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Millennial-Scale Oscillation of Climate Recorded at Beijing
Ma, Z., Li, H., Xia, M., Ku, T., Peng, Z., Chen, Y. and Zhang, Z. 2003. Paleotemperature changes over the past 3000 years in eastern Beijing, China: A reconstruction based on Mg/Sr records in a stalagmite. Chinese Science Bulletin 48: 395-400.

What was done
Working with a stalagmite from Jingdong Cave about 90 km northeast of Beijing, the authors assessed the climatic history of the past 3000 years at 100-year intervals on the basis of 18O data, the Mg/Sr ratio, and the solid-liquid distribution coefficient of Mg.

What was learned
Between 200 and 500 years ago (aBP), the authors report "air temperature was about 1.2C lower than that of the present, corresponding to the Little Ice Age in Europe." Earlier, between 1000 and 1300 aBP, there was an equally aberrant but warm period that peaked at about 1100 aBP, which they say "corresponded to the Medieval Warm Period ( AD900-1300) in Europe." This period of peak warmth in the Chinese record had been preceded by what has come to be called the Dark Ages Cold period that in turn had been preceded by the Roman Warm Period, which in the stalagmite record is best defined by the much colder period that had preceded it.

What it means
The climate record derived from China's Jingdong Cave is just another example of what is being found in paleoclimate studies all around the world. There is an externally-forced millennial-scale climatic oscillation of probable solar origin that periodically brings the world relatively warmer and colder conditions, irrespective of whatever may or may not be happening to the air's CO2 content. The Modern Warm Period would thus appear to be nothing more than the most recent expression of this phenomenon.

Reviewed 20 August 2003