The summer of 2025 is shaping up to be one of the hottest on record in Japan. Across the country, temperatures are soaring to 38–39°C, and in Tokyo, consecutive days of extreme heat have already pushed daily highs well above 35°C. Experts warn that Tokyo hitting 40°C is no longer a question of “if,” but “when.”
In this article, we will examine the reasons behind this unprecedented heat, the dangers it poses, and what you can do to stay safe.
Record-Breaking Heat Across Japan
According to data from the Japan Meteorological Agency (JMA):
- Inland cities such as Saitama, Gunma, and Gifu have already approached 39°C.
- Tokyo has seen an unbroken streak of “extremely hot days” (35°C and above).
- Heatstroke-related emergency cases are up 20% compared to last year.
Even at night, temperatures remain high, resulting in tropical nights where it’s difficult to cool down, leading to widespread sleep deprivation and fatigue.
Why Is It So Hot This Year?
1. Global Warming
Rising global temperatures are intensifying Japan’s summer heat. The effects of climate change are particularly evident in urban environments.
2. Urban Heat Island Effect
In dense cities like Tokyo, heat is trapped by concrete and asphalt during the day and radiates at night, preventing temperatures from cooling down.
3. Persistent High-Pressure Systems
A stronger-than-usual Pacific high-pressure system has trapped hot air over Japan, causing a prolonged heatwave across the country.
The Dangers of “Life-Threatening” Heat
- Heatstroke Surge
Cases are not limited to outdoor activities; indoor heatstroke is also becoming alarmingly common, especially among the elderly and children. - Strain on Infrastructure
High temperatures are placing stress on power grids, rail systems, and other critical infrastructure, raising risks of blackouts and transportation delays. - Human Limits
Sustained exposure to 38–40°C heat can overwhelm the body’s ability to regulate temperature, leading to severe heatstroke, which can be fatal.
Is Tokyo Really Going to Hit 40°C?
Historically, Tokyo has recorded highs near 39.5°C, while nearby Saitama’s Kumagaya reached 41.1°C in 2018. Given this year’s extreme patterns and urban heat retention, experts believe that Tokyo surpassing 40°C is entirely plausible in the near future.
How to Protect Yourself
- Use Air Conditioning Effectively: Don’t hesitate to run your AC. Keeping indoor temperatures below 28°C is essential for safety.
- Stay Hydrated: Drink water and electrolytes frequently, even before you feel thirsty.
- Avoid Midday Outdoors: Plan outdoor activities for early morning or late evening.
- Cool Your Home: Use blackout curtains and fans to reduce indoor heat buildup.
- Look Out for Vulnerable People: Check in on elderly relatives, children, and neighbors.
When the government issues a Heatstroke Alert, avoid unnecessary outings—this can literally save lives.
Conclusion: 40°C Summers May Be the New Normal
A 40°C summer day in Tokyo is no longer a rare anomaly—it’s fast becoming a realistic scenario. Surviving this summer safely requires proactive, science-based heat measures rather than outdated “tough it out” approaches.
As climate change accelerates, we may be witnessing the dawn of a new normal: summers that pose genuine, life-threatening dangers if proper precautions aren’t taken.