Question 1 from UPSC CSE 2025 - Geography

Question

Consider the following statements:
I. Without the atmosphere, temperature would be well below freezing point everywhere on the Earth's surface.
II. Heat absorbed and trapped by the atmosphere maintains our planet's average temperature.
III. Atmosphere's gases, like carbon dioxide, are particularly good at absorbing and trapping radiation.
Which of the statements given above are correct?

IASCODEX · Accepted Answer

Correct Option: C. I, II, and III

Strategy: All three statements refer to functions of the atmosphere related to temperature regulation and greenhouse effects. Statement I notes the absence of atmosphere causing below-freezing temperatures—matching Earth's comparison with the Moon. Statement II links the atmosphere's heat-trapping to Earth's average temperature, which reflects the greenhouse effect. Statement III names carbon dioxide as an efficient absorber of radiation—a core greenhouse gas property. No extreme or contradicted assertion exists; all statements are directly supported by well-known Earth science facts.

Key Info: The atmosphere is the layer of gases enveloping the Earth, mainly composed of nitrogen (~78%), oxygen (~21%), argon, and trace gases including carbon dioxide and water vapor. Its functions are pivotal: it provides life-sustaining air, shields from harmful solar UV radiation, and moderates Earth's temperature through the greenhouse effect.

Without the atmosphere, Earth's average surface temperature would be about –18°C (0°F), akin to the Moon, where there is no appreciable atmosphere and extreme temperature swings occur between day and night. The existing atmosphere, through the greenhouse effect, traps outgoing infrared radiation and maintains a habitable global average temperature near +15°C.

The greenhouse effect is driven by specific gases, primarily water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). Carbon dioxide and methane are especially potent at absorbing and reradiating thermal infrared energy from Earth's surface, thereby preventing excessive heat loss to space. Variations in the concentration of these gases directly impact global and regional climate patterns. These processes are fundamental in climatology and earth sciences, affecting weather, habitability, and long-term planetary stability.

IASCODEX · Answer

Option A: I and III only

IASCODEX · Answer

Option B: I and II only

IASCODEX · Answer

Option D: II and III only