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

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. I t*. Concept: surface temperature

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

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  1. 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

  2. I t* Concept: surface temperature histories have distinctive borehole temperature signatures. Snapshot at t*

  3. 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)

  4. 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 > 1 °C 4. Variability Mann et al. [2009], Science, 326.

  5. 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

  6. Regions having multiple boreholes with depth > 600m

  7. N = 45

  8. N = 12

  9. N = 45

  10. N = 5 Problems: Small sample Suspicious profiles Lack of thermal conductivity info.

  11. Chapman & Davis Eos, Sept 14, 2010

  12. 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 (> 600 m) boreholes with thermal conductivity information needed. • If geog. variability real, less reliance on stacking.

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