Re: OT: getting rid of the medieval warm period
- From: z <gzuckier@xxxxxxxxxxxxxx>
- Date: Mon, 10 Sep 2007 13:04:15 -0700
On Sep 7, 9:36 am, Eeyore <rabbitsfriendsandrelati...@xxxxxxxxxxx>
wrote:
In a thread here some time back I mentioned a climate researcher who I'd heard
was approached with respect to 'getting rid of the medieval warm period' in
order to make the IPCC case for AGW more compelling.
At the time I didn't have a cite but I just found it again.
http://www.epw.senate.gov/hearing_statements.cfm?id=266543
Statement of Dr. David Deming
University of Oklahoma
College of Earth and Energy
Climate Change and the Media
Mr. Chairman, members of the Committee, and distinguished guests, thank you for
inviting me to testify today. I am a geologist and geophysicist. I have a
bachelor's degree in geology from Indiana University, and a Ph.D in geophysics
from the University of Utah. My field of specialization in geophysics is
temperature and heat flow. In recent years, I have turned my studies to the
history and philosophy of science. In 1995, I published a short paper in the
academic journal Science. In that study, I reviewed how borehole temperature
data recorded a warming of about one degree Celsius in North America over the
last 100 to 150 years. The week the article appeared, I was contacted by a
reporter for National Public Radio. He offered to interview me, but only if I
would state that the warming was due to human activity. When I refused to do so,
he hung up on me.
I had another interesting experience around the time my paper in Science was
published. I received an astonishing email from a major researcher in the area
of climate change. He said, "We have to get rid of the Medieval Warm Period."
The Medieval Warm Period (MWP) was a time of unusually warm weather that began
around 1000 AD and persisted until a cold period known as the "Little Ice Age"
took hold in the 14th century. Warmer climate brought a remarkable flowering of
prosperity, knowledge, and art to Europe during the High Middle Ages.
The existence of the MWP had been recognized in the scientific literature for
decades. But now it was a major embarrassment to those maintaining that the 20th
century warming was truly anomalous. It had to be "gotten rid of."
In 1769, Joseph Priestley warned that scientists overly attached to a favorite
hypothesis would not hesitate to "warp the whole course of nature." In 1999,
Michael Mann and his colleagues published a reconstruction of past temperature
in which the MWP simply vanished. This unique estimate became known as the
"hockey stick," because of the shape of the temperature graph.
Normally in science, when you have a novel result that appears to overturn
previous work, you have to demonstrate why the earlier work was wrong. But the
work of Mann and his colleagues was initially accepted uncritically, even though
it contradicted the results of more than 100 previous studies. Other researchers
have since reaffirmed that the Medieval Warm Period was both warm and global in
its extent.
There is an overwhelming bias today in the media regarding the issue of global
warming. In the past two years, this bias has bloomed into an irrational
hysteria. Every natural disaster that occurs is now linked with global warming,
no matter how tenuous or impossible the connection. As a result, the public has
become vastly misinformed on this and other environmental issues.
Earth's climate system is complex and poorly understood. But we do know that
throughout human history, warmer temperatures have been associated with more
stable climates and increased human health and prosperity. Colder temperatures
have been correlated with climatic instability, famine, and increased human
mortality.
The amount of climatic warming that has taken place in the past 150 years is
poorly constrained, and its cause--human or natural--is unknown. There is no
sound scientific basis for predicting future climate change with any degree of
certainty. If the climate does warm, it is likely to be beneficial to humanity
rather than harmful. In my opinion, it would be foolish to establish national
energy policy on the basis of misinformation and irrational hysteria.
It stands to reason that the same folks who think a shift of a couple
of hundredths of a degree in the US average temp should "invalidate"
the global average temp would think that "Warmer climate brought a
remarkable flowering of prosperity, knowledge, and art to Europe
during the High Middle Ages" must therefore dominate global
temperature. In fact, you might be surprised how little of the globe
is actually covered by the US or Europe.
With distance in time, records that actually show warming of different
regions at different times get telescoped together, from the vantage
point of 500-1000 years later, into one long medieval European summer;
when in fact there was a lot of variability between regions and times.
Greenland seems to have enjoyed a couple of warm peaks at the
beginning and end of the period but a cool spell around 1100, at the
same time Scandinavia enjoyed its warm period (Crowley, T.J. and T.
Lowery, 2000: How warm was the Medieval warm period? Ambio, 29,
51-54.). Thus the
suggestion that this asynchronicity may have helped motivate the
Vikings' travel.
Similarly, the "Little Ice Age" is basically a record of cold dry
winters in central Europe during the 17th century; but evidence for
large temperature changes in this period as synchronous phenomena over
larger areas of the globe is sorely lacking. A sediment record from
just south of Newfoundland indicates the opposite pattern; cold
medieval and warm 16th to 19th century upper ocean temperatures
(Keigwin, L.D. and R.S. Pickart, 1999: Slope water current over the
Laurentian Fan on Interannual to Millennial Time Scales. Science, 286,
520-523.), suggesting that the European temperature record of
1000-1900 is the effect of changes in ocean currents in the North
Atlantic on a centuries long scale (the North Atlantic Oscillation)
which warm one region only at the expense of cooling another. Not
anything you could use to explain a sudden attack of global warming.
In China, for another instance, where they kept good records of this
sort of thing, there doesn't seem to be any correlation with the
Medieval Warming and Little Ice Age periods; eastern China appears to
have been warm from the 9th to 13th centuries, but overall China was
actually cold in the 12th and 14th centuries (Wang, S.W. and D.Y.
Gong, 2000: Climate in China during the four special periods in
Holocene. Progress in Nature Science, 10(5), 379-386.; Wang, S.W., J.
Ye, D. Gong and J. Zhu, 1998: Construction of mean annual temperature
series for the last one hundred years in China, Quart. J. Appl. Met.,
9(4), 392-401; Wang, S.W., J. Ye and D. Gong, 1998: Climate in China
during the Little Ice Age. Quaternary Sciences, 1, 54-64)
Now, all this has been Northern Hemisphere up to now; when you cross
through the equatorial region (where little evidence of medieval
warming or little ice age is seen), into the southern hemisphere, the
records are much sketchier, but there continues to be no evidence for
any Medieval Warming or Little Ice Age at all, even as you leave the
equatorial regions into the upper latitudes, where these changes are
seen in the Northern Hemisphere. In fact, the evidence for summer mean
temps (Jones, P.D., K.R. Briffa, T.P., Barnett and S.F.B. Tett, 1998:
High-resolution palaeoclimatic records for the last millennium:
interpretation, integration and comparison with General Circulation
Model control run temperatures. The Holocene, 8, 455-471.) and annual
mean temps (Mann, M.E., E. Gille, R.S. Bradley, M.K. Hughes, J.T.
Overpeck, F.T. Keimig and W. Gross, 2000: Global temperature patterns
in past centuries: An interactive presentation. Earth Interactions,
4/4, 1-29.) suggest markedly different behaviour from the Northern
Hemisphere. Speleothem evidence (isotopic evidence from calcite
deposition in stalagmites and stalactites) from South Africa indicates
anomalously cold conditions only prior to the 19th century, while
speleothem and glacier evidence from the Southern Alps of New Zealand
suggest cold conditions during the mid-17th and mid-19th centuries
(Salinger, M.J., 1995: Southwest Pacific temperature: trends in
maximum and minimum temperatures. Atmos. Res., 37, 87-100.). But
dendroclimatic evidence from Tasmania (Cook, E.R., B.M. Buckley and
R.D. D'Arrigo, 2000: Warm-Season Temperatures since 1600 B.C.
Reconstructed from Tasmanian Tree Rings and Their Relationship to
Large-Scale Sea Surface Temperature Anomalies. Clim. Dyn., 16, 79-91.)
shows no evidence of unusual coldness at these times. More evidence
that the Medieval Warming and Little Ice Age were just localized North
Atlantic phenomena.
So, looking at the supposed Medieval Warming Period and Little Ice Age
averaged with the rest of the temps over the northern hemisphere damps
out the temperature swings quite a bit, and adding in the few from the
southern hemisphere for a global average damps them out even more.
Global average temp. instead of northern hemisphere average temp,
shows no real evidence of any unusual global warmth 1000-1400 or cold
1400-1900. The only real globally seen remarkable temperature change
in the past 1,000 years, seen with a lot of obvious similarity and
simultaneity in many regions all over the world, is the unprecedented
warming of the late 20th century. The sudden steep climb over the past
century is unmistakably global, the averaged temperature measured
directly over a large number of sites in all regions.
.
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- From: Eeyore
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