📘 IAS Prelims 2025 — GS-I Q.29 | Classroom Explanation

📌 Question

Q.29) Consider the following statements:

I. Without the atmosphere, temperature would be well below freezing point everywhere on the Earth’s surface.
II. Heat absorbed and trapped by the atmosphere maintains our planet’s average temperature.
III. Atmosphere’s gases, like carbon dioxide, are particularly good at absorbing and trapping radiation.

Which of the statements given above are correct?

(a) I and III only
(b) I and II only
(c) I, II and III
(d) II and III only

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✅ Correct Answer: (c)

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🧑‍🏫 Classroom Explanation

This question tests understanding of the natural greenhouse effect and the role of Earth’s atmosphere in temperature regulation, a foundational concept in climatology and environmental geography.

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🔍 Key Concept: Atmosphere and Earth’s Heat Balance

• The atmosphere is a mixture of gases surrounding the Earth
• It performs multiple life-supporting functions:

• Supplies breathable air
• Shields Earth from harmful ultraviolet radiation
• Moderates temperature extremes
• Traps heat through the natural greenhouse effect

Without the atmosphere, Earth would resemble a cold, lifeless planet.

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🔍 Statement-wise Analysis

✅ Statement I: Correct

• In the absence of atmosphere:

• Solar radiation would escape freely back into space
• There would be no greenhouse effect
• Earth’s average surface temperature would fall to about –18°C

• This would place temperatures well below freezing across most of the planet

➡️ Hence, Statement I is correct.

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✅ Statement II: Correct

• The atmosphere absorbs and re-radiates heat back toward Earth
• This process:

• Maintains an average surface temperature of about 15°C
• Prevents extreme day–night temperature variations

➡️ Hence, Statement II is correct.

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✅ Statement III: Correct

• Certain atmospheric gases, called greenhouse gases, are especially effective at:

• Absorbing outgoing infrared radiation
• Trapping heat within the lower atmosphere

• Examples include:

• Carbon dioxide (CO₂)
• Methane (CH₄)
• Water vapour

➡️ Hence, Statement III is correct.

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🧮 Logical Elimination (UPSC Style)

• Statement I → True
• Statement II → True
• Statement III → True

➡️ All statements are correct.

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🎯 Final Answer

✅ Correct Answer: (c) I, II and III

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📦 Info Box — Extra Points (Prelims Value Add)

• Natural greenhouse effect is essential for life
• Enhanced greenhouse effect leads to global warming
• Moon has no atmosphere → extreme temperature variation
• Venus has dense CO₂ atmosphere → runaway greenhouse effect

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🔗 Bridge Points (Future Questions)

• Radiation balance of Earth
• Difference between greenhouse effect and global warming
• Role of water vapour as a feedback mechanism

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📍 GS Mapping

GS Paper I
Subject: Geography
Theme: Climatology — Atmosphere & Temperature
Nature: Conceptual

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