Kitagawa, H. and Matsumoto, E. 1995. Climatic implications of δ13C variations in a Japanese cedar (Cryptomeria japonica) during the last two millennia. Geophysical Research Letters 22: 2155-2158.
What was done
The authors analyzed δ13C variations of Japanese cedars growing on Yakushima Island, southern Japan (30°20'N, 130°30'E), in an effort to reconstruct a high-resolution proxy temperature record over the past two thousand years. In addition, they applied spectral analysis to the δ13C time series in an effort to learn if any significant periodicities were present in the record.
What was learned
Significant decadal to centennial-scale variability was noted throughout the record, with temperatures fluctuating by about 5°C across the series. Most notable among the fluctuations were multi-century warm and cold epochs. Between AD 700-1200, for example, there was about a 1°C rise in average temperature (pre-1850 average), which the authors state "appears to be related to the 'Medieval Warm Period'." In contrast, temperatures were about 2°C below the long-term pre-1850 average during the multi-century Little Ice Age that occurred between AD 1580 and 1700. Kitagawa and Matsumoto also report finding significant temperature periodicities of 187, 89, 70, 55 and 44 years. Noting that the 187-year cycle closely corresponds to the well-known Suess cycle of solar activity and that the 89-year cycle compares well with the Gleissberg solar cycle, they conclude that their findings provide further support for a sun-climate relationship.
What it means
The results of this study add to the growing body of evidence that the Medieval Warm Period and Little Ice Age were global phenomena. What is more, they indicate there is nothing unprecedented about Current Warm Period temperatures in this region, which according to the data presented in the authors' Figure 3, remain about a degree Celsius lower than the peak warmth of the Medieval Warm Period.