Since time immemorial, the city of Kyoto in Japan has been famous for its hanami, or cherry blossom viewing. Each year, between April and May, the trees in the ancient city burst into bloom, attracting sightseers from all over the world to witness what is traditionally regarded as an iconic herald of spring.
But thanks to climate change, spring is coming earlier and earlier these days. According to a new study published in the IOP journal Environmental Research Letters, the cherry blossoms in Kyoto are blossoming a full 11 days earlier than they would without the effects of human-driven climate change – and extremely early flowering dates are now 15 times more likely than they would otherwise be.
“Not only have human-induced climate change and urban warming already impacted the flowering dates of cherry blossom in Kyoto,” said Nikos Christidis, lead author of the paper and a climate scientist with the UK’s Met Office, “but … extremely early flowering dates, as in 2021, are now … expected to occur at least once a century.”
Last year the cherry blossoms flowered by a record March 26, the earliest in over 1,000 years This year the trees reached full bloom by April 1.
Although the tradition of cherry blossom viewing stretches back more than 1,200 years, there’s actually solid science behind the idea of the flowers signaling spring. Cherry blossoms don’t flower unless the temperature has been warm enough to trigger it for multiple days in a row – it’s a clever way to get around those random heatwave days you sometimes see in January that might otherwise leave a tree trying to germinate in snow. Usually, that temperature is reached in Kyoto starting from March, when the city reaches about 9-10°C – but without human influence, Christidis told New Scientist, it would be closer to 5-6°C.
“This information has been found in all sorts of sources like emperor’s recordings,” Christidis told New Scientist. “The blooming of cherry blossoms in Kyoto has been an important event in Japan since ancient times.”
Climate change has shifted the cherry blossom’s debut up by about six days, the research shows, but it isn’t the only human-made issue that’s bumping up the blossoming. As cities industrialize and grow, they become warmer – it’s a result of man-made things like roads not absorbing sunlight as effectively as, say, grass, as well as all that waste energy from things like fridges and AC units. In Kyoto’s case, those warmer temperatures are causing the cherry blossom to bloom a further five days earlier than they would outside a city, which the team confirmed by comparing temperatures recorded from a weather station in the center of Kyoto and from a station in the rural location of Kameoka.
If greenhouse gas emissions continue as they are, the team found, then those 11 days total – six from climate change and five from urbanization – will increase further by nearly another week.
“[Early flowering] events are projected to occur every few years by 2100 when they would no longer be considered extreme,” noted Christidis.