
 circulation mode is turned on, causing the salt content to drain down.
Eventually, a weak circulation mode kicks in, allowing the salt content to
 build up again. I have suggested previously (21) that an apparent mismatch
between radiocarbon and chlorofluorocarbon-based estimates of the
 rate of deep-water formation in the Southern Ocean may reflect a change in
circulation after the Little Ice Age.

 The geographic pattern of Holocene climate fluctuations remains murky, but
several things are clear. The Little Ice Age and the subsequent
 warming were global in extent. Several Holocene fluctuations in snowline,
comparable in magnitude to that of the post-Little Ice Age warming,
 occurred in the Swiss Alps. Borehole records both in polar ice and in
wells from all continents suggest the existence of a Medieval Warm
 Period. Finally, two multidecade-duration droughts plagued the western
United States during the latter part of the Medieval Warm Period. I
 consider this evidence sufficiently convincing to merit an intensification
of studies aimed at elucidating Holocene climate fluctuations, upon
 which the warming due to greenhouse gases is superimposed.

 References and Notes

    1.M. E. Mann, R. S. Bradley, M. K. Hughes, Geophys. Res. Lett. 26, 759
(1999) [ADS]. 
    2.J. M. Grove, The Little Ice Age (Methuen, New York, 1988), pp. 1-198. 
    3.G. C. Bond et al., Mechanisms of Global Climate Change at Millennial
Time Scales, Geophysical Monograph Series, vol. 112
      (American Geophysical Union, Washington, DC, 1999), pp. 35-58
[publisher's information]. 
    4.A. Lotter et al., Palaeogeogr. Palaeoclimatol. Palaeoecol. 159, 349
(2000) [GEOREF]. 
    5.S. C. Porter, Quat. Sci. Rev., in press. 
    6.M. Maisch et al., Die Gletscher der Schweizer Alpen (Hochschulverlag
AG an der ETH Zürich, Zürich, 1999), pp. 221-256. 
    7.M. Greene, W. S. Broecker, D. Rind, Geophys. Res. Lett. 26, 1909
(1999) [ADS]. 
    8.H. Holzhauser, in Paläoklimaforschung Palaeoclimate Research 24,
Special Issue: ESF Project "European Palaeoclimate and Man
      16," B. Frenzel et al., Eds. (Verlag, Stuttgart, 1997), pp. 35-58. 
    9.F. Rothlisberger et al., Geogr. Helv. 35/5, 21 (1980). 
   10.A. Hormes, The 14C Perspective of Glacier Recessions in the Swiss
Alps and New Zealand (Verlag, Osnabrück, Germany, 2001),
      p. 176. 
   11.A. Hormes, C. Schlüchter, T. F. Stocker, Radicarbon 40, 809 (1998). 
   12.A. Hormes, B. U. Müller, C. Schlüchter, Holocene, in press. 
   13.E. J. Steig et al., Science 282, 92 (1998). 
   14.S. Huang, H. N. Pollack, P. O. Snen, Geophys. Res. Lett. 24, 1947
(1997) [ADS]. 
   15.S. Stine, in Water, Environment and Society in Times of Climatic
Change, A. S. Issar, N. Brown, Eds. (Kluwer Academic,
      Amsterdam, Netherlands, 1998), pp. 43-67 [publisher's information]. 
   16.The level that would have existed had there been an annual
snowmelt-induced overflow. 
   17.S. Stine, Nature 369, 546 (1994) [GEOREF]. 
   18.W. S. Broecker, Paleoceanography 13, 119 (1998) [ADS]. 
   19.G. Clow, personal communication. 
   20.F. Zaucker, W. S. Broecker, J. Geophys. Res. 97, 2765 (1992) [ADS]. 
   21.W. S. Broecker, S. Sutherland, T.-H. Peng, Science 286, 1132 (1999). 
   22.M. Stuiver et al., Radiocarbon 40, 1041 (1998). 


 The author is at Lamont-Doherty Earth Observatory, Columbia University,
Palisades, NY 10964, USA. E-mail: broecker@ldeo.columbia.edu

At 12:04 PM 2/26/01 +0000, Phil Jones wrote:
>
>  Dear All,
>       I was away over the weekend at Bowdoin College in Maine, giving a 
>talk about the
>  last 1000 years. There were three others as well on other paleo aspects, 
>Richard Alley,
>  Gary Clow and Wally Broecker !  The latter briefly mentioned to me that 
>he had had
>  something in last Friday's Science, which was getting at the Mann et al. 
>series. He
>  didn't have a copy so we've not seen it here yet.  I tried to get a copy 
>of Science on
>  the bookstand at Logan airport last night - I guess it's not sold that
way !
>      Wally was going on about this 1500 yr cycle of Bond's, which seemed 
>pretty flimsy.
>  I was showing all the various series in a general talk - and I used some 
>of the overheads
>  from the upcoming Science paper. This is due to appear in the issue for 
>the last week
>  of April. It is all accepted now.  I will forward if you'll all abide by 
>the Science rules. Both
>  Wally and Alley seem convinced that the climate of Greenland changed by 
>10 C in
>  the space of 2-3 years at times in the past (Y Dryas etc).  I had long 
>talks with both
>  and they don't seem to have got their heads around spatial scales (local 
>changes
>  and hemispheric). Also they don't seem to realise where we are coming 
>from.  He
>  has a downer on trees (believes all the multiproxy series depend 
>exclusively on
>  trees) but he thinks Ed Cook is a great scientist. The latter is true, 
>but he might
>  just think that because he's at Lamont. I did tell him that Keith's paper 
>on the age
>  banding is out in JGR. I should send him a reprint and maybe ask that great
>  scientist to go and explain it to him ! Ed's in NZ at the moment. Also 
>Wally believes
>  much more in glacier advances/retreats. I'll get Keith to send him 
>Sarah's paper
>  where the long Tornetrask reconstruction is shown to agree with
Storglaciaren
>  advance/retreat dates from moraine evidence. Also Sarah's been working on 
>similar
>  glaciers in the Swiss Alps with long tree-ring reconstructions.  One 
>interesting
>  thing was he didn't seem to realise that a lot of the tree-ring 
>reconstructions use
>  density. Seemed to think they were all ring widths and there had to be 
>moisture
>  changes we were not accounting for.
>        It is easy to respond to a Perspectives piece. Some of you did it 
>with respect to
>  one of mine. I'm not sure it will achieve much - it won't come out before 
>the paper
>  in the last week of April.  I need to wait to se what he says. Our paper 
>(me, Tim and
>  Keith) clearly says that the MWP couldn't have been warmer (for the NH 
>average)
>  than the late 20th century.
>       Another possible reason for not doing anything is that the IPCC 
>report will be out
>  soon. The summary is written in pretty clear language.
>      The above is my first thoughts, not having read the piece and just 
>got off the
>  flight back.
>
>      Best to ignore Woijcek. All he seems to want to do is deflect us into 
>responding.
>
>  Cheers
>  Phil
>
>
>
>At 11:47 25/02/01 -0700, mhughes@ltrr.arizona.edu wrote:
>>Dear all,
>>WHat mechanism does "Science" have for repsonding to Perspective pieces?
Most
>>of the answer to Wally is contained within his own piece - he comments on
the
>>ambiguity of the record, which, in various ways, we have all done. What he
>>doesn't offer, however, is anything other than an anecdotal alternative. As
>>always, he seeks to damn ( in this case with faint praise) the records or 
>>work
>>that don't serve his purpose , and to elevate any scrap of evidence that
does
>>serve it. I think it will be important for us to stick closely to what we 
>>have
>>written in published papers. CHeers, MAlcolm
>>
>>Quoting "Michael E. Mann" <mann@virginia.edu>:
>>
>> > Dear Phil, Ray,
>> >
>> > What do you guys think. If we're all on board, than an appropriately
>> > toned,
>> > "high road" response here might be appropriate. We don't want to engage
>> > Wally in a personal battle, but simply should correct the record where
>> > Wally has muddied it. Again, Phil et al do have a Science article in
>> > press
>> > that serves this purpose to some extent, so I'm especially interested in
>> > what
>> > Phil thinks (Phil?)...
>> >
>> > mike
>> >
>> > At 02:52 PM 2/24/01 -0700, mhughes@ltrr.arizona.edu wrote:
>> > >Dear Mike et al., I think we should definitely let Wojick stew in his
>> > own
>> > >juice - as Mike pointed out to me the other day he, and his like, have
>> > a
>> > >specific agenda, and anything we write will be pressed into the service
>> > of
>> > that
>> > >agenda. I'm not so sure about Wally. I share Tom's disinclination to
>> > get
>> > into a
>> > >street fight with Wally - generally I take the view that life's too
>> > short and
>> > >uncertain for such activities. On the other hand, would we let such a
>> > shoddy
>> > >piece of work(and editing) go by if it were from another author? There
>> > are so
>> > >many holes in Wally's argument, and such a selective choice of evidence
>> > that it
>> > >should beggar belief. One of the more obvious holes is that he writes
>> > of the
>> > >Great Basin droughts of the 10th through 14th centuries as proof of
>> > warmer
>> > >conditions then, but doesn't explain why we don't have such conditions
>> > now.
>> > >Interestingly, Larry Benson, Dave Meko and others have good evidence
>> > that
>> > these
>> > >same multidecadal periods were marked by a great excess of
>> > precipitation
>> > just a
>> > >few hundred miles north in northern Nevada and California and southern
>> > Oregon.
>> > >He just hasn't grasped that the methods that are appropriate for
>> > tracking the
>> > >consequences of major changes in boundary conditions don't work in the
>> > late
>> > >Holocene. I've been trying to figure out the issue of "Was there a
>> > Medieval
>> > >Warm Period, and if so where and when" for a decade or so, and still
>> > have the
>> > >impression that the records for the 9th through 14th centuries are
>> > extremely
>> > >mixed. But then, I didn't come to the investigation with a certain
>> > knowledge of
>> > >the absolute truth, and have had to 'misfortune' to work with people
>> > who let
>> > >careful analysis get in the way - Henry Diaz, Ray and Mike, and others.
>> >
>> > >Anyway, the point of this rant is that I think we should give careful
>> > >consideration to making a measured response to Wally. Cheers, Malcolm
>> > >
>> > >
>> > >
>> > >
>> > >Quoting "Michael E. Mann" <mann@virginia.edu>:
>> > >
>> > >> Hi Tom,
>> > >>
>> > >> Thanks for your quick reply. I agree with you entirely. I think its
>> > very
>> > >> unfortunate he's chosen to disinform the community rather than engage
>> > in
>> > >> a
>> > >> constructive dialogue (we tried the latter w/ him in a series of
>> > emails
>> > >> last
>> > >> year, but clearly to no avail).
>> > >>
>> > >> On the other hand, think that a war of words w/ Broecker would be
>> > >> exploited
>> > >> by the skeptics, and perhaps we should just try to let this thing
>> > die...
>> > >>
>> > >> I'm not sure. I'd appreciate knowing what others think?
>> > >>
>> > >> mike
>> > >>
>> > >> At 10:25 AM 2/24/01 -0600, tom crowley wrote:
>> > >> >Mike,
>> > >> >
>> > >> >I was not aware of the Broecker piece - I am dismayed but not
>> > >> surprised.  I
>> > >> >do not know what to do - I personally cannot stand the combative
>> > >> personal
>> > >> >approach Broecker relishes but it does seem as if some rebuttal is
>> > >> called
>> > >> >for.  Maybe you Ray Phil I and Malcolm could pen a response - we are
>> > >> >heading to Germany in a week, for a month, so I am not sure how much
>> > I
>> > >> can
>> > >> >keep up on this but it seems as if some response is called for.
>> > >> >
>> > >> >What think ye?
>> > >> >
>> > >> >Tom
>> > >> >
>> > >> >
>> > >> >>Dear Mike,
>> > >> >>
>> > >> >>Thanks for passing this along.
>> > >> >>
>> > >> >>Wojick of course completely misrepresents Broecker, and puts his
>> > >> >>conventional intellectually dishonest spin on this.
>> > >> >>
>> > >> >>That having been said, it is a bit disappointing that Wally
>> > continues
>> > >> to
>> > >> >>cling to some of his flawed beliefs which aren't supported from
>> > either
>> > >> our
>> > >> >>best current understanding of the observations or of the results of
>> > >> careful
>> > >> >>modeling experiments. My own perception is that the climate
>> > community,
>> > >> >>modelers as well as observationalists, simply don't take seriously
>> > >> anymore
>> > >> >>the idea that the history of climate change over the past 1000
>> > years
>> > >> is
>> > >> >>part of an internal oscillation. The sediment core evidence oft
>> > cited
>> > >> by
>> > >> >>Broecker (e.g. Bond et al) for this is tremendously weak, and I, as
>> > >> well as
>> > >> >>the vast majority of my colleagues, simply don't buy it for even a
>> > >> second.
>> > >> >>But people don't like to challenge Broecker publically. He can and
>> > >> will
>> > >> >>play hardball.
>> > >> >>
>> > >> >>There is an odd irony. Broecker refused to accept the modeling
>> > >> evidence
>> > >> >>that the 100 kyr ice age Pleistocene variations were part of an
>> > >> internal
>> > >> >>oscillation paced by insolation variations, favoring instead the
>> > >> >>discredited notion that they were a direct response to (too weak)
>> > >> >>eccentricity forcing, until the evidence became insurmountable
>> > (from
>> > >> my
>> > >> >>adviser, Barry Saltzman, may he rest in piece, and people like Dick
>> > >> >>Peltier). Ironically, Broecker then took credit for the very
>> > >> proposition he
>> > >> >>had fought w/ tooth and nail.
>> > >> >>
>> > >> >>Broecker is even more wrong, and unfortunately equally stubborn, in
>> > >> this case.
>> > >> >>And, again, the reason: because his pet theory, that climate
>> > >> variability is
>> > >> >>a simple millennial oscillation, is finally being challenged w/
>> > hard
>> > >> data
>> > >> >>and hard facts.
>> > >> >>
>> > >> >>Broecker misrepresents the nature of that data that we and others
>> > have
>> > >> >>used, and misunderstands the source of the muted hemispheric trends
>> > >> (there
>> > >> >>*is* a hemispheric "medieval warm period" and "little ice age",
>> > just
>> > >> not of
>> > >> >>the magnitude or the distinctiveness that Broecker imagines).
>> > >> Individual
>> > >> >>regions in our reconstructions, and Phils, and others, vary by
>> > several
>> > >> >>degrees C, ie, the proxies we use have no problem whatsoever in
>> > >> resolving
>> > >> >>high-amplitude temperature variations in the past. The problem is
>> > that
>> > >> when
>> > >> >>we look at  the different regions we find that periods of cold and
>> > >> warm
>> > >> >>often occur at very different times in different regions, and so in
>> > a
>> > >> >>hemispheric or global average, a lot of purely regional variability
>> > >> cancels
>> > >> >>out. The resulting trends are somewhat smaller. I remained
>> > befuddled
>> > >> as to
>> > >> >>why Wally doesn't understand this point. Its been explained to him
>> > >> time and
>> > >> >>time again. Maybe he's just not listening, or doesn't want to
>> > >> listen...
>> > >> >>
>> > >> >>In fact, Tom Crowley has clearly shown that the observed millennial
>> > >> >>temperature reconstruction is precisely consistent w/ our
>> > >> understanding of
>> > >> >>*forced* climate change over the past 1000 years (solar changes,
>> > >> volcancic
>> > >> >>output, and recent greenhouse gas concentrations). There is, simply
>> > >> put, no
>> > >> >>room for a global millennial internal oscillation. Regionally, such
>> > >> types
>> > >> >>of climate phenomena, associated for example with changes in the
>> > North
>> > >> >>Atlantic ocean circulation, are supported by the observations. This
>> > >> >>explains why, for example, European temperature variations are
>> > >> somewhat
>> > >> >>larger than those in other regions not effected so strongly by such
>> > >> climate
>> > >> >>processes.
>> > >> >>
>> > >> >>Other recent perspectives, by Ray Bradley and myself provide a far
>> > >> more
>> > >> >>balanced and nuanced (and less dogmatic or defensive) viewpoint.
>> > I'm
>> > >> not
>> > >> >>sure a written response to Broecker is worthwhile (this is,
>> > afterall,
>> > >> a
>> > >> >>"perspective" and everyone understands that a scientist may have a
>> > >> flawed
>> > >> >>perspective). If Wally wants this to be his legacy, so be it...
>> > >> >>
>> > >> >>Phil and others have a review article coming out in the near future
>> > >> which
>> > >> >>also provides a much more balanced perspective on the climate
>> > changes
>> > >> of
>> > >> >>the past millennium, and will set the record straight once again
>> > (good
>> > >> >>timing Phil!). Science's embargo policy prevents me from saying
>> > much
>> > >> more
>> > >> >>at this time, but if Phil or anyone else wishes to comment further,
>> > >> I'd
>> > >> >>encourage it.
>> > >> >>
>> > >> >>Well, I've still got some snow to shovel here in Charlottesville!
>> > >> Happy
>> > >> >>weekend to all,
>> > >> >>
>> > >> >>mike
>> > >> >>
>> > >> >>p.s. For those with electronic subscriptions, Broecker's latest
>> > piece
>> > >> can
>> > >> >>be found here:
>> > >> >>
>> > >> >> PALEOCLIMATE:
>> > >> >>        Was the Medieval Warm Period Global?
>> > >> >>        Wallace S. Broecker
>> > >> >>        Science Feb 23 2001: 1497-1499. [Summary] [Full Text]
>> > >> >>
>> > >> >>http://www.sciencemag.org/cgi/content/full/291/5508/1497
>> > >> >>
>> > >> >>While my previous perspective piece is here:
>> > >> >>   CLIMATE CHANGE:
>> > >> >>   Lessons for a New Millennium
>> > >> >>   Michael E. Mann
>> > >> >>   Science 2000 July 14; 289: 253-254. (in Perspectives) [Summary]
>> > >> [Full
>> > >> >>Text]
>> > >> >>URL:
>> > >>
>> > >>http://www.sciencemag.org/cgi/content/full/289/5477/253?maxtoshow=&HIT 
>> S=10&h
>> > >>
>> > >>its=10&RESULTFORMAT=&author1=Mann&searchid=QID_NOT_SET&stored_search=& 
>> FIRSTI
>> > >> >>NDEX=&fdate=10/1/1995&tdate=2/28/2001
>> > >> >>
>> > >> >>and Bradley's is here:
>> > >> >>
>> > >> >>   PALEOCLIMATE: Enhanced: 1000 Years of Climate Change
>> > >> >>   Ray Bradley
>> > >> >>   Science 2000 May 26; 288: 1353-1355. (in Perspectives) [Summary]
>> > >> [Full
>> > >> >>Text]
>> > >> >>
>> > >> >>URL:
>> > >>
>> > >>http://www.sciencemag.org/cgi/content/full/288/5470/1353?maxtoshow=&HI 
>> TS=10&
>> > >>
>> > >>hits=10&RESULTFORMAT=&author1=Bradley&searchid=QID_NOT_SET&stored_sear 
>> ch=&FI
>> > >> >>RSTINDEX=&fdate=10/1/1995&tdate=2/28/2001
>> > >> >>
>> > >> >>>Dear Michael--The third point below has comments on the
>> > controversy
>> > >> >>>betweenyou and Broecker--I'd be interested in your response (did
>> > >> Wally not
>> > >> >>>just understand what your data show?).
>> > >> >>>
>> > >> >>>Mike
>> > >> >>>
>> > >> >>>Three Wojick Pieces on Climate Change.
>> > >> >>>I've been busy busy.
>> > >> >>>
>> > >> >>>David
>> > >> >>>
>> > >> >>>FIRST, the latest issue of Insight Magazine includes a
>> > >> point-counterpoint
>> > >> >>>between measly old me and the great Robert Watson. Boy has he got
>> > >> >>>credentials! Too bad he's wrong.
>> > >> >>>
>> > >> >>><http://www.insightmag.com/archive/200103143.shtml>
>> > >> >>>
>> > >> >>>Symposium: Do scientists have compelling evidence of global
>> > warming?
>> > >> >>>
>> > >> >>>Yes: Rising sea levels worldwide and retreating Arctic glaciers
>> > are
>> > >> ominous
>> > >> >>>signs.
>> > >> >>>
>> > >> >>>By Robert T. Watson -- chairman of the UN Intergovernmental Panel
>> > on
>> > >> >>>Climate Change, chief scientist at the World Bank and former chief
>> > >> science
>> > >> >>>advisor to the Clinton White House.
>> > >> >>>
>> > >> >>>No: Despite the overheated rhetoric, there is no new evidence of
>> > >> warming
>> > >> >>>
>> > >> >>>By David E. Wojick -- covers climate policy for Electricity Daily
>> > and
>> > >> is a
>> > >> >>>science adviser to the Greening Earth Society
>> > >> >>><http://www.greeningearthsociety.org>, as well as Undereditor of
>> > the
>> > >> >>>Washington Pest <http://www.WashingtonPest.com>
>> > >> >>>
>> > >> >>>SECOND, the February 15 Eco-logic on-line has published "The Black
>> > >> Hole of
>> > >> >>>Global Climate Government" by David Wojick, my detailed attack on
>> > the
>> > >> >>>Framework Convention on Climate Change. It includes a lot of the
>> > >> actual
>> > >> >>>treaty language.
>> > >> >>>
>> > >> >>><http://www.eco.freedom.org/el/20010202/wojick.shtml>
>> > >> >>>
>> > >> >>>THIRD, here is a draft Electricity Daily article of mine. Seems
>> > I'm
>> > >> not the
>> > >> >>>only one who thinks the IPCC is nuts.
>> > >> >>>
>> > >> >>>Climate Guru Kicks The Hockey Stick
>> > >> >>>by David Wojick (dwojick@shentel.net)
>> > >> >>>
>> > >> >>>Global warming is natural and the recent warming is probably no
>> > >> exception.
>> > >> >>>This is the controversial argument made by prominent climatologist
>> > >> Wallace
>> > >> >>>S. Broecker in today's issue of Science.
>> > >> >>>
>> > >> >>>Broecker's bombshell bears the seemingly innocent title "Was the
>> > >> Medieval
>> > >> >>>Warm Period Global?" It may seem esoteric, but whether the
>> > apparent
>> > >> warmth
>> > >> >>>reported in Europe about 1000 years ago was global or simply local
>> > is
>> > >> >>>becoming a central issue in climate science. What makes it
>> > >> contentious is
>> > >> >>>the recent claims by the United Nations Intergovernmental Panel on
>> > >> Climate
>> > >> >>>Change that the earth is warmer now than it has been for
>> > millennia,
>> > >> and
>> > >> >>>that therefore human carbon dioxide emissions are to blame.
>> > Broecker,
>> > >> a
>> > >> >>>leading figure at Lamont-Doherty Earth Observatory, Columbia
>> > >> University,
>> > >> >>>questions both IPCC claims.
>> > >> >>>
>> > >> >>>The focus of the debate is a 1000-year temperature reconstruction
>> > >> known in
>> > >> >>>climate circles as the "hockey stick". Produced in 1999 by M. E.
>> > >> Mann, R.
>> > >> >>>S. Bradley, M. K. Hughes, the long handle of the hockey stick
>> > shows
>> > >> global
>> > >> >>>temperatures for the first 8 centuries as basically unchanging,
>> > >> followed by
>> > >> >>>the sharply up-tilting blade of the last 150 years or so. The Mann
>> > et
>> > >> al
>> > >> >>>hockey stick is the central feature of the recently released IPCC
>> > >> working
>> > >> >>>group one Summary for Policy makers, which claims to embody the
>> > best
>> > >> of
>> > >> >>>climate science.
>> > >> >>>
>> > >> >>>Broecker does not like the hockey stick, nor the conclusions the
>> > IPCC
>> > >> draws
>> > >> >>>from it. He says " A recent, widely cited reconstruction (Mann's)
>> > >> leaves
>> > >> >>>the impression that the 20th century warming was unique during the
>> > >> last
>> > >> >>>millennium. It shows no hint of the Medieval Warm Period (from
>> > around
>> > >> 800
>> > >> >>>to 1200 A.D.) during which the Vikings colonized Greenland,
>> > >> suggesting that
>> > >> >>>this warm event was regional rather than global. It also remains
>> > >> unclear
>> > >> >>>why just at the dawn of the Industrial Revolution and before the
>> > >> emission
>> > >> >>>of substantial amounts of anthropogenic greenhouse gases, Earth's
>> > >> >>>temperature began to rise steeply. Was it a coincidence? I do not
>> > >> think so.
>> > >> >>>Rather, I suspect that the post-1860 natural warming was the most
>> > >> recent in
>> > >> >>>a series of similar warmings spaced at roughly 1500-year intervals
>> > >> >>>throughout the present inter-glacial, the Holocene."
>> > >> >>>
>> > >> >>>Broecker presents the evidence for a global Medieval Warm Period,
>> > as
>> > >> well
>> > >> >>>as for a Little Ice Age from around 1300 to 1860, when the present
>> > >> >>>temperature rise begins. He also argues that the "proxy" evidence
>> > >> used by
>> > >> >>>Mann et al, such as tree ring data, is ill suited to the time
>> > period
>> > >> and
>> > >> >>>temperature variation -- less than one degree C -- in question.
>> > >> >>>
>> > >> >>>As he puts it, "In my estimation, at least for time scales greater
>> > >> than a
>> > >> >>>century or two, only two proxies can yield temperatures that are
>> > >> accurate
>> > >> >>>to 0.5 C: the reconstruction of temperatures from the elevation of
>> > >> mountain
>> > >> >>>snowlines and borehole thermometry. Tree ring records are useful
>> > for
>> > >> >>>measuring temperature fluctuations over short time periods but
>> > cannot
>> > >> pick
>> > >> >>>up long-term trends because there is no way to establish the
>> > >> long-term
>> > >> >>>evolution in ring thickness were temperatures to have remained
>> > >> constant."
>> > >> >>>
>> > >> >>>Broecker acknowledges that the proxy evidence is necessarily
>> > somewhat
>> > >> >>>"murky", but his conclusion is that "climatic conditions have
>> > >> oscillated
>> > >> >>>steadily over the past 100,000 years, with an average period close
>> > to
>> > >> 1500
>> > >> >>>years... The swing from the Medieval Warm Period to the Little Ice
>> > >> Age was
>> > >> >>>the penultimate of these oscillations." The implication being that
>> > >> some, if
>> > >> >>>not all, of the present warming is the natural swing out of the
>> > >> Little Ice
>> > >> >>>Age, and that Mann et al, as well as the IPCC, are mistaken.
>> > >> >>>
>> > >> >>>
>> > >> >>>--
>> > >> >>>
>> > >> >>>
>> > >> >>>Dr. David E. Wojick
>> > >> >>>President
>> > >> >>>Climatechangedebate.org
>> > >> >>>Subscribe to the free debate listserv at
>> > >> http://www.climatechangedebate.org
>> > >> >>>Non subscribers can follow the debate at
>> > >> >>>http://www.eScribe.com/science/ClimateChangeDebate/
>> > >> >>>
>> > >> >>>
>> > >> >>>
>> > >> >>>
>> > >>
>> > >>_______________________________________________________________________
>> > >> >>                     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
>> > >> >>       http://www.evsc.virginia.edu/faculty/people/mann.html
>> > >> >
>> > >> >
>> > >> >
>> > >> >
>> > >> >Thomas J.  Crowley
>> > >> >Dept. of Oceanography
>> > >> >Texas A&M University
>> > >> >College Station, TX  77843-3146
>> > >> >979-845-0795
>> > >> >979-847-8879 (fax)
>> > >> >979-845-6331 (alternate fax)
>> > >> >
>> > >> >
>> > >> >
>> > >> >
>> > >>
>> > _______________________________________________________________________
>> > >>                     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
>> > >>          http://www.evsc.virginia.edu/faculty/people/mann.html
>> >
>> > >>
>> > >>
>> > >>
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > _______________________________________________________________________
>> >                     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
>> >          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 
>---------------------------------------------------------------------------
-
     
>
>
>
_______________________________________________________________________
                     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
       http://www.evsc.virginia.edu/faculty/people/mann.html


