Re: [Phys-l] Still More Global Warming

[Jim Diamond <jimd@linfield.edu>]

"Daryl L Taylor" <Daryl@DarylScience.com>wrote:

> Date: Mon, 20 Aug 2007 15:18:10 -0400
> From: "Daryl L Taylor" <Daryl@DarylScience.com>
> Subject: Re: [Phys-l] Still More Global Warming

> ... In fact, according to
> Dansgaard-Oeschger, these cycles persist regardless of the CO2 levels and we
> are currently about 150 years INTO a 'moderate' Modern Warming period that
> they expect to last for the next few centuries; equaling the Medieval
> Climate Optimum of 900-1300 AD where the average global temp was 2-3 degrees
> C warmer than now with how much man-made CO2 in the atmosphere? 
>
> All in all, if anyone would bother to look at the data,...
>   
There are so many problems in this post, it is difficult to know where 
to begin. This poster should read much more about DO oscillations, for 
starters. This author does not seem to be aware of the National Academy 
of Sciences study, Surface Temperature Reconstructions for the Last 
2,000 Years; it is available free from the NAS here 
<http://www.nap.edu/catalog/11676.html> .

Here are the principle conclusions reported in the study:

   After considering all of the available evidence, including the
   curves shown in
   Figure S-1 [see the page numbered as page 2, the 17th page in the
   PDF - JD]
   the committee has reached the following conclusions:
   • The instrumentally measured warming of about 0.6°C during the 20th
   century
   is also reflected in borehole temperature measurements, the retreat
   of glaciers, and
   other observational evidence, and can be simulated with climate models.
   • Large-scale surface temperature reconstructions yield a generally
   consistent pic-
   ture of temperature trends during the preceding millennium,
   including relatively warm
   conditions centered around A.D. 1000 (identified by some as the
   “Medieval Warm
   Period”) and a relatively cold period (or “Little Ice Age”) centered
   around 1700. The
   existence of a Little Ice Age from roughly 1500 to 1850 is supported
   by a wide variety
   of evidence including ice cores, tree rings, borehole temperatures,
   glacier length records,
   and historical documents. Evidence for regional warmth during
   medieval times can be
   found in a diverse but more limited set of records including ice
   cores, tree rings, marine
   sediments, and historical sources from Europe and Asia, but the
   exact timing and
   duration of warm periods may have varied from region to region, and
   the magnitude
   and geographic extent of the warmth are uncertain.
   • It can be said with a high level of confidence that global mean
   surface tempera-
   ture was higher during the last few decades of the 20th century than
   during any
   comparable period during the preceding four centuries. This
   statement is justified by
   the consistency of the evidence from a wide variety of
   geographically diverse proxies.
   • Less confidence can be placed in large-scale surface temperature
   reconstructions
   for the period from A.D. 900 to 1600. Presently available proxy
   evidence indicates that
   temperatures at many, but not all, individual locations were higher
   during the past 25
   years than during any period of comparable length since A.D. 900.
   The uncertainties
   associated with reconstructing hemispheric mean or global mean
   temperatures from
   these data increase substantially backward in time through this
   period and are not yet
   fully quantified.
   • Very little confidence can be assigned to statements concerning
   the hemispheric
   mean or global mean surface temperature prior to about A.D. 900
   because of sparse
   data coverage and because the uncertainties associated with proxy
   data and the methods
   used to analyze and combine them are larger than during more recent
   time periods.


To me, these conclusions seem to me to be in direct opposition to the 
claims of the author of this post. I find this particular conclusion 
especially disturbing:

   It can be said with a high level of confidence that global mean
   surface tempera-
   ture was higher during the last few decades of the 20th century than
   during any
   comparable period during the preceding four centuries.

For more comment on this issue, especially the work of Mann et al., see, 
for example, this excerpt from the entry in RealClimate 
<http://www.realclimate.org/index.php?p=33>:

   As noted by Jones and Mann (2004) [Jones, P.D., Mann, M.E., Climate
   Over Past Millennia
   <http://iri.columbia.edu/%7Egoddard/EESC_W4400/CC/jones_mann_2004.pdf>,
   /Reviews of Geophysics/, 42, RG2002, doi: 10.1029/2003RG000143,
   2004], arguments that such evidence supports anomalous global warmth
   during this time period is based on faulty logic and/or
   misinterpretations of the available evidence.

Regards,
Jim

--
James J. Diamond, Jr., Ph.D.,
Professor of Chemistry, Chemistry Department,
Linfield College, 900 S.E. Baker St. McMinnville, OR 97128
Voice:503.883.2471      Fax: 503.883.2538 jimd@linfield.edu