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Six Thousand Years of Chinese Climate
Hong, Y.T., Jiang, H.B., Liu, T.S., Zhou, L.P., Beer, J., Li, H.D., Leng, X.T., Hong, B. and Qin, X.G. 2000. Response of climate to solar forcing recorded in a 6000-year delta18O time-series of Chinese peat cellulose. The Holocene 10: 1-7.

What was done
The authors developed a 6000-year high-resolution delta18O record from plant cellulose deposited in a peat bog in the Jilin Province of China (42 20' N, 126 22' E) from which they inferred the temperature history of that location over the past six millennia. They then compared this record with a previously-derived Delta14C tree-ring record that is representative of the intensity of solar activity over this period.

What was learned
The study area was relatively cold between 4000 and 2600 BC. Then it warmed fairly continuously until it reached the maximum warmth of the record about 1600 BC, after which it fluctuated about this warm mean for approximately 2000 years. Starting about AD 350, however, the climate began to cool, with the most dramatic cold associated with three temperature minima centered at about AD 1550, 1650 and 1750, corresponding to the most severe cold of the Little Ice Age.

Of particular note is the authors' finding of "an obvious warm period represented by the high delta18O from around AD 1100 to 1200 which may correspond to the Medieval Warm Epoch of Europe." They also report that "at that time, the northern boundary of the cultivation of citrus tree (Citrus reticulata Blanco) and Boehmeria nivea (a perennial herb), both subtropical and thermophilous plants, moved gradually into the northern part of China, and it has been estimated that the annual mean temperature was 0.9-1.0C higher than at present."

Last of all, the authors note "there is a remarkable, nearly one to one, correspondence between the changes of atmospheric Delta14C and the variation in delta18O of the peat cellulose."

What it means
The authors conclude that the temperature history of the past 6000 years at the site of their study has been "forced mainly by solar variability." Their findings also demonstrate that for this part of China there was indeed a Medieval Warm Period that corresponded to that of Europe, and that it was indeed warmer at that point in time and space than it is presently, which clearly contradicts the claims of those who are trying to convince the world that we are currently living in the warmest period of the past millennium and that the Medieval Warm period was neither really warm nor global.

Reviewed 1 July 2000