What was done
An uninterrupted 1100-year history of March mean temperature at Kyoto, Japan, was developed from phenological data on the times of full-flowering of cherry trees (Prunus jamasakura) acquired from old diaries and chronicles written at Kyoto, which data were calibrated against instrumental temperature measurements obtained over the period 1881-2005, after which the results were compared with the sunspot number history developed by Solanki et al. (2004).

What was learned
Aono and Kazui say their results suggest "the existence of four cold periods, 1330-1350, 1520-1550, 1670-1700, and 1825-1830, during which periods the estimated March mean temperature was 4-5°C, about 3-4°C lower than the present normal temperature," and that "these cold periods coincided with the less extreme periods [of solar activity], known as the Wolf, Spoerer, Maunder, and Dalton minima, in the long-term solar variation cycle, which has a periodicity of 150-250 years." In addition, they report that "a time lag of about 15 years was detected in the climatic temperature response to short-term solar variation."

What it means
The results of this study comprise but one additional example of the findings of many investigations that have documented the significant effect of solar activity variability on earth's climate, as may be verified by perusing the materials we have archived under the general heading of Solar Effects (Centennial-Scale Cycles) in our Subject Index, as well as the materials we have posted under the many other sub-headings grouped beneath the "Solar Effects" umbrella.

Reference
Solanki, S.K., Usoskin, I.G., Kromer, B., Schussler, M. and Beer, J. 2004. Unusual activity of the Sun during recent decades compared to the previous 11,000 years. Nature 431: 1084-1087.