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Science Forum Index » Environment Forum » On the Use of Borehole Temperatures to Deduce Earth's Climat
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| Dr. Convection |
 Posted: Sat Dec 20, 2003 10:16 pm |
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From:
http://www.co2science.org/journal/2003/v6n51c1.htm
On the Use of Borehole Temperatures to Deduce Earth's Climatic History
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Reference
Gonzalez-Rouco, F., von Storch, H. and Zorita, E. 2003. Deep soil
temperature as proxy for surface air-temperature in a coupled model
simulation of the last thousand years. Geophysical Research Letters 30:
10.1029/2003GL018264.
Background
In the words of the authors, "borehole temperature profiles (Huang et al.,
2000) are perhaps the only direct measurements of past temperatures, in
contrast to the analysis of other climate proxies that have to be
interpreted in terms of climate anomalies through transfer functions."
However, as they note, "the validity of the interpretation of borehole
temperature profiles has been questioned (Mann and Schmidt, 2003)."
What was done
Gonzalez-Rouco et al. investigated the relationship between simulated
surface air temperature (SAT) and terrestrial deep soil temperature (TDST)
in a climate simulation of the last millennium with the state-of-the-art
coupled climate model (ECHO-G) described by Legutke and Voss (1999), which
was driven by historical forcing provided by "solar variability, atmospheric
greenhouse gas concentrations, and radiative effects of stratospheric
volcanic aerosols, in the period 1000-1990 AD, derived from the estimations
provided by Crowley (2000)."
What was learned
The authors report finding that "at long timescales, annual TDST is a good
proxy for annual SAT, and their variations are almost indistinguishable from
each other" in a significant rebuff to the challenge of Mann and Schmidt
(2003). Also in contradiction of the many Mann-inspired claims that late
20th century warming has led to temperatures that are unprecedented over the
past millennium, they report that "the simulated annual global SAT shows a
period of temperatures roughly as warm as today around 1100 A.D. (the
Medieval Optimum), a subsequent cooling trend until around 1850 A.D. (the
Little Ice Age) punctuated by deeper temperature minima at around 1450 A.D.,
1700 A.D., and 1820 A.D., coincidental with known minima of the solar output
or periods of more frequent volcanic eruptions (the Spoerer, Maunder and
Dalton minima, respectively)." In addition, they note that "recent
reconstructions on extratropical tree-ring chronologies [such as Esper et
al. (2002), see our Editorial of 27 Mar 2002] indicate a better agreement
with the borehole based reconstructions."
What it means
As more and more data are collected and careful analyses are conducted, it
is becoming ever more clear that (1) there has been nothing unusual about
the temperature history of the past quarter-century and (2) current
temperatures do not materially exceed those of the Medieval Warm Period. If
the warming of the past hundred or so years has seemed unusually steep, it
is simply because the Little Ice Age was so cold, thanks largely to
historical variations in solar activity.
References
Crowley, T.J. 2000. Causes of climate change over the last 1000 years.
Science 289: 270-277.
Esper, J., Cook, E.R. and Schweingruber, F.H. 2002. Low-frequency signals
in long tree-ring chronologies for reconstructing past temperature
variability. Science 295: 2250-2253.
Huang, S., Pollack, H.N. and Shen, P.-Y. 2000. Temperature trends over the
past five centuries reconstructed from borehole temperatures. Nature 403:
756-758.
Legutke, S. and Voss, R. 1999. The Hamburg Atmosphere-Ocean Coupled
Circulation Model ECHO-G. Technical Report No. 18. German Climate
Computing Center, Hamburg, Germany.
Mann, M.E. and Schmidt, G.A. 2003. Ground vs. surface air temperature
trends: Implications for borehole surface temperature reconstructions.
Geophysical Research Letters 30: 10.1029/2003GL017170.
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Reviewed 17 December 2003
Center for the Study of Carbon Dioxide and Global Change
(www.co2science.org). |
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| Guest |
| Posted: Sun Dec 21, 2003 2:45 pm |
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In sci.environment Dr. Convection <Convection@convection.net> wrote:
Quote: http://www.co2science.org/journal/2003/v6n51c1.htm
In the words of the authors, "borehole temperature profiles (Huang et al.,
2000) are perhaps the only direct measurements of past temperatures, in
Well thats a very poor start, because of course they aren't.
Quote: However, as they note, "the validity of the interpretation of borehole
temperature profiles has been questioned (Mann and Schmidt, 2003)."
What was done
Gonzalez-Rouco et al. investigated the relationship between simulated
surface air temperature (SAT) and terrestrial deep soil temperature (TDST)
in a climate simulation of the last millennium with the state-of-the-art
coupled climate model (ECHO-G) described by Legutke and Voss (1999),
this too appears to be wrong, since
http://www.mad.zmaw.de/Klimamodelle/UbersichtvorgModelle/ECHO-G.html
says that ECHO-G uses
"The model uses annual mean corrections of heat and freshwater
fluxes at low and mid latidues"
Quote: which
was driven by historical forcing provided by "solar variability, atmospheric
greenhouse gas concentrations, and radiative effects of stratospheric
volcanic aerosols, in the period 1000-1990 AD, derived from the estimations
provided by Crowley (2000)."
What was learned
The authors report finding that "at long timescales, annual TDST is a good
proxy for annual SAT, and their variations are almost indistinguishable from
each other" in a significant rebuff to the challenge of Mann and Schmidt
(2003).
Thats true, if reported correctly.
Quote: Also in contradiction of the many Mann-inspired claims that late
20th century warming has led to temperatures that are unprecedented over the
past millennium, they report that "the simulated annual global SAT shows a
period of temperatures roughly as warm as today around 1100 A.D. (the
Medieval Optimum),
Given the forcing (presumably erik-1 from
http://chubasco.fis.ucm.es/~fi/for_wpa01/for_wpa01.html)
this looks somewhat unlikey. More likely an artefact of too-little
spin down from modern conditions. Which is presumably why erik-2 is
running.
-W
--
William M Connolley | wmc@bas.ac.uk | http://www.antarctica.ac.uk/met/wmc/
Climate Modeller, British Antarctic Survey | Disclaimer: I speak for myself
I'm a .signature virus! copy me into your .signature file & help me spread! |
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