Sweat is the body’s only real defence against overheating. Above a wet-bulb temperature of 35°C, that defence stops working — and the World Bank warns India could be among the first places to face it routinely.
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Wet-Bulb Temperature: The 35°C Line
Heat + humidity, combined into one survivability limit
At 35°C WBTSweat can no longer cool the body
World Bank WarningIndia among first to face it routinely
Most ExposedIndo-Gangetic Plain, coastal humid belts
Not the Same AsFlooding, cyclones, drought
Q64 answer: the implication is physiological (Statement II only) — humans/animals lose the ability to shed body heat through perspiration. It’s not about flooding, cyclones, or drought.
🏛️ Must Know
What Wet-Bulb Temperature Actually Measures
- Not Just Heat Wet-bulb temperature combines heat and humidity into a single number — it’s the lowest temperature achievable by evaporative cooling, like sweat evaporating off skin.
- The 35°C Threshold A wet-bulb temperature of 35°C is theorised as the outer limit of human survivability: at or above it, the body can no longer cool itself through perspiration, even in shade, even at rest.
- Why It’s About Perspiration The direct implication is physiological: the survival of humans and animals is threatened because shedding body heat through sweat becomes difficult or impossible — not because of flooding, cyclones, or drought.
- India at Risk The World Bank has warned India could become one of the first places on Earth to routinely see wet-bulb temperatures cross 35°C, given its combination of high heat and high humidity.
🏘️ Good to Know
Where It Bites Hardest
- Humidity Matters More A wet-bulb temperature of 35°C can occur at a lower actual (dry-bulb) air temperature if humidity is high enough — making humid regions more dangerous than drier, hotter ones.
- Indo-Gangetic Plain India’s northern and coastal plains, especially the Indo-Gangetic belt, combine high summer heat with high humidity, putting them among the most exposed regions globally.
- Recent Research Revises the Number Newer studies suggest the true survivability limit may actually be lower than 35°C for many people, especially older adults, meaning the risk threshold could already be closer than once thought.
- Outdoor Labour at Risk Outdoor workers — construction labourers, farmers, street vendors — face the most immediate risk, since they can’t avoid heat exposure during peak hours.
Test Yourself
📝 Previous Year Question
UPSC CSP 2025 — The Implication of Rising Wet-Bulb Temperatures
- UPSC 2025 The World Bank’s warning about India crossing 35°C wet-bulb temperature is about human/animal survival, since perspiration-based cooling fails — not about flooding, cyclones, or droughts, which are separate climate hazards. See UPSC CSP 2025 GS Paper I, Q64.
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