Climate & atmosphere

Answer: (a) does not set below the horizon at the Arctic Circle

21 June is the June (northern summer) solstice: the North Pole is tilted towards the Sun, the noon Sun is overhead at the Tropic of Cancer, and every place on or north of the Arctic Circle (about 66½° N) has the Sun above the horizon for the full 24 hours.

• ✓ (a) The Arctic Circle is defined as the southern limit of the zone where the Sun does not set on at least one day a year — the June solstice.
• ✗ (b) On the same day the Antarctic Circle has the opposite: the Sun does not rise, giving 24 hours of night.
• ✗ (c) The noon Sun is overhead at the Equator only at the equinoxes (around 21 March and 23 September).
• ✗ (d) The Sun is overhead at the Tropic of Capricorn at the December solstice (around 22 December); on 21 June it is over the Tropic of Cancer.

Remember · 21 June: Sun overhead at Tropic of Cancer; midnight sun at and north of the Arctic Circle; polar night at the Antarctic Circle. Reversed around 22 December.

📘 Read it in NCERT: Class 7 Curiosity, Ch 12 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (d) Reducing the global warming

Both are proposed geoengineering methods of 'solar radiation modification', meant to cool the planet. Stratospheric sulphate aerosols would reflect sunlight back to space, copying the cooling seen after big volcanic eruptions; thinning heat-trapping cirrus clouds would let more of the Earth's heat escape.

• ✓ (d) The IPCC lists stratospheric aerosol injection and cirrus cloud thinning among the most-studied SRM methods, whose aim is to reduce warming.
• ✗ (a) Artificial rain uses cloud seeding with silver iodide or salt in rain-bearing clouds, not stratospheric sulphate.
• ✗ (b) These methods target the planet's overall heat budget; they are not cyclone-suppression tools.

Remember · Solar radiation modification (geoengineering to cut warming): stratospheric aerosol injection, marine cloud brightening, cirrus cloud thinning, surface albedo change. Carbon dioxide removal is the other branch.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 11 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) Clouds reflect back the Earth's radiation.

Dew forms only when the ground and grass cool below the dew point, and that needs a clear night in which the Earth's heat escapes freely to space. On a cloudy night the clouds send the Earth's heat back down, so the surface stays warmer and no dew forms.

• ✓ (b) Clouds hold back the Earth's outgoing radiation and return part of it towards the surface, keeping the ground from cooling enough for water vapour to condense on it. UPSC treats this as the cause.
• ✗ (a) This is the tempting option. Clouds do take in some of the Earth's radiation, but the answer UPSC accepts is that they send it back, which is what keeps the surface warm.
• ✗ (c) It is the reverse of the truth: with cloud cover the surface stays warmer, and it is a clear, calm, cold night that gives low surface temperature and dew.
• ✗ (d) Dew needs calm air, but clouds do not act by blowing wind down to the ground; the deciding factor is heat loss.

Remember · Dew needs a clear, calm, cold night; cloud cover returns the Earth's heat and stops the surface cooling to the dew point.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 10 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error