When I learned that the time of autumn color has shifted at later date since Heian period, I wondered if global warming began far before the current climate change due to greenhouse gas emission. But the time of cherry blossom shows a different trend from autumn color. The data are abundant for cherry blossom. They were collected from the diaries and chronicles written by ancient aristocrats and monks. According to these data the peak times of cherry blossom fluctuate from year to year within a range of about 10 days. But when the peak date was plotted against year from 9th century to the present, the curve for the middle value shows that the peak time did not shift much up to 1800 and then moved sharply to earlier date. This curve is in accordance with that of global warming due to green house gas emission.
Cherry blossom is closely connected to Japanese cultures and traditions. Entrance ceremonies of companies and schools have been held at its peak season. But soon we will see such ceremonies held after cherry flower has gone.
