Before There Was a Word: When the Meteorological Agency Finally Named Extreme Heat

On April 18, Japan’s Meteorological Agency officially defined days with maximum temperatures of 40°C or above as ’koushutsubi’ (extreme heat day). On the surface, this appears to be a technical bureaucratic decision—a simple matter of categorizing meteorological data. Yet I find myself, in the face of this announcement, gripped by something that might be called anger. Though perhaps what I feel is colder than anger.

Because the 40°C day did not appear yesterday or today. If we trace back through Japan’s meteorological observation history, days exceeding 40°C began appearing in the early 2000s. In 2007, Takayama in Gifu Prefecture recorded the highest temperature in observation history: 40.9°C. For nearly twenty years since then, this meteorological phenomenon has existed. Yet until now, it lacked an official definition from the Meteorological Agency. In institutional terms, it was non-existent. Meanwhile, the people working outdoors lived through those 40°C days in their bodies. Society simply continued without the words to name it.

Until a phenomenon finds words, it remains invisible to institutional eyes. This simple reality makes me pause and ask: what does this mean?

According to the Meteorological Agency’s announcement, the definition of ’koushutsubi’ is straightforward: “a day when the daily maximum temperature reaches 40°C or above.“ It will be added as a category alongside the existing ’manatsubi’ (days of 30°C+) and ’moushobi’ (days of 35°C+). The agency’s decision appears to have been accelerated by the record temperatures observed throughout Japan’s 2024 summer. Or more accurately, the reality is that days exceeding 40°C have become so frequent that they can no longer be ignored.

This institutionalization carries a small measure of progress. The criteria for meteorological warnings may shift. Public health offices and labor standard bureaus will gain clearer benchmarks for policy decisions. Schools’ decisions about suspending outdoor club activities and the parameters for outdoor labor safety will become more concrete. Media outlets, armed with an official term, can communicate the danger more effectively. Words carry power—the power to make societies see and recognize.

Yet what does this “finally, now“ moment tell us? For nearly two decades since 2007, the 40°C day existed as lived reality. In agricultural fields, everyone understood that flower buds risked damage during such periods. In construction sites and courier services, workers had to devise their own safety protocols because official ones didn’t exist. Power grids have operated at full capacity to meet surging air-conditioning demand. Housing manufacturers began realizing that conventional insulation standards were becoming inadequate. The present was already here. Society simply lacked language for it.

Construction workers sweating in the sun, farmers standing in blazing fields, delivery drivers in their trucks—they were already living in the 40°C world. They endured that reality in a state where it was, officially, non-existent. Workplace injury statistics recorded “heat-related illness“ without noting that the thermometer had crossed 40°C. The official record did not acknowledge the temperature’s true magnitude.

With the Meteorological Agency finally providing a word, future decisions like “outdoor work must not occur on extreme heat days“ will carry stronger institutional weight. That development is not unwelcome. It is, in fact, necessary. But I cannot remain silent about the length of time during which countless individuals endured those 40°C days alone, waiting for society to catch up to their experience.

Japan’s electrical infrastructure is already being redesigned around the assumption of 40°C. Each summer will break records for air-conditioning demand. Power supply constraints are no longer exceptional news. Electricity companies navigate a precarious balance between transitioning to renewable energy and maintaining fossil fuel capacity. Between the national goal of cutting greenhouse gases by 46% by 2030 and the immediate physical reality of 40°C heat, every option feels insufficient. The pressure accumulates quietly.

To avoid blackouts, conservation appeals will be issued. Yet the request “use no air conditioning when temperatures exceed 40°C“ lacks any legitimate foundation. The human body, at that temperature, cannot survive without cooling. This is not an ethical dilemma—it is a physical fact. The supply side cannot demand that the demand side endure the unbearable; it must build adequate infrastructure. There is no choice but to meet the need.

In agriculture, the changes wrought by 40°C are already visible. High-temperature damage to rice crops is now reported nationwide. The same paddies, with the same varieties, no longer produce the quality yields of previous decades in certain regions. Farmers have begun considering switching crop varieties. In traditionally cooler regions like Hokkaido and the Tohoku area, rice cultivation is actually improving, and acreage is expanding. Japan’s agricultural map is being quietly redrawn. The 40°C temperature threshold has become inseparable from food security.

Climate adaptation must proceed industry by industry. Rice farming operates in short cycles, allowing relatively rapid variety trials and replanting decisions. But what of fruit cultivation? Apple, grape, and pear orchards require years—sometimes decades—before yielding harvests. Beginning a variety transition today yields results only years hence. As northern cultivation limits shift northward, continuing traditional farming in legacy growing regions means gradually losing economic viability. Japan’s declining agricultural population means fewer people remain to make these critical adaptation decisions each passing year.

The housing industry has reached a stage where climate change can no longer be ignored in design. Conventional Japanese building standards prioritized winter warmth retention in cold regions. Now, summer heat poses an equally formidable—or greater—design challenge. New residential building standards are incrementally strengthening insulation requirements. Yet what of the existing housing stock? Most of Japan’s homes were constructed without anticipating a 40°C climate. Renovation and performance upgrades are technically possible, but economically burdensome for most homeowners.

What results? As 40°C days proliferate, air conditioning transitions from “luxury“ to “survival necessity.“ Electricity becomes a non-discretionary expense. As households increasingly depend on private cooling solutions to offset climate deterioration, energy poverty risks rise. Elderly and low-income households may economize on cooling costs, enduring dangerous heat instead. This structure will become starkly visible.

What happens next, now that the Meteorological Agency has provided the word ’koushutsubi’? Policy makers across government agencies will likely begin constructing more explicit standards on this foundation. Labor law interpretations may shift. Building code thermal performance standards will almost certainly tighten further. Agricultural policy may develop new classifications: “regions experiencing X or more extreme heat days.“

Yet these are all reactions to what has already occurred. Reality moves faster than definitions. The human body working outdoors at 40°C cannot wait for bureaucratic terminology. Crops wither before official language exists. Power grids have already been preparing for demand surges long before the Meteorological Agency named the phenomenon.

I return to the coldness of it all. How much reality accumulates while institutions deliberate before recognizing? Without words, there are no statistics. Without statistics, policies lack urgency. Without urgency, responses delay. And while responses delay, individuals suffer in isolation, their experiences uncounted. Is this simply how society functions?

The Meteorological Agency’s decision marks Japan’s official entry into the 40°C era. It is not a bad decision. It is a necessary one. But why now? Why did it take until now to arrive here? That question will not fade.

How will Japan live with days of 40°C and beyond? How will it secure power, grow food, design homes? The answers can no longer wait. On these questions, I will watch closely—observing how reality changes after the words are finally spoken.