Surface Temperature Anomalies for the Medieval Warm Period, Little Ice Age, and 20th Century Warming Determined from Borehole Temperatures

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Surface Temperature Anomalies for the Medieval
Warm Period, Little Ice Age, and 20th Century
Warming Determined from Borehole Temperatures

• David S. Chapman, Robert N. Harris
• and Michael G. Davis

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I t
Concept surface temperature histories have
distinctive borehole temperature signatures.
Snapshot at t
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Medieval Climate Anomaly (MCA)
Background I
Mann et al. 2009, Global Signatures and
Dynamical Origins of the Little Ice Age and
Medieval Climate Anomaly, Science, 326, 1256
1260.
Little Ice Age (LIA)
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MCA LIA Temperature Difference in Proxy-based
Temperature Reconstruction
Background II 1. Temp differences
avoid zero problem 2. Mean difference
0.24 C 3. Local differences gt 1 C 4.
Variability
Mann et al. 2009, Science, 326.
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Temperature Anomaly (C)
Amplitude (oC) LIA MCA -0.5 0.5
LIA MCA -0.5 0.0
LIA MCA -0.5 0.25
LIA MCA -0.25 0.5
LIA MCA 0.0 0.5
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Regions having multiple boreholes with depth gt
600m
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N 45
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N 12
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N 45
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N 5
Problems Small sample Suspicious profiles Lack
of thermal conductivity info.
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Chapman Davis Eos, Sept 14, 2010
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Conclusions

• Borehole T(z) useful complement to multiproxy
  methods.
• MCA, LIA, and recent warming have distinctive
  signatures in borehole temperature profiles
  (shape, amplitude, depth extent).
• Four regions (NE N. America S. Africa Cent.
  Europe Cent. Asia) do not have borehole T(z)
  anomalies identifiable as MCA, LIA.
• Amplitudes no greater than suggested by Mann et
  al.
• MCA/LIA stronger seasonal rather than annual
  signal?
• Borehole temperature noise level too great.
• Extensive warm period prior to 1000 CE
  inconsistent with baseline temperature from
  borehole studies
• More deep (gt 600 m) boreholes with thermal
  conductivity information needed.
• If geog. variability real, less reliance on
  stacking.