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UPSC 2001: Cloudy nights are warmer compared to clear cloudless nights, because clouds
(a)prevent cold waves from the sky from descending on Earth
(b)reflect back heat given off by Earth
(c)produce heat and radiate it towards Earth
(d)absorb heat from the atmosphere and send it towards Earth
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Not attemptedCorrect Answer: (b) reflect back heat given off by Earth
Clouds act like an insulating blanket: water-droplet and ice crystals absorb the long-wave (infra-red) radiation emitted by Earth’s surface and re-radiate a portion of it back downward, reducing night-time radiational cooling. Hence cloudy nights remain warmer, so option (b) is correct; the other options wrongly speak of ‘cold waves’, ‘producing heat’ or ‘absorbing heat from the atmosphere’, none of which explains the observed warming. ([psl.noaa.gov](https://psl.noaa.gov/outreach/education/science/clouds_and_climate.html))
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Frequently Asked Questions
What is the correct answer to this UPSC 2001 Geography question?▼
The correct answer is option (b): reflect back heat given off by Earth. Watch the detailed video explanation in our Sherlocking Prelims course on UnlockIAS.
Which year was this Atmosphere & Climatology question asked in UPSC Prelims?▼
This question was asked in UPSC CSE Prelims 2001, GS Paper 1, as Question 111. It falls under Geography > Atmosphere & Climatology.
What is the difficulty level of this UPSC question?▼
This question is rated "easy". It tests basic recall and most well-prepared aspirants should answer it correctly.
How many UPSC Prelims questions have been asked from Atmosphere & Climatology?▼
UPSC has asked 70 questions from Atmosphere & Climatology (under Geography) across multiple years. Visit the topic page to see the full list and year-wise trends.