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The Medieval Warm Period in the Central Alps of Austria
Volume 8, Number 30: 27 July 2005

In an important new study of a precisely dated δ18O record with better than decadal resolution that they derived from a stalagmite recovered from Spannagel Cave in the Central Alps of Austria, Mangini et al. (2005) develop a highly-resolved record of temperature at high elevation (approximately 2500 meters above sea level) during the past 2000 years, based on a transfer function they derived from a comparison of their δ18O data with the reconstructed temperature history of post-1500 Europe that was developed by Luterbacher et al. (2004).

The lowest temperatures of the past two millennia, according to the new record, occurred during the Little Ice Age (AD 1400-1850), while the highest temperatures were found in the Medieval Warm Period (MWP: AD 800-1300). Furthermore, Mangini et al. say that the highest temperatures of the MWP were "slightly higher than those of the top section of the stalagmite (1950 AD) and higher than the present-day temperature." In fact, at three different points during the MWP, their data indicate temperature spikes in excess of 1C above present (1995-1998) temperatures.

Mangini et al. additionally report that their temperature reconstruction compares well with reconstructions developed from Greenland ice cores (Muller and Gordon, 2000), Bermuda Rise ocean-bottom sediments (Keigwin, 1996), and glacier tongue advances and retreats in the Alps (Holzhauser, 1997; Wanner et al., 2000), as well as with the Northern Hemispheric temperature reconstruction of Moberg et al. (2005). Considered together, they say these several data sets "indicate that the MWP was a climatically distinct period in the Northern Hemisphere," emphasizing that "this conclusion is in strong contradiction to the temperature reconstruction by the IPCC, which only sees the last 100 years as a period of increased temperature during the last 2000 years."

In a second severe blow to IPCC dogma, Mangini et al. found "a high correlation between δ18O and δ14C, that reflects the amount of radiocarbon in the upper atmosphere," and they note that this correlation "suggests that solar variability was a major driver of climate in Central Europe during the past 2 millennia." In this regard, they report that "the maxima of δ18O coincide with solar minima (Dalton, Maunder, Sporer, Wolf, as well as with minima at around AD 700, 500 and 300)," and that "the coldest period between 1688 and 1698 coincided with the Maunder Minimum." Also, in a linear-model analysis of the percent of variance of their full temperature reconstruction that is individually explained by solar and CO2 forcing, they found that the impact of the sun was fully 279 times greater than that of the air's CO2 concentration, noting that "the flat evolution of CO2 during the first 19 centuries yields almost vanishing correlation coefficients with the temperature reconstructions."

Clearly, the IPCC-endorsed hockeystick temperature history of Mann et al. (1998, 1999) does not appear to reflect the true thermal history of the Northern Hemisphere over the past thousand years, nor, by inference, does the hockeystick temperature history of Mann and Jones (2003) appear to reflect the true thermal history of the world as a whole over the past two millennia. In addition, both sets of studies, as well as the IPCC itself, appear to be focusing on the wrong instigator of climate change over these periods, i.e., CO2 in lieu of solar activity. Hence, we agree with the UK's House of Lords Select Committee on Economic Affairs (2005) that "if there are historical periods of marked temperature increase, it seems to us it is important to know why these occurred," and that the issue should be pursued in depth in the next IPCC Assessment. We additionally urge that the study of Mangini et al. figure prominently in that evaluation, and that there be no steps taken to curtail anthropogenic CO2 emissions until that evaluation is complete.

Sherwood, Keith and Craig Idso

References
Holzhauser, H. 1997. Fluctuations of the Grosser Aletsch Glacier and the Gorner Glacier during the last 3200 years: new results. In: Frenzel, B. (Ed.) Glacier Fluctuations During the Holocene. Fischer, Stuttgart, Germany, pp. 35-58.

House of Lords Select Committee on Economic Affairs. 2005. Second Report of Session 2005-06: The Economic of Climate Change.

Keigwin, L.D. 1996. The Little Ice Age and Medieval Warm Period in the Sargasso Sea. Science 274: 1503-1508.

Luterbacher, J., Dietrich, D., Xoplaki, E., Grosjean, M. and Wanner, H. 2004. European seasonal and annual temperature variability trends, and extremes since 1500. Science 303: 1499-1503.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1998. Global-scale temperature patterns and climate forcing over the past six centuries. Nature 392: 779-787.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1999. Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters 26: 759-762.

Mann, M.E. and Jones, P.D. 2003. Global surface temperatures over the past two millennia. Geophysical Research Letters 30: 10.1029/2003GL017814.

Mangini, A., Spotl, C. and Verdes, P. 2005. Reconstruction of temperature in the Central Alps during the past 2000 yr from a δ18O stalagmite record. Earth and Planetary Science Letters 235: 741-751.

Moberg, A., Sonechkin, D.M., Holmgren, K., Datsenko, N.M. and Karlen, W. 2005. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature 433: 613-617.

Muller, R.A. and Gordon, J.M. 2000. Ice Ages and Astronomical Causes. Springer-Verlag, Berlin, Germany.

Wanner, H., Dimitrios, G., Luterbacher, J., Rickli, R., Salvisberg, E. and Schmutz, C. 2000. Klimawandel im Schweizer Alpenraum. VDF Hochschulverlag, Zurich, Switzerland.