Authentic Classroom Explanation by IAS Monk

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📍 The Question

Consider the following statements:

Statement-I:
The atmosphere is heated more by incoming solar radiation than by terrestrial radiation.

Statement-II:
Carbon dioxide and other greenhouse gases in the atmosphere are good absorbers of long-wave radiation.

Which one of the following is correct in respect of the above statements?

(a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
(b) Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I
(c) Statement-I is correct, but Statement-II is incorrect
(d) Statement-I is incorrect, but Statement-II is correct

Correct Answer: (d) Statement-I is incorrect, but Statement-II is correct

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🎯 Theme of the Question

Physical Geography | Climatology | Heat Budget | Radiation Balance

This is a concept-heavy climatology question testing understanding of how the atmosphere actually gets heated.

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🧠 Classroom Explanation

Let us analyse both statements step by step.

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🔹 Statement-I: The atmosphere is heated more by incoming solar radiation than by terrestrial radiation. ❌

• The atmosphere is largely transparent to short-wave solar radiation
• Incoming solar radiation:
  • Passes through the atmosphere
  • Directly heats the Earth’s surface, not the air
• Only a small portion of solar radiation is absorbed by:
  • Ozone
  • Water vapour
  • Dust particles

👉 The atmosphere is not primarily heated by incoming solar radiation

✘ Statement-I is incorrect

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🔹 Statement-II: Carbon dioxide and other greenhouse gases are good absorbers of long-wave radiation. ✅

• The Earth, after being heated, emits energy as long-wave (infrared) radiation
• Greenhouse gases such as:
  • Carbon dioxide
  • Methane
  • Water vapour
• Strongly absorb this long-wave radiation
• This absorption heats the atmosphere from below

This process is called terrestrial radiation heating

✔️ Statement-II is correct

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📊 Final Assessment

Statement	Status
Atmosphere heated more by solar radiation	❌ Incorrect
Greenhouse gases absorb long-wave radiation	✅ Correct

👉 Correct answer: (d)

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❌ UPSC Elimination Logic

• UPSC tests the counter-intuitive idea:
  • Air is heated mainly from below, not directly by the Sun
• Short-wave radiation heats the surface
• Long-wave radiation heats the atmosphere

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🧩 Memory Hook

“The Sun heats the ground; the ground heats the air.”

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🧠 Prelims Strategy Insight

For climatology questions:

• Remember:
  • Short-wave → surface
  • Long-wave → atmosphere
• Greenhouse effect operates on terrestrial radiation, not incoming solar rays

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🧭 IAS Monk Whisper

The sky warms not by facing the Sun, but by listening to the Earth beneath it.