Japan has given a name to a new kind of suffering: kokushobi, the 'cruelly hot day,' a term coined only in April and already pressed into use by mid-July as three cities crossed 40 degrees Celsius and records fell across the archipelago. The naming is itself a kind of reckoning — an acknowledgment that the old vocabulary of heat no longer holds, that what was once extreme has become a threshold on the way to something worse. A nation historically attuned to seasonal ritual and collective discipline is now rewriting its dress codes, its farming practices, and its sporting traditions in real tim
Japan records first 'cruelly hot day' as heat extremes reshape daily life
At least two heat-related deaths recorded in recent days; heatstroke deaths exceeded 2,000 in 2024 with over 100,000 hospitalizations between May-September.
The heat is forcing a reckoning with how things have always been done
Mark
Why did Japan need a new word for hot days? Didn't they already have ways to describe extreme heat?
Mimi
They did, but the old system was built for a different climate. Moshobi—extremely hot days—meant anything above 35 degrees. That used to be rare enough to be a warning. Now it's routine. They needed a word for the truly dangerous threshold, the point where the heat itself becomes a public health emergency.
Mark
And that threshold is 40 degrees?
Mimi
Yes. It's the temperature at which the human body starts to fail in ways that are hard to recover from. They didn't pick it arbitrarily. It's the line where heat stops being uncomfortable and becomes lethal.
Mark
The story mentions farmers switching to avocados. That seems almost absurd—Japan growing avocados at scale?
Mimi
It's not absurd at all. It's survival. Rice has been the foundation of Japanese agriculture for centuries. But rice needs specific conditions, and those conditions are disappearing. Avocados thrive in heat. So farmers are making a choice: adapt the crop or watch yields collapse. It's happening quietly, but it's a fundamental shift.
Mark
What strikes me most is the office dress code change. Shorts in a Japanese office?
Mimi
It's a small thing on the surface, but it signals something larger. Japan's corporate culture is famously rigid. Changing the dress code isn't just about comfort—it's an admission that the old rules don't work anymore. The heat is forcing a reckoning with how things have always been done.
Mark
The study about school sports becoming unplayable by the 2060s—is that a real possibility?
Mimi
If emissions continue on the current path, yes. It's not hyperbole. They're not saying sports will be inconvenient. They're saying the heat will make outdoor activity genuinely dangerous for children. That's a future where an entire generation loses access to something that's been part of growing up in Japan.
The Pulse
- Japan's weather service coined 'kokushobi' in April as a warning for temperatures above 40°C — and was forced to deploy it within weeks as three cities breached that mark, two of them shattering all-time station records.
- At least two men died from the heat in recent days, and the toll is no anomaly: 2024 saw more than 2,000 heatstroke deaths and over 100,000 hospitalizations in a single summer season.
- The crisis is dismantling long-held cultural norms — Tokyo's governor has permitted shorts and trainers in offices, the sacred koshien baseball tournament has been split into morning and evening sessions, and rice farmers are trialing avocados.
- The acceleration is the most alarming signal: 2023 was the hottest year on record, then 2024 surpassed it, then 2025 surpassed them both — with summer temperatures now running 2.4 degrees above the three-decade average.
- Without steep emissions reductions, researchers project that outdoor school sports will be unplayable in Japan by the 2060s, marking a civilizational shift in what daily life under the sun can safely mean.
Japan has given a name to a new kind of suffering: kokushobi, the 'cruelly hot day,' a term coined only in April and already pressed into use by mid-July as three cities crossed 40 degrees Celsius and records fell across the archipelago. The naming is itself a kind of reckoning — an acknowledgment that the old vocabulary of heat no longer holds, that what was once extreme has become a threshold on the way to something worse. A nation historically attuned to seasonal ritual and collective discipline is now rewriting its dress codes, its farming practices, and its sporting traditions in real time, as the climate outpaces the language used to describe it.
Japan's weather service introduced a new word in April: kokushobi, meaning 'cruelly hot day,' reserved for temperatures above 40 degrees Celsius. It was designed as a warning. By mid-July, it was already in use.
On a Tuesday in July, three cities in central Japan crossed the 40-degree threshold. Gujo and Toyota both hit the mark — Toyota reaching 40.1 — while Tajimi matched it exactly. For Gujo and Toyota, these were the hottest days their stations had ever recorded. Across the country, 278 of Japan's 914 weather stations logged temperatures above 35 degrees, the level that had previously represented the highest tier of heat warning before the new terminology arrived.
The heat was already killing people. A man in his 40s collapsed and died on a street in Niigata prefecture the day before; a man in his 70s died in Kanagawa. In 2024, heatstroke deaths had exceeded 2,000 for the first time on record, with more than 100,000 hospitalizations between May and late September.
The crisis was remaking Japanese life in visible ways. Rice farmers began planting heat-tolerant varieties and experimenting with avocados — a crop with no commercial history in the country. The koshien high school baseball tournament, a cultural institution held each August, restructured its schedule in 2024 to split games into morning and evening sessions. In Tokyo, Governor Yuriko Koike announced that workers could wear shorts, polo shirts, and trainers on the hottest days — a striking break from Japan's formal corporate tradition, framed as part of the 'Cool Biz' initiative to ease pressure on the electricity grid.
The longer trajectory was starker still. A 2025 study projected that without major emissions reductions, outdoor school sports would become unplayable by the 2060s. Japan's average summer temperatures had risen 1.3 degrees Celsius over the past century, but the pace was quickening: 2023 was the hottest year since records began in 1898, then 2024 surpassed it, then 2025 surpassed them both — running 2.4 degrees above the previous three-decade average. On a single day in August 2025, a station in Gunma logged 41.8 degrees, a new national record.
Japan had found a word for what was happening. The harder work — of slowing it — remained.
Japan's weather service had a problem: the language itself was becoming obsolete. In April, they introduced a new word—kokushobi, meaning "cruelly hot day"—to describe temperatures above 40 degrees Celsius. It was meant to be a warning system for an increasingly dangerous climate. By mid-July, they had already needed to use it.
On a Tuesday in July, three cities in central Japan crossed that threshold. Gujo and Toyota both hit 40 degrees, with Toyota climbing to 40.1. Tajimi matched the mark. For Gujo and Toyota, these were not merely hot days—they were the hottest days their weather stations had ever recorded. Across the country, 278 of Japan's 914 weather stations registered temperatures above 35 degrees Celsius, a level previously called moshobi, or "extremely hot days," which had been the highest warning tier until the new terminology arrived.
The heat was already claiming lives. On the Monday before, a man in his 40s collapsed and died on a street in Sanjo, in Niigata prefecture. Another man, in his 70s, died in Kanagawa, southwest of Tokyo. Both deaths were attributed to the heat. These were not isolated incidents. In 2024, heatstroke deaths had topped 2,000 for the first time on record. Between May and late September of that year, more than 100,000 people had been hospitalized with heat-related illness, according to Japan's fire and disaster management agency.
The crisis was reshaping how Japan worked and lived. Rice farmers, watching yields decline and quality suffer in the oppressive temperatures, began planting heat-tolerant varieties and experimenting with crops like avocados that had never been grown at commercial scale in the country. The national high school baseball tournament, koshien, a cultural institution played each August, had been restructured since 2024 to split games into morning and evening sessions, a concession to the reality that players and spectators could no longer safely endure a full day in that heat.
In Tokyo's office towers, the dress code itself was loosening. Governor Yuriko Koike announced that workers could now wear shorts, polo shirts, and trainers to the office on the hottest days—a radical departure from Japan's traditionally formal corporate culture. The measure was part of the "Cool Biz" initiative, designed to reduce air-conditioning use and ease pressure on the electricity grid during peak demand. Previous years had already permitted the shedding of jackets and ties. This year's forecast made even shorts seem necessary.
The long view was grimmer still. A 2025 study by the National Institute for Environmental Studies and Waseda University found that without drastic reductions in greenhouse gas emissions, outdoor school sports would become unplayable by the 2060s. Over the past century, Japan's average summer temperatures had risen 1.3 degrees Celsius. But the acceleration was quickening. Both 2023 and 2024 had been the hottest years since records began in 1898—until 2025 surpassed them both. That summer had been 2.4 degrees above the average of the previous three decades. One hundred thirty-two weather stations recorded their highest average temperatures ever. On August 5, 2025, a station in Isesaki, Gunma, north of Tokyo, logged 41.8 degrees Celsius, a new national record.
Japan had named the heat. Now it was racing to adapt to it.
Notable Quotes
Tokyo governor Yuriko Koike announced new clothing recommendations for office wear including shorts, polo shirts, T-shirts and trainers, citing expected high temperatures and a challenging electricity supply outlook.— Tokyo Governor Yuriko Koike
Want the full story?
Read the original at The Guardian ↗
General News