Why Japan is experiencing a record heat wave

The current record heatwave in Japan is the result of the interaction of climate change, anomalous barometric conditions, extreme temperatures and humidity, an aging population and some limitations in the ability to adapt quickly.

The number of hospitalizations for heatstroke exceeding the ceiling is therefore not only unusual, but also a clear warning of the need to cope with increasingly severe climate extremes. The reason why Japan is experiencing a record heatwave and more than 10,800 people have been hospitalized in one week is due to a combination of adverse climate factors – especially climate change and extreme weather events. 

During the week of July 21 to 27, 2025, there were 10,804 hospitalizations for heatstroke and heat exhaustion, and 16 deaths were recorded. 

The highest temperature recorded was 41.2°C in Tamba, Hyōgo Prefecture, surpassing the national record from 2020 and 2018.

More than 322 out of 914 stations nationwide recorded temperatures ≥35°C, the most since 2010.

Main causes.

Extremely high temperatures and high humidity

Not only did the temperature rise, but the high humidity also made it feel “much hotter than it actually is”. The WBGT (a combination of temperature, humidity, wind, and solar radiation) could exceed the threshold that is dangerous for health, especially for the elderly and outdoor workers.

Climate change.

Japanese and international climatologists assert that this heat wave would have been almost impossible without the impact of human-caused climate change.  Current weather conditions – such as the unusual temperatures in mid-June – are a clear example.

Stable high pressure.

A largely stable high pressure system over the North Pacific has pulled hot air from the tropics into Japan, causing a prolonged “heat dome” (similar to previous extreme heat waves, especially in 2022).

Aging population and lack of adequate air conditioning

Japan has an aging population – 60% of hospital admissions were for people over 65, with 17,229 people hospitalized for heatstroke in June alone (nippon.com). Many of these cases occurred in homes where air conditioning was not turned on or not used properly.

Why are hospital admissions rising past 10,000/week?

Extremely high temperatures and humidity dehydrate the body quickly, especially in heat above 40°C.

The number of stations recording ≥35°C is at its highest since 2010, spreading across the country.

The prolonged hot weather has caused people, especially the elderly, to be physiologically overloaded.

The heat dome phenomenon and climate change have increased the frequency and intensity of heat waves compared to before.

Heat control and prevention measures

The Japanese government has encouraged the use of air conditioning, fans, and adequate water intake, not saving energy at the expense of health.

Outdoor labor protection regulations: Monitor environmental conditions (WBGT) and workers' health status when temperatures exceed 31°C.

Outdoor sports activities (such as schools, tournaments) have changed schedules, increased breaks between matches, moved to the morning or late afternoon, and even used the option of competing in colder regions.

Element Description Extreme temperatures Recorded up to 41.2°C, easily causing heatstroke and exhaustion High humidity Increases the heat effect many times Climate change Increases the frequency and intensity of heat waves Heat dome Stable high pressure maintains temperature and humidity for many days Aging population & lack of cold storage Vulnerable groups are often unable to protect themselves.