Isn't 2025 Just About Temperature? The Real Nature of a Humidity-Choked Summer
"Isn't It Suffocating This Summer?"
The temperature is of course high. But more than that, many people are saying "I can't sweat," "the wind doesn't cool me down," and "it's stuffy even at night."
The reason is the abnormally high humidity in 2025.
This article explains, in plain language, why the summer of 2025 may feel more oppressive than the thermometer suggests.
The "Experience" of Heat Is Not Determined by Temperature Alone
The "heat" we feel is not determined by the temperature alone.
High humidity prevents sweat from evaporating and prevents body temperature from dropping.
The combination leads to:
- Body heat stays trapped instead of dissipating
- Sweating accelerates, increasing the risk of dehydration
- Heatstroke risk surges
In other words, "35°C and crisp heat" is often easier than 31°C with 80% humidity - the latter places a heavier burden on the body.
2025 Delivers a Double Punch: Temperature + Humidity
This year's feature is that the temperature is high but the humidity is also high.
Take Osaka in July 2025 as an example:
- Average temperature: 31.6°C (+1.3°C year-over-year)
- Average humidity: 80-85% almost every day
- 70% of days recorded a Discomfort Index (DI) of 80 or higher
🔸 > A DI above 80 means most people feel very uncomfortable.
What Is the Discomfort Index?
Discomfort Index= An indicator of the perceived heat calculated from temperature and humidity
| Discomfort Index | Sensory guideline |
|---|---|
| ≤ 70 | Comfortable |
| 71-75 | Slightly hot |
| 76-80 | Hot and sweaty |
| ≥ 81 | Very hot and uncomfortable |
In 2025, DI values of 81-84 have been reported almost daily in many regions - a level where sleeping or living without air conditioning becomes difficult.
Three Reasons Humidity Stays High
- Rising sea surface temperatures
→ Warmer surrounding seas load the air with moisture - Urban heat island effect
→ Concrete and asphalt trap heat, making night-time cooling difficult - Pressure pattern shifts (Pacific high bias)
→ Moist air mass stagnates, reducing ventilation
Countermeasures: Watch Humidity, Not Only Temperature
Information on heat stroke prevention is attracting attention.
🔷 > WBGT (Wet Bulb Globe Temperature)
This is an index that represents "actual heat stress" including "temperature + humidity + solar radiation (radiant heat)".
- Under 25: Caution
- 25-28: Warning
- 28-31: High alert
- 31 or higher: Dangerous (avoid outdoor activity)
Even if the thermometer reads only 30°C, a WBGT over 31 already signals dangerous conditions.
Conclusion: Summer Risks Go Beyond Temperature
If this summer feels "abnormal," your instincts are right.
There is a humidity trap waiting for those who only watch the temperature.
💡 Trust your senses and make checking humidity, temperature, and sunlight a habit.
In the high-risk summer of 2025, stay safe by monitoring all three.