Global warming: Japan is fighting heat death with low and high tech

Heat waves are an issue everywhere. Japan’s government now wants to reduce heat deaths to zero. At the same time, companies sense new business.

(Image: Dmitry Rukhlenko /

An unprecedented heat wave in June not only made Tokyo’s power producer Tepco sweat. Nine extremely hot days in a row – with maximum temperatures above 35 degrees Celsius according to the Japanese definition – brought the world’s largest megacity to the brink of power blackouts. This is because the energy requirement has skyrocketed as a result of air conditioning. But even the increased artificial cooling did not help some of the sweating residents: the number of patients who suffered heat strokes rose to new records for this time. Over 14,000 cases were reported in the week following June 27.

For Japan’s Ministry of the Environment, this figure is a setback. It has issued the official goal of reducing the number of heat deaths to zero – at least in the long term. In recent years, the number has risen to over 1,500 victims per year. The government is trying to sensitize its citizens to the pitfalls of tropical summers.

Long before the effects of climate change, Japan was not only hot but also muggy between July and September. In the current heat wave, however, the maximum temperatures rose to over 40 degrees in several places – values ​​​​that the Japanese have never known in this mass. But there is one difference to Germany that makes the heat even more unbearable: It cools down even less at night. The nightly lows are often over 26 or even 28 degrees and thus in the range that used to be called midsummer.

To make matters worse, most areas of Tokyo resemble treeless concrete deserts that heat up particularly quickly. The waste heat from tens of millions of air conditioners is added to this. According to a Japanese industry association, 10.5 million air conditioners were sold in Japan in 2018, around 50 percent more than in all of Europe and per capita of the 126 million Japanese, significantly more than in the USA or China. The heat has therefore made the Japanese inventive for a long time: On the one hand, the manufacturers have massively enlarged the heat exchangers in the air conditioning systems in order to reduce power consumption. On the other hand, attempts are being made to cool bodies in public spaces using both low and high tech.

In the meantime, for example, a fashion has developed for men’s parasols, which provide portable shade in the high-rise canyons of the metropolis. Meanwhile, the traditional fan is increasingly being replaced by small, portable fans. Water is poured onto the street to create evaporative coolness; there are systems that spray water mist, which is also known in southern Europe.

In addition, vests, in which fans ensure a constant flow of air on the upper body, became widespread, first among construction workers and now more and more among ordinary people. At Sony, there is even a noble variant of the idea for over 100 euros, which promises relief for all four seasons – including heating.

Reon Pocket is the name of the device that wearers can wear in special shirts with pockets or with a special holder under the shirt collar between the shoulder blades. A metal plate cools the neck area in summer and warms it in winter. And of course, the bonsai air conditioner can be controlled with a smartphone app.

However, the current technological adaptations are no longer sufficient, says the government. In 2021, the Ministry of the Environment introduced a warning system against heat stroke. It is not based on the expected maximum temperatures, but on the “Global Cooling Limit Temperature” (WBGT). This term describes the coolest temperature that can be reached in a place through evaporation. In concrete terms, this means that the danger threshold for the human body’s cooling system changes with humidity. Because: 30 degrees with high humidity is riskier than 30 degrees in a dry climate.

The highest warning level “Danger, stop physical activity” is issued with a WBGT value of more than 31. In Japan, this roughly corresponds to temperatures of more than 35 degrees. Between 31 and 35 degrees, a “serious warning” is then issued on normally muggy days, with the request to refrain from heavy physical exertion.

The recommendations are then disseminated across the country through various channels. The weather office, the Ministry of the Environment, but also TV stations provide information about which hours of the day are particularly dangerous with daily temperature profiles. In the news of the public service broadcaster NHK, even the weather report with colorful pictures warns of the heat as well as the flight of pine and cedar pollen, which causes tens of millions of Japanese to sneeze.

But education is still needed to meet the official target of zero heat deaths, especially among Japan’s rapidly growing elderly population, which is particularly vulnerable to heat as it ages. The seniors are used to “gaman”, i.e. to struggle through suffering without complaint and not giving up. So there are still people who don’t turn on the air conditioners and then die in their homes.

Japan’s insurers, on the other hand, are beginning to turn inevitable climate change into a business. Several insurance companies now offer insurance against heat stroke, some of which cover the costs of subsequent treatment.


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