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UPSC Prelims 2025 GS Paper 1, question 29

Topic: World and physical geography

Q29

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?

  1. (a) I and III only
  2. (b) I and II only
  3. (c) I, II and IIICorrect answer
  4. (d) II and III only

Solution.

Answer: (c) I, II and III

  1. Statement I is correct: without the natural greenhouse effect of the atmosphere, the Earth's equilibrium average surface temperature would be around −18∘-18^\circC, well below the freezing point of water.
  2. Statement II is correct: terrestrial longwave thermal radiation absorbed and re-radiated by the atmosphere maintains the planet's habitable average temperature (around 15∘15^\circC).
  3. Statement III is correct: greenhouse gases such as carbon dioxide, water vapour, and methane selectively absorb outgoing longwave infrared radiation.