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The Medieval Warm Period and Little Ice Age in Switzerland
Filippi, M.L., Lambert, P., Hunziker, J., Kubler, B. and Bernasconi, S. 1999. Climatic and anthropogenic influence on the stable isotope record from bulk carbonates and ostracodes in Lake Neuchatel, Switzerland, during the last two millennia. Journal of Paleolimnology 21: 19-34.

What was done
The authors obtained stable isotope data (delta 18O and delta 13C) from bulk carbonate and ostracode calcite in a radiocarbon-dated sediment core removed from Lake Neuchatel in the western Swiss Lowlands at the foot of the Jura Mountains, which they used to reconstruct the climatic history of the region over the past 1500 years.

What was learned
According to the authors, the data suggest that mean annual air temperature dropped by about 1.5C during the transition from the Medieval Warm Period (MWP) to the Little Ice Age (LIA). They further state that "the warming during the 20th century does not seem to have fully compensated the cooling at the MWP-LIA transition" and that during the Medieval Warm Period, mean annual air temperatures were "on average higher than at present."

What it means
For some time now the climate alarmists have been claiming that temperatures during the latter part of the 20th century were the warmest of the past thousand years. According to the authors of this paper, however, that claim is false. Not only do their data indicate that this is so, but those of others do as well. Citing Keigwin (1996), for example, they note that "sea surface temperature (SST) reconstructions show that SST was ca. 1C cooler than today about 400 years ago and ca. 1C warmer than today during the MWP." And citing Bond et al. (1997), they note that the MWP and LIA are just the most recent manifestations of "a pervasive millennial-scale coupled atmosphere-ocean climate oscillation" that has absolutely nothing to do with variations in the air's CO2 content.

Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P. deMenocal, P., Priori, P., Cullen, H., Hajdes, I. and Bonani, G. 1997. A pervasive millennial-scale climate cycle in the North Atlantic: The Holocene and late glacial record. Science 278: 1257-1266.

Keigwin, L.D. 1996. The Little Ice Age and Medieval Warm Period in the Sargasso Sea. Science 174: 1504-1508.

Reviewed 15 November 2000