Japan's average temperature in July reaches a record high for the third consecutive year, 2.89°C above the normal, indicating a "normalization of extreme heat."

1. What Happened: The Impact of "2.89°C Higher"

• Fact: In July 2025, Japan's average temperature exceeded the normal (30-year average from 1991–2020) by 2.89°C, marking the third consecutive year of record-breaking July temperatures. This is the highest since comparable statistics began in 1898, surpassing the previous record in 2024 (+2.16°C). This indicates not just a single year of "extreme heat," but the normalization of extreme heat. (Japan Today)
  
  

• Signals During the Same Period: Across Japan, days with temperatures above 35°C, known as extreme heat days, occurred frequently, leading to record levels of heatstroke hospitalizations on a weekly basis. In the last week of July, 10,804 people were transported by ambulance, marking the highest number this year. In urban areas, nighttime temperatures remained high, resulting in consecutive tropical nights and "record-breaking hot nights." (The Japan Timesguyonclimate.com)
  
  

• International Context: Several Asian countries also faced extreme heat, with Japan and South Korea experiencing record high temperatures simultaneously at the end of July. The unprecedented nighttime high temperatures are increasing health risks. (The Guardian)
  
  

2. Why Is It So Hot? — Complex Factors of Climate and Weather

1. Long-term Trend of Global Warming
   According to integrated reports of observation and evaluation, Japan's average temperature is expected to rise further towards the end of this century, with scenarios indicating greater increases at higher latitudes. This is due to the increase in greenhouse gases and the resulting changes in atmospheric and oceanic circulation. (Japan Meteorological Agency Data)
   
   

2. Persistently High Sea Surface Temperatures (SST)
   In recent years, sea surface temperatures around Japan have remained higher than normal, serving as a source of warm air in the summer. In June 2025, high SSTs were observed on the Pacific side as well. (The validity of this assumption is based on general knowledge from JMA's monthly reports and bulletins)
   
   

3. Strengthening and Expansion of the North Pacific High
   From around the end of the rainy season, its influence strengthened near Honshu, leading to increased instances of clear skies and suppression of nighttime radiative cooling due to phenomena like the foehn effect. This is similar to the situation during the heatwave of 2024. (General meteorological explanation)
   
   

4. Urban Heat Island
   Due to paving and high-density buildings, nighttime heat release is hindered, increasing the frequency of tropical nights. Even with the same rise in outdoor temperature, the perceived heat load (heat index) is significantly higher in urban areas. (Refer to the Ministry of the Environment's WBGT guidance) (WBGT Information SiteWBGT Information Site)
   
   

3. "Dangerous Heat" Viewed by Region and Time of Day

• Daytime (12–16): The combination of rising temperatures, strong sunlight, and low wind speeds frequently pushes outdoor work, club activities, and events into the WBGT "danger" zone. Planned breaks, cooling, and setting work stoppage lines are essential. (WBGT Information Site)
  
  

• Evening to Night: High temperatures and humidity persist, leading to discomfort and decreased sleep quality, which can result in chronic fatigue and impaired judgment. Recently, there is a need to shift the perception to **"the hottest time is at night."** (The Guardian)
  
  

4. Impact on Society: Health, Power, Economy, Education, Sports

4-1. Health Impact

• Surge in Emergency Transport: In late July 2025, 10,804 people were transported by ambulance in one week. Risks are concentrated among the elderly, those with underlying conditions, and outdoor workers. Establishing cooling shelters and community watch systems is urgently needed. (The Japan Times)

• Nighttime Heat and Chronic Risks: The increase in tropical nights burdens cardiovascular and kidney functions and raises the risk of accidents due to sleep deprivation. WBGT should be referenced not only during the day but also indoors, and if fans are insufficient, appropriate use of air conditioning is recommended. (WBGT Information Site)

4-2. Power Supply and Demand

• The surge in cooling demand leads to power shortages during peak times, exposing vulnerabilities in regions and households. In the medium to long term, a shift in power supply composition and enhanced energy conservation are simultaneously required. (Referencing OCCTO-related information) (Japan Beyond Coal Zero Coal-Fired Power Plants by 2030)

4-3. Economy and Industry

• Agriculture: High temperatures lead to an increase in immature white grains in rice, sunburn on fruit, delayed growth, and reduced quality in vegetables. Fluctuations in yield affect prices.

• Tourism: Extreme heat shifts outdoor tourism activities to morning and evening, with a tendency for indoor and waterside attractions to be more crowded during the day. In popular tourist destinations like Kyoto, multilingual heatstroke prevention measures are essential. (The Guardian)

• Work Safety: In workplaces with a high outdoor component, such as construction, logistics, and agriculture, it is necessary to formalize **work stoppage criteria (WBGT)** and provide cooling vests and moisture-wicking clothing.

4-4. Education and Sports

• According to research institution estimates, by around 2065, the time periods when most outdoor sports can be safely conducted during the summer will be reduced. Adjustments to game times are already underway for national high school baseball tournaments. Shifting club activities to early morning, evening, or indoors is key. (The Times)
  
  

5. Scientific Use of the "Heat Index (WBGT)"

• What is WBGT: A comprehensive index of temperature, humidity, solar radiation, and wind. It is the world standard for safety management in labor and exercise based on ISO 7243.
  
  
  

• Guidelines for Action:

  • Danger (31°C and above): Principally cancel activities / prohibit outdoor exercise.

  • Severe Warning (28–31°C): Frequent breaks, hydration with electrolytes, avoid strenuous exercise.

  • Warning (25–28°C): Regular hydration, stop activities for those feeling unwell.

  • Caution (21–25°C): Take breaks and hydrate as needed.
    *Values are from the Ministry of the Environment's guidance (regional differences apply). (WBGT Information SiteWBGT Information Site)
    
    
    

• Practical Tips:

  1. Link with municipal heat warning alerts and review "cancellation criteria" in schools and workplaces.

  2. Check nighttime WBGT and adjust bedroom temperature and humidity to **24–27°C with 50–60% humidity** using air conditioning.

  3. For the elderly,