1. Michael E. Mann Department of Meteorology and Earth and Environmental Systems Institute (ESSI) Penn State University National Academy of Sciences March 3, 2006 Climate Over the Past 1-2 Millennia

2. INSTRUMENTAL TEMPERATURE RECORD GLOBAL PROXY CLIMATE RECORDS Annual Resolution Proxy Climate Indicators

4. Reconstructed Surface Temperatures Mann, M.E., Bradley, R.S., Hughes, M.K., Global-Scale Temperature Patterns and Climate Forcing Over the Past Six Centuries, Nature, 392, 779-787, 1998.

5. Reconstructed Surface Temperatures Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

6. Reconstructed Surface Temperatures Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

7. Jones, P.D., Mann, M.E., Climate Over Past Millennia, Reviews of Geophysics, 42, RG2002, doi:10.1029/2003RG000143, 2004. Reconstructed Surface Temperatures

8. Reconstructions of Northern Hemisphere mean temperatures for the last 1000 years and instrumental record (black line) From “Wikipedia”

9. Oerlemans, J., Extracting a climate signal from 169 Glacier Records, Science, March 3 (2005). From “Wikipedia” Oerlemans (2005) Glacier- based estimate

10. Natural 100012001400160018002000 Volcanism Solar CLIMATE FORCINGS Crowley, T.J., Causes of Climate Change Over the Past 1000 Years, Science, 289 270-277, 2000.

11. CLIMATE FORCINGS Anthropogenic Greenhouse Gases Industrial Aerosols Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

12. Jones, P.D., Mann, M.E., Climate Over Past Millennia, Reviews of Geophysics, 42, RG2002, doi:10.1029/2003RG000143, 2004. MODEL SIMULATIONS

13. Past CO 2 as an additional constraint? Gerber, S., Joos, F., Bruegger, P.P., Stocker, T.F. Mann, M.E., Sitch, S., Scholze, M., Constraining temperature variations over the last millennium by comparing simulated and observed atmospheric CO2, Climate Dynamics, in press (2002)

14. Model forced by long- term natural and anthropogenic radiative forcing Sensitivity varied from 1.5 to 4.5 o C/2xCO 2 (orange shading) Esper et al recon. well outside range… Mann et al Bern “CC” Climate Model Past CO 2 as an additional constraint?

15. Gerber, S., Joos, F., Bruegger, P.P., Stocker, T.F. Mann, M.E., Sitch, S., Scholze, M., Constraining temperature variations over the last millennium by comparing simulated and observed atmospheric CO2, Climate Dynamics,, 20, 281-299, 2003. Mann et al Past CO 2 as an additional constraint? Bern “CC” (coupled Climate Carbon cycle) model includes Lund-Potsdam-Jena Dynamic Global Vegetation Model w/ Impulse Response Representation of Ocean Dynamics Allows prediction of natural variations in CO 2 as a response to large-scale surface temperature changes Bern “CC” Climate Model Model forced by long- term natural and anthropogenic radiative forcing Sensitivity varied from 1.5 to 4.5 o C/2xCO 2 (orange shading)

16. Mann et al Past CO 2 as an additional constraint? Bern “CC” Climate Model Natural CO 2 variations from Ice Cores consistent with the model predictions for the moderate sensitivities consistent w/ Mann et al reconstruction Gerber, S., Joos, F., Bruegger, P.P., Stocker, T.F. Mann, M.E., Sitch, S., Scholze, M., Constraining temperature variations over the last millennium by comparing simulated and observed atmospheric CO2, Climate Dynamics,, 20, 281-299, 2003.

17. Natural CO 2 variations from Ice Cores consistent with the model predictions for the moderate sensitivities consistent w/ Mann et al reconstruction Larger temperature variations (e.g., greater sensitivity of temperature to solar variability) is inconsistent with comparison of modeled and observed CO 2 Past CO 2 as an additional constraint?

18. Reconstructed Surface Temperatures Mann, M.E., Bradley, R.S., Hughes, M.K., GRL, ‘99

23. ROBUSTNESS OF THE MANN, BRADLEY, HUGHES RECONSTRUCTION OF NORTHERN HEMISPHERE SURFACE TEMPERATURES: EXAMINATION OF CRITICISMS BASED ON THE NATURE AND PROCESSING OF PROXY CLIMATE EVIDENCE EUGENE R. WAHL 1 and CASPAR M. AMMANN 2 1 Environmental Studies and Geology Division, Alfred University, Alfred, New York, U.S.A. One Saxon Dr., Alfred, NY 14802 wahle@alfred.edu 607.871.2604 607.871.2697 (fax) 2 National Center for Atmospheric Research[1], Boulder, Colorado, U.S.A.[1] The authors contributed equally to the development of the research presented. (Climatic Change, in press) Abstract. The Mann et al. (1998) Northern Hemisphere annual temperature reconstruction over 1400-1980 is examined in light of recent criticisms concerning the nature and processing of included climate proxy data. A systematic sequence of analyses is presented that examine issues concerning the proxy evidence, utilizing both indirect analyses via exclusion of proxies and processing steps subject to criticism, and direct analyses of principal component (PC) processing methods in question. Altogether new reconstructions over 1400-1980 are developed in both the indirect and direct analyses, which demonstrate that the Mann et al. reconstruction is robust against the proxy-based criticisms addressed. In particular, reconstructed hemispheric temperatures are demonstrated to be largely unaffected by the use or non-use of PCs to summarize proxy evidence from the data-rich North American region. When proxy PCs are employed, neither the time period used to "center" the data before PC calculation nor the way the PC calculations are performed significantly affects the results, as long as the full extent of the climate information actually in the proxy data is represented by the PC time series. Clear convergence of the resulting climate reconstructions is a strong indicator for achieving this criterion. Also, recent "corrections" to the Mann et al. reconstruction that suggest 15th century temperatures could have been as high as those of the late-20th century are shown to be without statistical and climatological merit. Our examination does suggest that a slight modification to the original Mann et al. reconstruction is justifiable for the first half of the 15th century (~ +0.05°), which leaves entirely unaltered the primary conclusion of Mann et al. (as well as many other reconstructions) that both the 20th century upward trend and high late-20th century hemispheric surface temperatures are anomalous over at least the last 600 years. Our results are also used to evaluate the separate criticism of reduced amplitude in the Mann et al. reconstructions over significant portions of 1400-1900, in relation to some other climate reconstructions and model-based examinations. We find that, from the perspective of the proxy data themselves, such losses probably exist, but they may be smaller than those reported in other recent work.

24. MBH98 readily reproduced in independent analysis, when the full data set and correct method are folllowed.

25. Putative reconstruction indicating anomalous 15 th century warmth results from censoring of key tree-ring data, and not any purported ‘errors’ in MBH98.

26. This reconstruction dramatically fails verification.

27. The MBH98 Reconstruction is largely insensitive to whether PCA is used to represent tree-ring networks.

28. The MBH98 Reconstruction is largely insensitive to the centering convention used in PCA to represent tree-ring networks, as long as standard selection rules are followed.

29. Putative anomalous 15 th century warmth follows from exclusion of key data. The resulting reconstructions fail verification.

30. Failure to reject reconstructions which fail statistical verification also invalidates conclusions of Von Storch et al (2004) and Burger and Cubasch (2005). Putative anomalous 15 th century warmth follows from exclusion of key data. The resulting reconstructions fail verification.

31. RegEM Approach vs MBH98 PCA approach “CFR” approaches Rutherford, S., Mann, M.E., Osborn, T.J., Bradley, R.S., Briffa, K.R., Hughes, M.K., Jones, P.D., Proxy- based Northern Hemisphere Surface Temperature Reconstructions: Sensitivity to Methodology, Predictor network, Journal of Climate, 18, 2308-2329, 2005.

32. RegEm Approach vs MBH98 PCA approach Rutherford, S., Mann, M.E., Osborn, T.J., Bradley, R.S., Briffa, K.R., Hughes, M.K., Jones, P.D., Proxy- based Northern Hemisphere Surface Temperature Reconstructions: Sensitivity to Methodology, Predictor network, Journal of Climate, 18, 2308-2329, 2005. “CFR” approaches

35. Jones, P.D., Mann, M.E., Climate Over Past Millennia, Reviews of Geophysics, 42, RG2002, doi:10.1029/2003RG000143, 2004. Reconstructed Surface Temperatures

36. composite of 8 NH proxy series (Mann and Jones ’03) Composite of 7 NH proxy series (North American PC#1 tree-ring series eliminated) Instrumental NH Series

37. RegEm Approach vs MBH98 PCA approach “CFR” approaches Rutherford, S., Mann, M.E., Osborn, T.J., Bradley, R.S., Briffa, K.R., Hughes, M.K., Jones, P.D., Proxy- based Northern Hemisphere Surface Temperature Reconstructions: Sensitivity to Methodology, Predictor network, Journal of Climate, 18, 2308-2329, 2005.

38. Geophysical Research Letters, 29 (10), 1501, doi: 10.1029/2001GL014554, 2002.

39. 1877

40. Geophysical Research Letters, 29 (10), 1501, doi: 10.1029/2001GL014554, 2002.

41. Journal of Climate, 16, 462-479, 2003 85% missing 95% missing

42. Journal of Climate, 16, 462-479, 2003 85% missing 95% missing

43. Pseudo-Proxy Model Reconstruction von Storch et al. 2004 poor calibration and verification MBH98 and other CFR Methods guards against this! Burger and Cubasch (2005) suffers from same problem.

44. “CFR” approach Mann, M.E., Rutherford, S., Wahl, E., Ammann, C., Testing the Fidelity of Methods Used in Proxy-based Reconstructions of Past Climate, Journal of Climate, 18, 4097-4107, 2005.

45. “CFR” approach Mann, M.E., Rutherford, S., Wahl, E., Ammann, C., Testing the Fidelity of Methods Used in Proxy-based Reconstructions of Past Climate, Journal of Climate, 18, 4097-4107, 2005. “CFR” approach

46. 100012001400160018002000 Volcanism Solar Crowley, T.J., Causes of Climate Change Over the Past 1000 Years, Science, 289 270-277, 2000. “Maunder Minimum” Influence of Natural Radiative Forcing

47. LIA winter cooling in Europe associated with an NAO trend due to solar irradiance changes, interacting w/ stratospheric atmospheric dynamics and chemistry Empirical NASA/GISS Model European Winter Cooling During the Little Ice Age Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind, D., Waple, A., Solar forcing of regional climate change during the Maunder Minimum, Science, 294, 2149- 2152, 2001.

48. Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and Solar forcing of Climate Change During the Pre-Industrial era, Journal of Climate, 16, 4094-4107, 2003. Volcanic Radiative Summer Cooling Ensemble average summer (Jun-Aug) surface temperature response following eruption of Pinatubo.

49. Volcanic Winter Dynamical Warming Ensemble average winter (Dec-Feb) surface temperature response following eruption of Pinatubo. Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and Solar forcing of Climate Change During the Pre-Industrial era, Journal of Climate, 16, 4094-4107, 2003.

50. Esper, J., Cook, E.R., Schweingruber, F.H., Low- Frequency Signals in Long Tree-Ring Chronologies for Reconstructing Past Temperature Variability, Science, 295, 2250-2253, 2002. Mid-Latitude Summers Greater variability?

51. Mid-Latitude Summers 100012001400160018002000 Greater variability?

52. Proxy based reconstruction GCM Solar + Volcanic patterns Annual average late 17th vs late 18th Century Temperature change Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and Solar forcing of Climate Change During the Pre-Industrial era, Journal of Climate, 16, 4094- 4107, 2003.

53. 1998 Global Temperature Pattern

54. Cane, M.A., A.C. Clement, A. Kaplan, Y. Kushnir, D. Pozdnyakov, R. Seager, S.E. Zebiak, and R. Murtugudde, Twentieth-Century Sea Surface Temperature Trends, Science, 275, 957-960, 1997. Theoretical mechanism for natural radiative forcing of El Nino

55. Composite Nino3 (100 realizations of CZ model) Theoretical mechanism for natural radiative forcing of El Nino Tropical Volcanic radiative forcing (0.1 x W/m 2 )

56. Composite Nino3 (100 realizations of CZ model) Theoretical mechanism for natural radiative forcing of El Nino Response to Volcanic Forcing Tropical Volcanic radiative forcing (0.1 x W/m 2 ) Mann, M.E., Cane, M.A., Zebiak, S.E., Clement, A., Volcanic and Solar Forcing of The Tropical Pacific Over the Past 1000 Years, Journal of Climate, 18, 447-456, 2005.

57. Tropical volcanic radiative forcing (0.1 x W/m2) Theoretical mechanism for natural radiative forcing of El Nino Superposed Epoch Analysis AD 1649-1868 all (7) tropical events exceeding -2 W/m2 Superposed Epoch Analysis AD 1000-1999 All (7) tropical events exceeding -4 W/m2 Mann, M.E., Cane, M.A., Zebiak, S.E., Clement, A., Volcanic and Solar Forcing of the Tropical Pacific Over the Past 1000 Years, Journal of Climate, 18, 447-456, 2005.

58. Tropical volcanic radiative forcing (0.1 x W/m2) Composite Nino3 (100 realizations of CZ model) Theoretical mechanism for natural radiative forcing of El Nino 40 year smooth Tropical Solar radiative forcing (W/m 2 )

59. Composite Nino3 (100 realizations of CZ model) Theoretical mechanism for natural radiative forcing of El Nino Response to Solar Forcing 40 year smooth Tropical Solar radiative forcing (W/m 2 ) (40 year smooth) Mann, M.E., Cane, M.A., Zebiak, S.E., Clement, A., Volcanic and Solar Forcing of the Tropical Pacific Over the Past 1000 Years, Journal of Climate, 18, 447-456, 2005.

60. Theoretical mechanism for natural radiative forcing of El Nino Combined response to Solar +Volcanic Forcing Ensemble mean Nino3 (100 realizations of CZ model) 40 year smooth Palymra coral isotopes (standardized to have same mean and standard deviation as Nino3 composite series) Mann, M.E., Cane, M.A., Zebiak, S.E., Clement, A., Volcanic and Solar Forcing of the Tropical Pacific Over the Past 1000 Years, Journal of Climate, 18, 447-456, 2005.

61. El Nino and North American Drought

62. El Nino vs. North American Drought over the Past Century Increased Drought La Nina El Nino Less Drought Courtesy of E.Cook

63. Linear correlation coefficient (r) is not a viable measure of statistical reconstructio n skill