UPSC Prelims 2025Question 64Geography

The World Bank warned that India could become one of the first places where wet-bulb temperatures routinely exceed 35 °C. Which of the following statements best reflect(s) the implication of the above-said report?
I. Peninsular India will most likely suffer from flooding, tropical cyclones and droughts.
II. The survival of animals including humans will be affected as shedding of their body heat
through perspiration becomes difficult.
Select the correct answer using the code
given below.

Options

(a)I only
(b)II only
(c)Both I and II
(d)Neither I nor II

Correct answer: b

Decision rule

Test each statement against the specific mechanism the report names, not against climate change generally; a true but unrelated consequence does not reflect the implication.

Explanation

Correct Answer:

(b) II only

Explanation of the Correct Answer

The statement from the World Bank about wet-bulb temperatures exceeding 35 °C refers specifically to human survivability limits under extreme heat and humidity conditions.

What is Wet-Bulb Temperature?

It is a combined measure of heat and humidity.
At a wet-bulb temperature of 35 °C, the human body loses the ability to cool itself via sweating, even in the shade, with unlimited water.
Sustained exposure to this temperature can cause organ failure or death in even healthy individuals.

Thus, Statement II is correct:

“The survival of animals including humans will be affected as shedding of their body heat through perspiration becomes difficult.”

Why Other Options Are Incorrect

Statement I:

“Peninsular India will most likely suffer from flooding, tropical cyclones and droughts.”

Incorrect in this context.
While climate change may lead to increased frequency of such events, the specific reference to wet-bulb temperature exceeding 35 °C is about extreme heat and humidity affecting human survivability, not natural disasters.
The World Bank report mentioned focuses on heat stress, not hydro-meteorological events.

Option-wise Analysis

(a) I only – Incorrect: Misinterprets the meaning of wet-bulb temperature.
(b) II only – Correct: Accurately reflects the survival-related implication of high wet-bulb temperatures.
(c) Both I and II – Incorrect: I is unrelated to the stated implication.
(d) Neither I nor II – Incorrect: Statement II is valid.

Relevant Supplementary Information

Wet-Bulb Temperature: Concept Table

Parameter	Dry-Bulb Temp	Humidity	Wet-Bulb Temp	Effect
Moderate Heat, Low Humidity	40 °C	20%	~26–28 °C	Body cools via sweat evaporation
High Heat, High Humidity	40 °C	90%	~34–35 °C	Dangerous zone: body can’t cool effectively
Extreme Wet-Bulb Temp	≥35 °C	Near 100%	≥35 °C	Fatal heat stress in 6 hours or less

Table: Understanding Wet-Bulb Temperature and Its Impacts

Concept	Description
Wet-Bulb Temperature	Temperature a parcel of air would have if cooled to saturation (100% humidity) by evaporation.
Critical Threshold	35 °C – above this, human body loses the ability to cool itself through sweating.
Implication for Humans	Even in shade and with unlimited water, humans cannot survive more than a few hours.
World Bank Warning (2022)	Identified India, Pakistan, and parts of the Persian Gulf as regions vulnerable to surpassing this limit due to climate change.
Affected Sectors	Agriculture, construction, outdoor labor, public health systems, energy demands (for cooling).
Adaptation Measures	Urban greening, heat action plans, shaded shelters, air conditioning access, better housing insulation.

Related Concepts

Heat Index: Combines air temperature and humidity to express what it "feels like".
Climate Hotspots: Regions prone to high wet-bulb temperatures; India is one of them.
Human Heat Tolerance Threshold: Wet-bulb temperature of 35 °C is considered the physiological survivability limit.
Urban Heat Island Effect: Intensifies wet-bulb temperature impacts in cities due to concrete, poor airflow, and pollution.

Current Relevance

India's eastern coastal belt, parts of Telangana, and Uttar Pradesh have recorded wet-bulb temperatures over 31–33 °C in recent years.
Extreme heatwaves in India (2022–2024) have led to health crises, water shortages, and productivity loss.
This issue is critical in the context of climate adaptation policies, urban planning, and public health preparedness.

Table: Concepts and Related Ideas – Wet-Bulb Temperature and Climate Risk

Concept / Term	Description	Relevance to Question	Associated Risks / Impacts
Wet-Bulb Temperature	The lowest temperature air can reach through evaporation at 100% humidity. Measured using a thermometer wrapped in a wet cloth.	Main focus of the World Bank warning. Surpassing 35 °C means human survival is not possible.	Extreme heat stress, inability to cool the body via sweating
35 °C Wet-Bulb Threshold	Upper survivability limit for healthy individuals. Beyond this, human physiology fails.	Core implication: humans and animals cannot survive prolonged exposure.	Heatstroke, organ failure, death within hours
Heat Index	Apparent temperature perceived due to combined effects of heat and humidity. Less precise than wet-bulb temperature.	Related but less severe metric for weather warnings.	Discomfort, reduced productivity, health advisories
Thermoregulation	Body's mechanism to maintain internal temperature through sweating and blood circulation.	Impaired at high wet-bulb temps, leading to collapse of body functions.	Perspiration fails; leads to fatal outcomes
Climate Change	Long-term rise in average temperatures and extreme weather due to greenhouse gases.	Increases frequency and intensity of heatwaves and wet-bulb events.	More regions becoming uninhabitable during summers
Heat Action Plan	Municipal/government policy framework to mitigate effects of extreme heat. Includes cooling shelters, early warnings, and awareness.	India's urban response to heatwaves triggered by rising wet-bulb events.	Reduces mortality, especially among poor and elderly
Urban Heat Island (UHI)	Cities experience higher temperatures due to concrete, lack of vegetation, and heat-trapping materials.	Intensifies wet-bulb conditions in densely populated urban areas.	Localized heat stress, increased energy use for cooling
Climate Vulnerable Zones (India)	Coastal areas (Chennai, Mumbai), Indo-Gangetic Plain (Delhi, Lucknow, Patna), Central India.	Likely to hit wet-bulb thresholds in coming decades.	Risk to public health, migration, productivity loss
World Bank & Climate Reports	Reports warning of wet-bulb extremes in India, especially due to global warming.	Cited in the question; source of the 35 °C projection.	Basis for policy shifts and international aid calls

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