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The Medieval Warm Period at Lake Joux, Swiss Jura Mountains
Magny, M., Peyron, O., Gauthier, E., Vanniere, B., Millet, L. and Vermot-Desroches, B. 2011. Quantitative estimates of temperature and precipitation changes over the last millennium from pollen and lake-level data at Lake Joux, Swiss Jura Mountains. Quaternary Research 75: 45-54.

The authors write that "present-day global warming has provoked an increasing interest in the reconstruction of climate changes over the last millennium (Guiot et al., 2005; Jones et al., 2009)," which time interval, as they describe it, is "characterized by a succession of distinct climatic phases, i.e. a Medieval Warm Period (MWP) followed by a long cooler Little Ice Age (LIA) and finally by a post-industrial rapid increase in temperature," which we at CO2Science refer to as the initial phase of the Current Warm Period (CWP).

What was done
Working at Lake Joux (46°36'N, 6°15'E) at an altitude of 1006 meters above sea level (a.s.l.) in the Swiss Jura Mountains, Magny et al. employed a multi-proxy approach with pollen and lake-level data to develop a 1000-year history of the mean temperature of the warmest month of the year (MTWA, which was July at Lake Joux), based on the Modern Analogue Technique, which procedure is described by them as "a commonly used and accepted method for the reconstruction of Lateglacial and Holocene climate oscillations from continental and marine sequences," citing the confirming works of Guiot et al. (1993), Cheddadi et al., (1997), Davis et al. (2003), Peyron et al. (2005), Kotthoff et al. (2008) and Pross et al. (2009).

What was learned
The six scientists say their data "give evidence of the successive climate periods generally recognized within the last 1000 years," which they describe as "a MWP between ca. AD 1100 and 1320, (2) a LIA which, in the Joux Valley, initiated as early as ca. AD 1350 and ended at ca. AD 1870, and (3) a last warmer and drier period," which we at CO2 Science generally refer to as the beginning of the Current Warm Period (CWP).

What it means
"Considering the question of present-day global warming on a regional scale," in the words of Magny et al., "the increase in MTWA by ca. 1.6°C observed at Laoura (1100 m a.s.l., near the Joux basin) for the period 1991-2008, when compared to the reference period 1961-1990, still appears to be in the range of the positive temperature anomaly reconstructed at Lake Joux ca. AD 1300 during the late MWP," and they note that "meteorological data observed at La Brevine (1043 m a.s.l., also near the Joux basin) suggest a similar pattern with an increase in MTWA by 1°C over the period 1991-2008" relative to 1961-1990. Yet both of these late-20th/early-21st century temperature increases fall significantly short of that reached during the MWP, when the temperature at Joux Lake exceeded that of the 1961-1990 reference period by fully 2.0°C.

In light of these findings, it would appear that the peak warmth of the MWP at Lake Joux exceeded that of the CWP at that location by something on the order of 0.4-1.0°C, in harmony with similar findings obtained at numerous other locations around the world that we have documented in our Medieval Warm Period Project. And these observations clearly indicate that temperatures even warmer than those of the present can occur with much less CO2 in the air than there is today, suggesting that there is no compelling reason to attribute earth's current level of warmth to the atmosphere's current high CO2 concentration.

Cheddadi, R., Yu, G., Guiot, J., Harrison, S.P. and Prentice, I.C. 1997. The climate of Europe 6000 years ago. Climate Dynamics 13: 1-9.

Davis, B.A.S., Brewer, S., Stevenson, A.C. and Guiot,J. 2003. The temperature of Europe during the Holocene reconstructed from pollen data. Quaternary Science Reviews 22: 1701-1716.

Guiot, J., Harrison, S.P. and Prentice, I.C. 1993. Reconstruction of Holocene pattern of moisture in Europe using pollen and lake-level data. Quaternary Research 40: 139-149.

Guiot, J., Nicault, A., Rathgeber, C., Edouard, J.L., Guibal, F., Pichard, G. and Till, G. 2005. Last-millennium summer-temperature variations in western Europe based on proxy data. The Holocene 15: 489-500.

Jones, P.D., Briffa, K.R., Osborn, T.J., Lough, J.M., van Ommen, T.D., Vinther, B.M., Luterbacher,J., Wahl, E.R., Zwiers, F.W., Mann, M.E., Schmidt, G.A., Ammann, C.M., Buckley, B.M., Cobb, K.M., Esper, J., Goosse, H., Graham, N., Jansen, E., Kiefer, T., Kull, C., Kuttel, M., Mosley-Thompson, E., Overpeck, J.T., Riedwyl, N., Schulz, M., Tudhope, A.W., Villalba, R., Wanner, H., Wolff, E. and Xoplaki, E. 2009. High-resolution palaeoclimatology of the last millennium: a review of current status and future prospects. The Holocene 19: 3-49.

Kotthoff, U., Pross, J., Muller, U.C., Peyron, O., Schmiedle, G., Schulz, H. and Bordon, A. 2008. Climate dynamics in the borderlands of the Aegean Sea during formation of sapropel 1 deduced from a marine pollen record. Quaternary Science Reviews 27: 832-845.

Peyron, O., Begeot, C., Brewer, S., Heiri, O., Millet, L., Ruffaldi, P., Van Campo, E. and Yu, G. 2005. Late-Glacial climatic changes in Eastern France (Lake Lautrey) from pollen, lake-levels, and chironomids. Quaternary Research 64: 197-211.

Pross, J., Kotthoff, U., Muler, U.C., Peyron, O., Dormoy, I., Schmiedle, G., Kalaitzidis, S. and Smith, A.M. 2009. Massive perturbation in terrestrial ecosystems of the Eastern Mediterranean region associated with the 8.2 kyr climatic event. Geology 37: 887-890.

Reviewed 15 June 2011