Climate of the Past www.clim-past.net 1814-9324 1814-9332 3 4 2007 10.5194/cp-3-591-2007 http://www.clim-past.net/3/591/2007/ http://www.clim-past.net/3/591/2007/cp-3-591-2007.html http://www.clim-past.net/3/591/2007/cp-3-591-2007.pdf 591 609 2007-10-05 Millennial temperature reconstruction intercomparison and evaluation M. N. Juckes m.n.juckes@rl.ac.uk M. R. Allen K. R. Briffa J. Esper G. C. Hegerl A. Moberg T. J. Osborn S. L. Weber British Atmospheric Data Centre, SSTD, Rutherford Appleton Laboratory Chilton, Didcot, Oxfordshire, OX11 0QX, UK University of Oxford, Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK Swiss Federal Research Institute WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland Div. of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Science, Duke University, Durham, NC, USA Department of Meteorology and Department of Physical Geography and Quaternary Geology, Stockholm University, 106 91 Stockholm, Sweden Royal Netherlands Meteorological Institute (KNMI), Postbus 201, 3730 AE De Bilt, The Netherlands There has been considerable recent interest in paleoclimate reconstructions of the temperature history of the last millennium. A wide variety of techniques have been used. The interrelation among the techniques is sometimes unclear, as different studies often use distinct data sources as well as distinct methodologies. Here recent work is reviewed and some new calculations performed with an aim to clarifying the consequences of the different approaches used. A range of proxy data collections introduced by different authors is used to estimate Northern Hemispheric annual mean temperatures with two reconstruction algorithms: (1) inverse regression and, (2) compositing followed by variance matching (CVM). It is found that inverse regression tends to give large weighting to a small number of proxies and that the second approach (CVM) is more robust to varying proxy input. The choice of proxy records is one reason why different reconstructions show different ranges. A reconstruction using 13 proxy records extending back to AD 1000 shows a maximum pre-industrial temperature of 0.25 K (relative to the 1866 to 1970 mean). The standard error on this estimate, based on the residual in the calibration period, is 0.14 K. Instrumental temperatures for two recent years (1998 and 2005) have exceeded the pre-industrial estimated maximum by more than 4 standard deviations of the calibration period residual. Adcock, R J.: A problem in least squares, The Analyst, 5, 53–54, 1878. Allen, M R. and Stott, P A.: Estimating signal amplitudes in optimal fingerprinting, Part I: Theory, Clim. Dynam., 21, 477–491, 2003. Arrhenius, S.: On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground, Philosophical Magazine, 41, 237–276, 1896. Bartholin, T. and Karlén, W.: Dendrokronologi i Lapland, Dendrokronologiska Sällskapets Medelanden, 4, 3–16, 1983. Bartlett, M., Chapman, D S., and Harris, R N.: Snow effect on North American ground temperatures 1950–2002, J. Geophys. Res., 110, F03 008, doi:10.1029/2005JF000293, 2005. Bauer, E., Claussen, M., Brovkin, V., and Huenerbein, A.: Assessing climate forcings of the Earth system for the past millennium, Geophys. Res. Lett, 30(6), 1276, doi:10.1029/2002GL016639, 2003. Bernabo, J C.: Quantitative estimates of temperature changes over the last 2700 years in Michigan based on pollen data, Quat. Res, 15, 143–159, 1981. Boninsegna, J A.: South American dendroclimatological records, Climate Since A.D. 1500, edited by: Bradley, R. S. and Jones, P. D., Routledge, 446–462, 1992. Bradley, R S., Hughes, M K., and Diaz, H F.: Climate in medieval time, Climate in medieval time, Science, 302, 404–405, 2003. Briffa, K R.: Annual climate variability in the Holocene: interpreting the message of ancient trees, Quart. Sci. Rev, 19, 87–105, 2000. Briffa, K R. and Osborn, T J.: Seeing the wood from the trees, Science, 284, 926–927, 1999. Briffa, K R., Jones, P D., Bartholin, T S., Eckstein, D., Schweingruber, F H., Karlén, W., Zetterberg, P., and Eronen, M.: Fennoscandian summers from A.D. 500: temperature changes on short and long time scales, Clim. Dynam., 7, 111–119, 1992. Briffa, K R., Jones, P D., Schweingruber, F H., Shiyatov, S G., and Cook, E R.: Unusual twentieth-century summer warmth in a 1,000-year temperature record from Siberia, Nature, 376, 156–159, 1995. Briffa, K R., Jones, P D., Schweingruber, F H., Karle´n, W., and Shiyatov, S G.: Tree-ring variables as proxy-climate indicators: Problems with low-frequency signals, NATO ASI Ser, Ser. I, vol. 41, edited by: Jones, P. D., Bradley, R. S., and Jouzel, J., pp. 9–41, Springer-Verlag, New York, 1996. Briffa, K R., Schweingruber, F H., Jones, P D., Osborn, T J., Shiyatov, S G., and Vaganov, E A.: Reduced sensitivity of recent tree-growth to temperature at high northern latitudes, Nature, 391, 678–682, 1998. Briffa, K R., Osborn, T J., Schweingruber, F H., Harris, I C., Jones, P D., Shiyatov, S G., and Vaganov, E A.: Low-frequency temperature variations from a northern tree ring density network, J. Geophys. Res., 106(D3), 2929–2941, doi:2000JD900617, 2001. Briffa, K R., Osborn, T J., Schweingruber, F H., Jones, P D., Shiyatov, S G., and Vaganov, E A.: Tree-ring width and density data around the Northern Hemisphere: Part 1, local and regional climate signals, The Holocene, 12, 737–757, 2002. Bürger, G. and Cubasch, U.: Are multiproxy climate reconstructions robust?, Geophys. Res. Lett., 32, L23 711, doi:10.1029/2005GL024155, 2005. Bürger, G., Fast, I., and Cubasch, U.: Climate reconstruction by regression - 32 variations on a theme, Tellus A, 58(2), 227–235, 2006. Chapman, D S., Bartlett, M G., and Harris, R N.: Comment on "Ground vs. surface air temperature trends: Implications for borehole surface temperature reconstructions", by Mann, M. and Schmidt, G., Geophys. Res. Lett., 31(7), L07205, doi:10.1029/2003GL019054, 2004. Chbouki, N.: Spatio-temporal characteristics of drought as inferred from tree-ring data in Morocco, Ph.D. thesis, University of Arizona, Tucson, Arizona, 1992. Clow, G.: Temporal resolution of surface-temperature histories inferred from borehole temperature measurements, Global Planet. Change, 98, 81–86, 1992. Cook, E. and Peters, K.: Calculating unbiased tree-ring indices for the study of climatic and environmental change, The Holocene, 7, 361–370, 1997. Cook, E R., Bird, T., Peterson, M., Barbetti, M., Buckley, B., D'Arrigo, R., Francey, R., and Tans, P.: Climatic change in Tasmania inferred from a 1089-year tree-ring chronology of subalpine huon pine, Science, 253, 1266–1268, 1991. Cook, E R., Briffa, K R., Meko, D M., Graybill, D S., and Funkhouser, G.: The 'segment length curse' in long tree-ring chronology development for paleoclimatic studies, The Holocene, 5(2), 229–237, 1995. Cook, E R., Esper, J., and D'Arrigo, R D.: Extra-tropical Northern Hemisphere land temperature variability over the past 1000 years, Quat. Sci. Rev., 23, 2063–2074, 2004. Cronin, T M., Dwyer, G S., Kamiya, T., Schwede, S., and Willard, D A.: Medieval Warm Period, Global Planet. Change, 36, 17–29, 2003. Crowley, T J.: Causes of climate change over the past 1000 years, Science, 289, 270–277, 2000. Crowley, T J. and Lowery, T.: How Warm Was the Medieval Warm Period? A comment on "Man-made versus natural climate change", Ambio, 29, 51–54, 2000. Dahl-Jensen, D., Mosegaard, K., Gundestrup, N., Clow, G D., Johnsen, S J., Hansen, A W., and Balling, N.: Past temperatures directly from the Greenland Ice Sheet, Science, 282, 268–271, 1998. D'Arrigo, R., Wilson, R., and Jacoby, G.: On the long-term context for late twentieth century warming, J. Geophys. Res., 111, D03103, doi:10.1029/2005JD006352, 2006. Davis, B., Brewer, S., Stevenson, A., and Guiot, J.: The temperature of Europe during the Holocene reconstructed from pollen data, Quat. Sci. Rev., 22, 1701–1716, 2003. Esper, J., Cook, E R., and Schweingruber, F H.: Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability, Science, 295, 2250–2253, 2002. Esper, J., Cook, E R., Krusic, P J., Peters, K., and Schweingruber, F H.: Tests of the RCS method for preserving low-frequency variability in long tree-ring chronologies, Tree-Ring Res., 59, 81–98, 2003. Esper, J., Frank, D C., and Wilson, R. J S.: Climate reconstructions – low frequency ambition and high frequency ratification, EOS, 85, 113, 120, 2004. Esper, J., Frank, D C., Wilson, R. J S., and Briffa, K R.: Effect of scaling and regression on reconstructed temperature amplitude for the past millennium, Geophys. Res. Lett., 32(7), L07711, doi:10.1029/2004GL021236, 2005. Ferguson, C W. and Graybill, D A.: Dendrochronology of bristlecone pine: a progress report, Radiocarbon, 25, 287–288, 1983. Fisher, D A., Koerner, R M., Kuivinen, K., Clausen, H B., Johnsen, S J., Steffensen, J P., Gundestrup, N., and Hammer, C U.: Inter-comparison of ice core and precipitation records from sites in Canada and Greenland over the last 3500 years and over the last few centuries in detail using EOF techniques, NATO ASI Ser, Ser. I, vol. 41, edited by: Jones, P. D., Bradley, R. S., and Jouzel, J., pp. 297–328, Springer-Verlag, New York, 1996. Folland, C., Karl, T., Christy, J., Clarke, R., Gruza, G., Jouzel, J., Mann, M., Oerlemans, J., Salinger, M., and Wang, S.-W.: Observed Climate Variability and Change, in: Climate Change 2001: The Sciencific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Houghton, J T., Ding, Y., Griggs, D., Noguer, M., van~der Linden, P J., and Xiaosu, D., chap 6, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2001. Foukal, P., North, G., and Wigley, T.: A stellar view on solar variations and climate, Science, 306, 68–69, 2004. Fritts, H.: Tree rings and climate, Academic Press, New York, 1976. Gajewski, K.: Late Holocene climate changes in eastern North America estimated from pollen data, Quat. Res., 29, 255–262, 1988. González-Rouco, F., von Storch, H., and Zorita, E.: Deep soil temperature as proxy for surface air-temperature in a coupled model simulation of the last thousand years, Geophys. Res. Lett., 30(21), 2116, doi:10.1029/2003GL018 264, 2003. Goosse, H., Renssen, H., Timmermann, A., and Bradley, R S.: Internal and forced climate variability during the last millennium: a model-data comparison using ensemble simulations, Quat. Sci. Rev., 24, 1345–1360, 2005. Graybill, D A. and Idso, S B.: Detecting the aerial fertilization effect of atmospheric CO2 enrichment in tree-ring chronologies, Global Biogeochem. Cycles, 7, 81–95, 1993. Grinstead, C. and Snell, J.: Introduction to Probability, American Mathematical Society, Providence, Rhode Island, second revised edn., 1997. Grudd, H., Briffa, K R., Karlén, W., Bartholin, T S., Jones, P D., and Kromer, B.: A 7400-year tree-ring chronology in northern Swedish Lapland: natural climatic variability expressed on annual to millennial timescales, The Holocene, 12, 657–666, 2002. Gupta, A K., Anderson, D M., and Overpeck, J T.: Abrupt changes in the Asian southwest monsoon during the Holocene and their links to the North Atlantic Ocean, Nature, 421, 354– 357, 2003. Hantemirov, R M. and Shiyatov, S. G A.: A continuous multimillennial ring-width chronology in Yamal, northwestern Russia, The Holocene, 12, 717–726, 2002. Hegerl, G., Crowley, T., Hyde, W., and Frame, D.: Climate sensitivity constrained by temperature reconstructions over the past seven centuries, Nature, 440, 1029–1032, 2006. Hegerl, G., Crowley, T., Allen, M., Hyde, W., Pollack, H., Smerdon, J., and Zorita, E.: Detection of human influence on a new, validated, 1500 year temperature reconstruction, J. Climate, 20, 650–666, 2007a. Hegerl, G., Zwiers, F W., Braconnot, P., Gillett, N., Luo, Y., Orsini, J M., Nicholls, N., Penner, J., and Stott, P.: Understanding and Attributing Climate Change, in: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K., Tignor, M., and Miller, H., chap 10, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2007b. Hosking, J. R M.: Modeling persistence in hydrological time series using fractional differencing, Water Resour. Res., 20(12), 1898–1908, 1984. Huang, S.: Merging information from different resources for new insight into climate change in the past and future, Geophys. Res. Lett., 31, L13205, doi:10.1029/2004GL019781, 2004. Huang, S., Pollack, H N., and Shen, P Y.: Temperature trends over the past five centuries reconstructed from borehole temperatures, Nature, 403, 756–758, 2000. Hughes, M K. and Diaz, H F.: Was there a `Medieval Warm Period' and if so, where and when?, Clim. Change, 26, 109–142, 1994. Hughes, M K. and Funkhouser, G.: Frequency-dependent climate signal in upper and lower forest border trees in the mountains of the Great Basin, Clim. Change, 59, 233–244, 2003. Huybers, P.: comment on "Hockey sticks, principal components, and spurious significance" by McIntyre and McKitrick [2005], Geophys. Res. Lett., 32, L20 705, doi:10.1029/2005GL023395, 2005. Jansen, E., Overpeck, J., Briffa, K., Duplessy, J.-C., Joos, F., Masson-Delmotte, V., Olago, D., Otto-Bliesner, B., Peltier, W., Rahmstorf, S., Ramesh, R., Raynaud, D., Rind, D., Solomina, O., Villalba, R., and Zhang, D.: Palaeoclimate, in: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K., Tignor, M., and Miller, H., chap 6, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2007. Jones, P D. and Mann, M E.: Climate over past millennia, Rev. Geophys., 42, RG2002, doi:10.1029/2003RG000143, 2004. Jones, P D. and Moberg, A.: Hemispheric and large-scale surface air temperature variations: An extensive revision and an update to 2001, J. Climate, 16, 206–223, 2003. Jones, P D., Wigley, T. M L., and Wright, P B.: Global temperature variations between 1861 and 1984, Nature, 332, 430–434, 1986. Jones, P D., Briffa, K R., Barnett, T P., and Tett, S. F B.: High-Resolution Paleoclimatic Records for the Last Millennium: Interpretation, Integration and Comparison with Circulation Model Control-Run Temperatures, Holocene, 8, 455–471, 1998. Körner, C., Asshoff, R., Bignucolo, O., Hättenschwiler, S., Keel, S G., Peláez-Riedl, S., Pepin, S., Siegwolf, R. T W., and Zotz, G.: Carbon Flux and Growth in Mature Deciduous Forest Trees Exposed to Elevated CO2, Science, 309, 1360–1362, 2005. LaMarche, V C.: Frequency-dependent relationships between tree-ring series along an ecological gradient and some dendroclimatic implications, Tree-Ring Bull., 34, 1–20, 1974. Lara, A. and Villalba, R.: A 3620-year temperature record from Fitzroya cupressoides tree rings in southern South America, Science, 260, 1104–1106, 1993. Lean, J L., Wang, Y M., and Sheeley Jr., N R.: The effect of increasing solar activity on the Sun's total and open magnetic flux during multiple cycles: Implications for solar forcing of climate, Geophys. Res. Lett., 29(24), 2224, doi:10.1029/2002GL015880, 2002. Little, R. J A. and Rubin, D B.: Statistical analysis with missing data, John Wiley and Sons, New York, pp. 278, 1987. Lloyd, A H. and Graumlich, L J.: Holocene dynamics of treeline forests in the Sierra Nevada, Ecology, 78, 1199–1210, 1997. Mann, M E. and Jones, P D.: Global surface temperatures over the past two millennia, Geophys. Res. Lett., 30(15), 1820, doi:10.1029/2003GL017814, 2003. Mann, M E., Bradley, R S., and Hughes, M K.: Global-scale temperature patterns and climate forcing over the past six centuries, Nature, 392, 779–787, 1998. Mann, M E., Bradley, R S., and Hughes, M K.: Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations, Geophys. Res. Lett., 26(6), 759–762, 1999. Mann, M E., Ammann, C., Bradley, R., Briffa, K., Jones, P., Osborn, T., Crowley, T., Hughes, M., Oppenheimer, M., Overpeck, J., Rutherford, S., Trenberth, K., and Wigley, T.: On past temperatures and anomalous late-20th century warmth, Eos Trans. AGU, 84(27), 256–258, 2003a. Mann, M E., Ammann, C., Bradley, R., Briffa, K., Jones, P., Osborn, T., Crowley, T., Hughes, M., Oppenheimer, M., Overpeck, J., Rutherford, S., Trenberth, K., and Wigley, T.: Response [to comments on "On past temperatures and anomalous late-20th century warmth"], Eos Trans. AGU, 84(44), 473–474, 2003b. Mann, M E., Rutherford, S., Bradley, R S., Hughes, M K., and Keimig, F T.: Optimal surface temperature reconstructions using terrestrial borehole data, J. Geophys. Res., 108(D7), 4203, doi:10.1029/2002JD002532, 2003c. Mann, M E., Bradley, R S., and Hughes, M K.: Corrigendum: Global-scale temperature patterns and climate forcing over the past six centuries, Nature, 430, 105, doi:10.1038/nature02478, 2004. Mann, M E., Rutherford, S., Wahl, E., and Ammann, C.: Testing the fidelity of methods used in proxy-based reconstructions of past climate, J. Climate, 18, 4097–4107, 2005. Mann, M E., Rutherford, S., Wahl, E., and Ammann, C.: Robustness of proxy-based climate field reconstruction methods, J. Geophys. Res., 112, D12 109, doi:10.1029/2006JD008272, 2007. Manning, M M., Petit, M., Easterling, D., Murphy, J., Patwardhan, A., Rogner, H.-H., Swart, R., and Yohe, G.: IPCC Workshop on Describing Scientific Uncertainties in Climate Change to Support Analysis of Risk and of Options: Workshop report, Intergovernmental Panel on Climate Change (IPCC), Geneva, 2004. McIntyre, S. and McKitrick, R.: Corrections to the Mann et al (1998) Proxy Data Based and Northern Hemispheric Average Temperature Series, Energy and Environment, 14, 751–771, 2003. McIntyre, S. and McKitrick, R.: Hockey sticks, principal components, and spurious significance, Geophys. Res. Lett., 32, L03 710, doi:10.1029/2004GL02, 2005a. McIntyre, S. and McKitrick, R.: The M&M critique of the MBH1998 northern hemisphere climate index: update and implications, Energy and Environment, 16, 69–100, 2005b. McIntyre, S. and McKitrick, R.: Reply to comment by Huybers on "Hockey sticks, principal components, and spurious significance", Geophys. Res. Lett., 32, L20 713, doi:10.1029/2005GL023586, 2005c. McIntyre, S. and McKitrick, R.: Reply to comment by von Storch and Zorita on `Hockey sticks, principal components, and spurious significance', Geophys. Res. Lett., 32, L20 714, doi:10.1029/2005GL023089, 2005d. Mitchell, J. F B., Karoly, D J., Hegerl, G C., Zwiers, F W., Allen, M R., and Marengo, J.: Detection of climate change and attribution of causes, in: Climate Change 2001: The Sciencific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Houghton, J T., Ding, Y., Griggs, D., Noguer, M., van~der Linden, P J., and Xiaosu, D., chap 6, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2001. Moberg, A., Sonechkin, D M., Holmgren, K., Datsenko, N M., and Karlén, W.: Highly variable Northern Hemisphere temperatures reconstructed from low- and high-reslution proxy data, Nature, 433, 613–617, 2005. Naurzbaev, M M. and Vaganov, E A.: 1957-year tree-ring chronology of eastern part of Taymir, Siberian Journal of Ecology, 6, 159–168, 1999. Oerlemans, J H.: Extracting a Climate Signal from 169 Glacier Records, Science, 308, 675–677, 2005. Osborn, T J. and Briffa, K R.: The spatial extent of 20th-Century warmth in the context of the past 1200 years, Science, 313, 841–844, 2006. Osborn, T J., Briffa, K R., and Jones, P D.: Adjusting variance for sample-size in tree-ring chronologies and other regional mean timeseries, Dendrochronologia, 15, 89–99, 1997. Pearson, K.: Mathematical Contributions to the Theory of Evolution. III. Regression, Heredity and Panmixia, Philosophical Transactions of the Royal Society A, 187, 253–318, 1896. Pollack, H N. and Smerdon, J E.: Borehole climate reconstructions: Spatial structure and hemispheric averages, J. Geophys. Res, 109(D), 11 106, doi:10.1029/2003JD004163, 2004. Pollack, H N., Huang, S., and Shen, P Y.: Climate change record in subsurface temperatures: A global perspective, Science, 282, 279–281, 1998. Rutherford, S. and Mann, M E.: Correction to "Optimal surface temperature reconstructions using terrestrial borehole data" by Mann et al., J. Geophys. Res., 109, D11107, doi:10.1029/2003JD004290, 2004. Rutherford, S., Mann, M E., Osborn, T J., Bradley, R S., Briffa, K R., Hughes, M K., and Jones, P D.: Proxy-based Northern Hemisphere surface temperature reconstructions: Sensitivity to method, predictor network, target season, J. Climate, 18, 2308–2329, 2005. Schneider, T.: Analysis of Incomplete Climate Data: Estimation of Mean Values and Covariance Matrices and Imputation of Missing Values, J. Climate, 14, 853–871, 2001. Serre-Bachet, F., Martinelli, N., Pignatelli, O., Guiot, J., and Tessier, L.: Evolution des températures du Nord-Est de L'Italie depuis 1500 AD. Reconstruction d'après les cernes des arbres, Dendrochronologia, 9, 213–219, 1991. Shiyatov, S G.: The upper timberline dynamics during the last 1100 years in the Polar Ural mountains, in: Oscillations of the Alpine and Polar K Tree Limits in the Holocene, edited by: Frenzel, B., Eronen, M., Vorren, K., and Glaser, B., pp. 195–203, Fischer, Stuttgart, Germany, 1993. Solomon, S., Qin, D., Manning, M., Alley, R., Berntsen, T., Bindoff, N., Chen, Z., Chidthaisong, A., Gregory, J., Hegerl, G., Heimann, M., Hewitson, B., Hoskins, B., Joos, F., Jouzel, J., Kattsov, V., Lohmann, U., Matsuno, T., Molina, M., Nicholls, N., Overpeck, J., Raga, G., Ramaswamy, V., Ren, J., Rusticucci, M., Somerville, R., Stocker, T., Whetton, P., Wood, R., and Wratt, D.: Technical Summary, in: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K., Tignor, M., and Miller, H., Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2007. Soon, W. and Baliunas, S.: Proxy climatic and environmental changes over the past 1000 years, Clim. Res., 23, 89–110, 2003. Soon, W., Baliunas, S., and Legates, D R.: Comments on "On past temperatures and anomalous late-20th century warmth", Eos Trans. AGU, 84(44), 473–476, 2003. Tan, M., Liu, T., Hou, J., Qin, X., Zhang, H., and Tieying, L.: Cyclic rapid warming on centennial-scale revealed by a 2650-year stalagmite record of warm season temperature, Geophys. Res. Lett., 30, 1617, doi:10.1029/2003GL017352, 2003. Thompson, L G.: Ice core evidence from Peru and China, in Climate Since A.D. 1500, edited by: R. S. Bradley and P. D. Jones, pp. 517–548, New York, 1992. von Storch, H. and Zorita, E.: Comment on `Hockey sticks, principal components, and spurious significance' by S. McIntyre and R. McKitrick, Geophys. Res. Lett., 32, L20 701, doi:10.1029/2005GL022753, 2005. von Storch, H., Zorita, E., Jones, J M., Dimitriev, Y., and Tett, S. F B.: Reconstructing Past Climate from Noisy Data, Science, 2004. von Storch, H., Zorita, E., Jones, J M., González-Rouco, J F., and Tett, S. F B.: Response to comment on "Reconstructing past climate from noisy data", Science, 312, 5782, \doi10.1126/science.1121571, 2006. Wahl, E R. and Ammann, C M.: Robustness of the Mann, Bradley, Hughes Reconstruction of Surface Temperatures: Examination of Criticisms Based on the Nature and Processing of Proxy Climate Evidence, Climatic Change, in press, 2007. Weber, S L.: A timescale analysis of the NH temperature response to volcanic and solar forcing in the past millenium, Clim. Past, 1, 9–17, 2005. Weber, S L., Crowley, T J., and der Schrier, G V.: Solar irradiance forcing of centennial climate variability during the Holocene, Clim. Dynam., 22, 539–553, 2004. Wilmking, M., D'Arrigo, R., Jacoby, G C., and Juday, G P.: Increased temperature sensitivity and divergent growth trends in circumpolar boreal forests, Geophys. Res. Lett., 32, L15 715, doi:10.1029/2005GL023331, 2005. Yang, B., Bräuning, A., Johnson, K R., and Yafeng, S.: General characteristics of temperature variation in China during the last two millennia, Geophys. Res. Lett., 29(9), 1324, doi:10.1029/2001GL014485, 2002.