Without green house effect, the average temperature of earth surface would be

Question

UnlockIAS · Accepted Answer

Correct — B, about –18°C. If Earth had an atmosphere with no greenhouse gases (or no atmosphere at all), the surface would be warmed only by absorbed sunlight and would radiate that energy straight back to space. Balancing incoming solar energy against outgoing long-wave radiation — for Earth's albedo (~0.3) and its distance from the Sun — gives an effective (equilibrium) temperature of roughly 255 K, which is about –18°C. Earth's actual global average surface temperature is about +15°C, so the natural greenhouse effect adds about 33°C of warming, which is what makes the planet habitable. The standard textbook figure for 'no greenhouse effect' is therefore –18°C.

Why the other options are wrong — (a) 0°C is the freezing point of water, not Earth's no-greenhouse equilibrium temperature; the radiative-balance value is colder, about –18°C.  (c) Too warm — 5°C is close to today's climate range, not the frozen equilibrium a greenhouse-free Earth would reach.  (d) Close but not the standard figure; the accepted textbook value for Earth's effective temperature is about –18°C (255 K), not –20°C.

Concept: The greenhouse effect is the warming of a planet's surface because atmospheric gases (water vapour, CO2, methane, nitrous oxide, ozone) are largely transparent to incoming short-wave solar radiation but absorb and re-emit outgoing long-wave (infrared) radiation from the surface. This traps heat in the lower atmosphere. Earth's 'effective temperature' — the temperature it would have from radiative balance alone, without this trapping — is about 255 K (–18°C); the actual surface average is ~15°C.

State PCS 2020 Q83 — Environment & Ecology PYQ with Answer

State PCS 2020 Q83 — Environment & Ecology PYQ with Answer