Consider the following statements : 1. High clouds primarily reflect solar radiation and cool the surface of the Earth. 2. Low clouds have a high absorption of infrared radiation emanating from the Earth's surface and thus cause warming effect. Which of the statements given above is/are correct ?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2 ✓ UPSC's answer
Why the answer is (d)
• Clouds affect the energy balance in two opposite ways: reflecting sunlight (cooling) and trapping outgoing infrared (warming); which dominates depends on the cloud's height and thickness.
• Statement 1 is wrong: high, thin cirrus clouds let most sunlight through but absorb and re-emit terrestrial infrared, so their net effect is warming.
• Statement 2 is wrong: low, thick stratus clouds strongly reflect solar radiation and, being warm, radiate almost as much heat as the surface, so their net effect is cooling.
• The statements have the roles of high and low clouds reversed.
• Hence neither 1 nor 2, option (d).
Why the other options are wrong
- (a) 1 only
- Statement 1 is wrong: high clouds have a net warming effect.
- (b) 2 only
- Statement 2 is wrong: low clouds have a net cooling effect.
- (c) Both 1 and 2
- Both statements reverse the actual effects.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2022, held on 5 June 2022. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.