Japan announces new name for days over 40C after hottest summer ever

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🗞️ Driving the news: Japan has introduced a new meteorological term, “kokushobi”, to describe days when temperatures exceed 40°C, following the country’s hottest summer since records began

🔭 The context: The new classification was announced by the Japan Meteorological Agency after 203,000 people participated in a public vote to name the phenomenon
• “Kokushobi,” meaning “cruelly hot” or “brutally hot day,” will be used in weather forecasts to warn the public about dangerous heat conditions
• Japan recorded its hottest summer ever in 2025, with average nationwide temperatures 2.36°C above historical norms and extreme heat reaching 41.8°C in the city of Isesaki, the highest temperature ever recorded in the country
• The new term extends Japan’s heat classification system, which already includes labels for days above 25°C, 30°C and 35°C

🌍 Why it matters for the planet: The need for a new category of extreme heat reflects the accelerating impact of climate change
• Scientists link Japan’s rising temperatures partly to warming ocean waters around the archipelago, which trap heat and intensify weather extremes
• Increasing heatwaves threaten public health, strain infrastructure, disrupt outdoor work and highlight the urgency of reducing global greenhouse-gas emissions

💬 One quote: “Kokushobi” means a cruelly or brutally hot day. — Japan Meteorological Agency

📈 One stat: Japan experienced nine days above 40°C in summer 2025, compared with four such days in 2024

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