TOKYO — The weather agency inspectors had fanned out to examine designated trees across Japan, eyeballing the branches, looking for blossoms. Government computers had crunched years of temperature data. TV camera crews climbed ladders to get close-ups of the buds' progress.
On Tuesday, inspectors in Tokyo saw what everyone was waiting for: at least six cherry blossoms on one of the talismanic trees on the grounds of sacred Yasukuni Shrine. They proclaimed sakura season officially underway.
Early again. As usual.
The beginning of sakura has been creeping up on the Japanese in recent years. This year's start was eight days earlier than the average in Tokyo over the last half a century, part of a pattern that many scientists here attribute to global warming.
Climate change "would contribute to the speeding up of the flowering," says Hiroshi Nagata, professor emeritus of Mie University who has been studying trees for 40 years and says the season is undeniably starting earlier.
Warmer temperatures are also changing the distribution of the species, he says, noting that the habitat of the somei yoshino species that is identified with cities such as Tokyo and Kyoto may be retreating northward, to the colder climate it needs to blossom.
For well over a millennium, the Japanese have made a sport of their collective anticipation of the annual explosion of pink and white sakura blossoms that marks the arrival of spring. The moment is more spiritual than botanical. The cherry blossom is a symbol of Japanese identity. The petal's 10-day span from glorious youth to wilting and inevitable death is seen as a metaphor for life's swift passage.
It is also an excuse for executives, students and stay-at-home moms to ditch work and throw daylong parties of singing and drinking under canopies of petals.
The sakura once bloomed in a monthlong wave that spread northward, culminating on the chilly island of Hokkaido. Their progress was tracked, informally for centuries -- and since 1953 by the scientists at the Japan Meteorological Agency -- with a care and concern normally reserved for the movement of typhoons.
But the official advent of sakura has moved up by 4.2 days since records started to be collected, Japan's Environmental Agency says. And the blossoms are coming out even earlier in the big cities, regardless of latitude: 6.1 days earlier in the six largest urban areas, according to the agency's data.
Tokyo saw the nation's first blossoms this year -- at least as officially noted by the inspectors. The city of Fukuoka followed a day later, earlier than rural parts of the southern island of Kyushu.
Scientists say that's because the concentration of high-carbon fuel use in big cities makes urban temperatures higher than in the countryside.
"The pattern of recent years has seen the sakura flower in cities for two reasons: because of global warming and because of the heat island phenomenon," says Keiko Masuda, a climatology professor at Ryukoku University in Kyoto.
Naturalists and scientists say more than just sakura is changing. The seasons for rice planting and tea-leaf picking are also coming earlier in the calendar year because of milder winters, they say. And Nagasaki's swallowtail butterfly has been observed in northern Japan. At least 12 other butterfly species have migrated with the changes in temperature, according to scientists.
Where the butterflies go, the plants will follow, Nagata says.
Those changes are causing havoc for the travel business, for which sakura is one of the busiest times: Thousands of Japanese seek out prime spots to ogle and snap pictures of the spectacular blossoms. A less predictable season makes it harder to organize bookings. Some municipalities have tried to stave off the blooming season by packing snow around the trees in an attempt to fool them into thinking warmer temperatures have yet to arrive. So far, it hasn't worked.
But to many Japanese, the scientific implications are secondary to the potential crimp an earlier cherry blossom season puts in their social agenda. Sakura has always coincided with the interval between Japanese school years and the end of the corporate fiscal year. Sighting the blossoms has been the pistol shot for this tightly wound society to loosen its tie and party a bit, even in the middle of a workday.
So a warming planet means more to Japan than just an earlier arrival of spring. It means an earlier start to spring fever.
Hisako Ueno of The Times' Tokyo Bureau contributed to this report.