TOKYO — Travelers who arrived in Tokyo in April 2023 to experience the city's famous cherry tree petals were faced with quite a surprise: instead of blooming as forecast in late March, the pink sakura appeared 10 days earlier than predicted.

This was no freak occurrence: 2023 tied with 2020 and 2021 for a record-early bloom – the definitive earliest since scientific records began in 1953, and earliest since 812, according to historical documents from Kyoto. According to experts, this trend points to a troublesome fact: we are overheating our planet at a frightening pace, and the early sakura are harbingers of more change to come.

Japan's beloved four seasons are under threat altogether, says Yoshihiro Tachibana, professor of Climate and Ecosystem Dynamics from Japan's Mie University. "If greenhouse gas reductions cannot be achieved, there is the possibility of cherry blossoms in February. All four seasons are warming. But spring warming is seeing the biggest rise, so the cherry blossom season tends to come earlier and earlier."

This year, some forecast a start to the sakura season on par with the earliest recorded blooms, around March 25. But when, exactly, the sacred blooms might appear is really anyone's guess.

Early cherry blossom season in Japan may be annoying for the plan-ahead traveler, but it's also drama that transfixes the nation as Japanese people eagerly eye what's known as the "cherry blossom front". This chart plots the progress daily of the advancing pink flowers across the Japanese archipelago from the south. Such a predictable line of blossoms is only possible owing to the nation's predilection for one particular cherry, the Yoshino. Clones of a single (UK) specimen account for 90 percent of the sakura cultivar in Japan.

Japan has come to be associated with this tree's tell-tale stirring drifts of powder pink. They're a sight on many travelers' bucket lists, but given their fleeting appearance of an ever-shifting 11-day window, guaranteeing a viewing is becoming increasingly fraught for international visitors.

It's important to note that the timing of the peak cherry blossom viewing varies from year to year depending on the weather. If the weather in the preceding weeks is warm, the blossoms will open early.

"Spring warming is the most important determinant of flowering times for cherry trees," said Richard B. Primack, a researcher and professor of biology at Boston University whose lab focuses on how climate change affects the timing of seasonal biological events. "And because spring weather is getting warmer, cherry trees are flowering earlier. "

According to Primack, sakura's flowering times have been recorded across Japan for hundreds of years, making them among the best-documented examples of the biological effects of climate change in the world.

"Yoshino cherries are now flowering about two weeks earlier than they did 50 to 60 years ago, and this is due to the warmer weather associated with climate change," Primack said.

Should travelers find themselves caught out by the shifting sakura, it's important to be flexible in your itinerary. Arrive too late for peak blooms in Tokyo or Kyoto? Try heading north to be sure of catching some: The latest you can witness the petals in Japan is in Hokkaido in May. Fancy an early spring bloom viewing? Then scamper off to semi-tropical Okinawa in January.

Since the progress of the cherries is followed so enthusiastically in Japan, researchers hope such abrupt changes to these phenological events will raise public awareness of the impact of climate change – and encourage citizens to act.

But when it comes to addressing climate change Japan has a long way to go, says Hanna Hakko, a senior associate at E3G, an independent climate change think tank in Tokyo

"Japan is currently facing significant challenges in meeting its mid-term and 2050 climate targets," she said. "Several analyses indicate that Japan is falling short in replacing fossil fuels with clean energy, especially in the power sector. Both the government and private sectors need to intensify their efforts by implementing policies and increasing investments to retire coal plants, expand renewable energy, and enhance energy efficiency."

The country has been the repeated recipient of the satirical "Fossil of the Day" award — which the Climate Action Network-International (CAN) gives out — at the annual COP conference. The awards are given to the countries who are behind the times when it comes to climate action.

With the recent building of new coal-fired power stations, in many ways, Japan's energy policies are backwards-looking approaches to the nation's green efforts.

James Hollow, founder of Tokyo's Fabric consultancy, which conducts an annual "Sustainability in Japan" study, said we shouldn’t be surprised that "climate consciousness levels are still very low in Japan".

"Climate change has not been politicized as it has elsewhere. Citizens expect government to take the lead. While activism around climate and social issues is limited," he said. "But, climate consciousness levels are trending up significantly."

Japan is becoming acutely aware that not just the spring weather is shifting, but that all seasons are out of kilter. Summers in Japan's largely concrete cities are becoming unbearably warm and humid for longer, delaying the arrival of cooler autumn weather in the process.

"Summers will become so intolerable even the most hardy foreign tourists will cease to visit," said Prof Tachibana.

Perhaps the sight of a February sakura front — and summers bereft of tourists who are now evading Tokyo and Kyoto's soupy 50C (122F) heat — will serve as a motivator for Japan to rethink its approach to the climate crisis. Because without more effective climate action, those cherished four seasons will become just a memory for travelers and locals alike. — BBC