Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] Still More Global Warming



Hi, Jim. I'll be checking the source you cite in much more detail as I find
the time. However, my first impression is that you are basing your rebuttal
to my response to JMGreen's post on one, and only one, source; a book
written for the US Congress. However, most telling is a statement in their
own overview;

"In response to a request from Congress...assesses the state of scientific
efforts to reconstruct surface temperature records for Earth during
approximately the last 2,000 years and the implications of these efforts..."


By skimming the chapter contents, it seems this work is not much more than a
review of *some* of the temperature reconstructions in peer-reviewed
journals along with the BASC's own view on the scientific merits of that
research, usually quite negative. It seems this isn't much more than another
review of selected works that praises the ones they agree with and steps on
the ones they don't. However, I will take a closer look. Honest!

The only other comment I can muster right now, before delving into prep work
for the upcoming academic year, is your seeming contradiction of citing this
work and then relying on any work by Mann. This BASC work specifically
claims that any works that depend on proxy data cannot be reliable for one
reason or another. Mann's work not only depends on proxy data, but selective
proxy data dating back to 1000AD. However, not only has Mann's work been
discredited scientifically, it has been discredited mathematically and
historically. How can you rely on one work that spends so much time driving
home the point that proxy data is bad then rely on one that depends on it?

The BASC work:

" 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."


The 1st statement of the Mann work you cite is:

" We review evidence for climate change over the past
several millennia from instrumental and high-resolution
climate ‘‘proxy’’ data sources and climate modeling studies."


On the other hand, I do have to agree with one of your points;

" 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."

No argument. Four centuries ago was roughly 1600, eh? Medieval Warming
Period was roughly 900-1300AD, generally agreed to be a couple of degrees C
warmer than today. Little Ice Age was roughly 1300-1850AD. So, yep. Now that
the warm period of the Norse Greenlanders is 700 years ago, seems right
that a scientific source could assert that the last 20 or 30 or so years is
warmer than any other period of the last 400. However, again it seems to me
that the 'big picture' is being ignored. 400 years is nothing. Hell, I'm
pretty sure my 9th grade English Lit teacher was older than that...

-Daryl

This email sent using 100% certified recycled electrons.
-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Jim Diamond
Sent: Thursday, August 23, 2007 1:29 AM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] Still More Global Warming

"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

_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l