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The Temperature History of Eastern China Over the Past Two Millennia
Volume 8, Number 12: 23 March 2005

Ge et al. (2004) introduce their important study of two thousand years of reconstructed winter half-year temperatures of eastern China by stating that "it is important to study the temperature change during the past 2000 years for understanding the issues such as the greenhouse effect and global warming induced by human activities," stating additionally that "China has advantages in reconstructing historical climate change for its abundant documented historical records and other natural evidence obtained from tree rings, lake sediments, ice cores, and stalagmites."  That said, what did they find?

Perhaps the five climate scientists' most fundamental finding was the existence of "an about 1350-year periodicity in the historical temperature change," which revealed a number of multi-century warm and cold periods.  Preceding the Modern Warm Period, for example, was the Little Ice Age (LIA), which "in China," in their words, "began in the early 14th century (the 1320s) and ended in the beginning of the 20th century (the 1910s)."  It included four cold stages and three short warming phases.  The LIA, in turn, was preceded by the Medieval Warm Period, which Ge et al. say "began in the 930s and ended in the 1310s."  It was composed of two warm stages, each of over 100 years duration, and a shorter intervening cold stage.

Continuing further back in time, the Chinese scientists found a cold period from the 780s to the 920s and a warm period from the 570s to the 770s, which was in turn preceded by a cold period from the 210s to the 560s, which they say "was the only one comparable with [the] LIA for the past 2000 years."  This ultra-cold spell, of course, was the Dark Ages Cold Period that followed on the heels of the Roman Warm Period.

Since one of the purposes of their study was "to test whether the warming in the 20th century has exceeded the maximum magnitude in the past 2000 years," Ge et al. considered this question in some detail.  At the centennial scale, they report that "the temperature anomaly of the 20th century is not only lower than that of the later warm stage of the Medieval Warm Period (the 1200s~1310s), but also slightly lower than that of the warm period in the Sui and Tang dynasties (the 570s~770s) and the early warm stage of the Medieval Warm Period (the 930s~1100s)."

On a 30-year scale, they likewise report that "the warmest 30-year temperature anomaly in the 20th century is roughly equal to the warmest 30-year one in the Sui and Tang dynasties warm period, but a little lower than that of the Medieval Warm Period."  And on the decadal scale, they say that "the warmest decadal temperature anomaly in the 20th century is approximately at the same level of the warmest decade of the early stage of the Medieval Warm Period."

Last of all, Ge et al. additionally note that "although the warming rate in the early [our italics] 20th century has reached 1.1C per century, such a rapid change is not unique during the alternation from the cold period[s] to the warm period[s]" of the prior 2000 years.  For example, they report that the per-century warming rate from the 480s~500s to the 570s~590s was 1.3C, from the 1140s~1160s to the 1230s~1250s was 1.4C, and from the 1650s~1670s to the 1740s~1760s was 1.2C.

In discussing the implications of these several observations of pre-20th-century faster-than-recent warming and higher-than-recent temperatures, Ge et al. say that their analysis "gives a different viewpoint from that 'the 20th century is the warmest century in the past 1000 years', presented by IPCC, and is of great significance for better understanding the phenomena of the greenhouse effect and global warming etc. induced by human activities."  And what would that "different viewpoint" be?  In the words of Ge et al., "the temperature of the 20th century in eastern China is still within the threshold of the variability of the last 2000 years," which observation clearly indicates that the Chinese data provide no evidence for the hypothesis that the eastern part of the country's 20th-century warming - or even a small part of it - was human-induced.

Sherwood, Keith and Craig Idso

Reference
Ge, Q., Zheng, J., Man, Z., Fang, X. and Zhang, P.  2004.  Key points on temperature change of the past 2000 years in China.  Progress in Natural Science 14: 730-737.