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 ✓ UPSC's answer
Why the answer is (d)
• Incoming solar radiation is short-wave; the atmosphere is largely transparent to it and absorbs only about a fifth, so most of it reaches and heats the ground.
• The warmed Earth re-radiates energy as long-wave (infrared) radiation, which water vapour, carbon dioxide and other greenhouse gases absorb strongly — Statement-II is correct.
• Consequently the atmosphere is heated mainly from below, by terrestrial radiation (plus conduction and convection), not by incoming solar radiation; Statement-I is therefore incorrect.
• This is why temperature normally falls with altitude in the troposphere and why the greenhouse effect warms the lower atmosphere.
• Hence option (d).
Why the other options are wrong
- (a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
- Statement-I is wrong: the atmosphere is heated mainly by terrestrial radiation.
- (b) Both Statement-I and Statement-II are correct, but Statement-II does not explain…
- Statement-I is wrong, so both cannot be correct.
- (c) Statement-I is correct, but Statement-II is incorrect
- It is Statement-I that is incorrect and Statement-II that is correct.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2024, held on 16 June 2024. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.