UPSC Prelims 2025 · GS Paper I
Question 29: Geography
Consider the following statements :
- IWithout the atmosphere, temperature would be well below freezing point everywhere on the Earth’s surface.
- IIHeat absorbed and trapped by the atmosphere maintains our planet’s average temperature.
- IIIAtmosphere’s gases, like carbon dioxide, are particularly good at absorbing and trapping radiation.
Which of the statements given above are correct?
AnswerThe answer is (c).
Gases such as carbon dioxide, water vapour and methane absorb the long-wave heat radiated by the Earth and send some of it back, so the atmosphere traps heat and keeps the planet's average temperature near 15 degrees Celsius. Without this natural greenhouse effect, the average would be about minus 18 degrees Celsius, well below freezing. The word 'everywhere' in Statement I is a textbook simplification of that average. All three statements are accepted as correct.
- I. Without an atmosphere the average surface temperature would be far below freezing.
- II. Heat absorbed and trapped by the atmosphere maintains the planet's average temperature.
- III. Carbon dioxide and similar gases absorb and trap radiation.
How you could have got this
- If you were sure statement I is correct, (d) goes: it leaves I out.
What you needed to know: Without an atmosphere the average surface temperature would be far below freezing.
- Then, if you were sure statement II is correct, (a) goes: it leaves II out.
What you needed to know: Heat absorbed and trapped by the atmosphere maintains the planet's average temperature.
- Then, if you were sure statement III is correct, (b) goes: it leaves III out.
What you needed to know: Carbon dioxide and similar gases absorb and trap radiation.
Only (c) is left. This one needs every statement.
This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: Statement II about trapped heat is also correct.
- (b) Wrong: Statement III on carbon dioxide absorbing radiation is also correct.
- (c) Right: all three statements describe the greenhouse effect.
- (d) Wrong: Statement I is also accepted as correct.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2025, General Studies Paper I, Series A. The paper on upsc.gov.in.