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UPSC Prelims 2022 · World Geography · Air, Winds and Climates
Consider the following statements:
- High clouds primarily reflect solar radiation and cool the surface of the Earth.
- Low clouds have a high absorption of infrared radiation emanating from the Earth’s surface and thus cause a warming effect.
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Show the answer and explanation
Answer: (d) Neither 1 nor 2
Both statements have the roles reversed.
Statement by statement
1. ✗ WRONG — high clouds warm High, thin clouds (cirrus) let most sunlight through but trap outgoing heat. Their net effect is warming.
2. ✗ WRONG — low clouds cool Low, thick clouds (stratus, stratocumulus) reflect sunlight back to space. Their net effect is cooling.
The idea
A cloud affects two energy flows: incoming sunlight and outgoing infrared heat. Its net effect depends on which change is larger. Thin, cold high clouds usually reduce heat loss strongly, while thick low clouds usually reflect enough sunlight to give net cooling. Neither cloud type performs only one of these jobs.
Why the others are wrong
(a) High clouds warm, they don’t cool.
(b) Low clouds cool, they don’t warm.
(c) The two statements swap the roles of high and low clouds.
The trap
Both statements sound physically sensible. UPSC simply swapped “high” and “low” — which is why cirrus-thinning is proposed to cool the planet.
Also know
Cirrus is mainly made of ice crystals; stratus is a layered cloud and cumulus has a puffy form. Cumulonimbus extends through a large vertical depth and can produce thunderstorms. At night there is no sunlight to reflect, so clouds commonly reduce surface cooling. Cloud thickness, height and time of day all matter to the energy balance.
🔒 High clouds (cirrus) → net warming. Low clouds (stratus) → net cooling.
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