For over a thousand years, the blooming of cherry blossoms has been a key event of the year in Japan, celebrated by huge crowds. Celebrated, and recorded.

Yasuyuki Aono, a researcher from Osaka Prefecture University, has collected records of the annual sakura (cherry blossoms) bloom from primary sources going back as far as 812 AD. Scouring historical documents and even personal diaries from people living in Kyoto, Aono charted the peak blooming period in that particular location for over 1,200 years.

For most of that time, the peak bloom was recorded as being in mid-to-late April, with rare early spikes as early as March 28. Once, in the early 1400s, it happened on March 27. In the 1900s, the rolling average date began to move earlier; it is currently April 6.

But in 2021, a new record was set. For the first known time, the bloom of cherry blossoms in Kyoto reached their peak on March 26. And that’s worrisome.

“Sakura blooms are very temperature sensitive,” said Aono. “Flowering and full bloom could be earlier or later depending on the temperature alone. The temperature was low in the 1820s, but it has risen by about 3.5 degrees Celsius (6.3 degrees Fahrenheit) to this day.”

Climate change is partially the cause of this – it certainly played a part in Japan’s very cold 2020-21 winter, followed by the unusually fast and warm spring. The other aspect is Kyoto itself, where increased urbanization causes a “heat island effect,” or a bubble of heat caused by all of the paving and industry of the city.

While flowers blooming a few days early may not seem important, the context is massive. Ecosystems operate in long-built relationships – the flowers blooming too early may mean that the insects which have evolved to pollinate them aren’t awake yet, meaning the trees may wind up unable to produce fruit this year, which will then starve whatever niche was waiting for that fruit, and so the effect tumbles uphill along the food chain.

Photo: cherry blossoms at the Shinto shrine of Fushimi Inari Taisha near Kyoto, Japan. Credit: Shutterstock