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Chipping Away at the Hockeystick
Larocque-Tobler, I., Stewart, M.M., Quinlan, R., Traschel, M., Kamenik, C. and Grosjean, M. 2012. A last millennium temperature reconstruction using chironomids preserved in sediments of anoxic Seebergsee (Switzerland): consensus at local, regional and Central European scales. Quaternary Science Reviews 41: 49-56.

The authors write that "the climate of the last millennium is still controversial because too few high-resolution paleo-climate reconstructions exist to answer two key research questions," namely, (1) "Were the 'Medieval Climate Anomaly' (MCA) and the 'Little Ice Age' (LIA) of similar spatial extent and timing in Europe and in the Northern Hemisphere?" and (2) "Does the amplitude of climate change of the last century exceed the natural variability?"

What was done
Working with a lake sediment core extracted from the deepest point of Seebergsee (46°37'N, 7°28'E) in the northern Swiss Alps in AD 2005, Larocque-Tobler et al. employed chironomid head capsules preserved in the sediments to reconstruct mean July air temperatures for the past 1000 years, after which they compared their results to those of Larocque-Tobler et al. (2010) for another Swiss lake (Silvaplana in the eastern Alps), then to regional and European records of early instrumental data (Luterbacher et al., 2004; Auer et al., 2007; Bohm et al., 2010), as well as a composite of paleoclimate reconstructions from the Greater Alpine Region and to millennial scale climate reconstructions of the entire Northern Hemisphere (Mangini et al., 2005; Moberg et al., 2005; Osborn and Briffa, 2006), in order to address the two research questions that inspired their study and "to improve understanding of the climatic variability of the last millennium."

What was learned
The six scientists' work revealed that the peak warmth of the MCA just prior to AD 1200 was approximately 0.9°C greater than the peak warmth near the end of their record, as best we can determine from the graph of their data.

What it means
As more and more palaeo-temperature data are acquired, the IPCC-endorsed "hockeystick" temperature record of Mann et al. (1999) - which gives little indication of the existence of the MCA and shows recent temperatures towering over those of that earlier time period - is fading slowly into the night, as it is repudiated by ever more real-world data. And it's not just the most recent data of Larocque-Tobler et al. that refute the IPCC's view of this matter; for the group of six says that their newest temperature history is "mirrored by the chironomid reconstruction from Silvaplana and the Greater Alpine Region composite of reconstructions." And they add that "several other reconstructions from the Northern Hemisphere also show [recent] warm inferred temperatures that were not as warm as the MCA." In addition, and it's a big addition, we note that many more palaeoclimatic studies from all around the world - which are described and have their results tabulated in our Medieval Warm Period Project - likewise testify to the greater-than-current peak-warmth of the MCA.

Auer, I., Bohm, R., Jurkovic, A., Lipa, W., Orlik, A., Potzmann, R., Schoner, W., Ungersbok, M., Matulla, C., Briffa, K., Jones, P., Efthymiadis, D., Brunetti, M., Nanni, T., Maugeri, M., Mercalli, L., Mestre, O., Moisselin, J.-M., Begert, M., Muller-Westermeier, G., Kveton, V., Bochnicek, O., Stastny, P., Lapin, M., Szalai, S., Szentimrey, T., Cegnar, T., Dolinar, M., Gajic-Capka, M., Zaninovic, K., Majstorovic, M. and Nieplova, M. 2007. HISTALP: historical instrumental climatological surface time series of the Greater Alpine Region. International Journal of Climatology 27: 17-46.

Bohm, R., Jones, P.D., Hiebl, J., Brunetti, M., Frank, D. and Maugeri, M. 2010. The early instrumental warm bias: a solution for long central European temperatures series 1760-2007. Climatic Change 101: 41-67.

Larocque-Tobler, I., Grosjean, M., Heiri, O., Trachsel, M. and Kamenik, C. 2010. Thousand years of climate change reconstructed from chironomid subfossils preserved in varved lake Silvaplana, Engadine, Switzerland. Quaternary Science Reviews 29: 1940-1949.

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.

Mangini, A., Spotl, C. and Verdes, P. 2005. Reconstruction of temperature in the Central Alps during the past 2000 yr from a 18O stalagmite record. Earth and Planetary Science Letters 235: 741-751.

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.

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.

Osborn, T.J. and Briffa, K.R. 2006. The spatial extent of 20th-century warmth in the context of the past 1200 years. Science 311: 831-834.

Reviewed 19 September 2012