The increasing amount of carbon dioxide in the air is slowly raising the temperature of the…

Answer: (d) the infrared part of the solar radiation

Carbon dioxide is a greenhouse gas. Incoming sunlight passes through it, but it absorbs the infrared (long-wave) heat that the warmed Earth radiates back. This traps heat in the atmosphere, so more CO2 means a warmer atmosphere.

• ✓ (d) The Earth's surface absorbs sunlight and re-emits that energy as infrared heat. CO2 absorbs this outgoing infrared and re-radiates part of it back towards the surface, slowing heat loss to space and warming the lower atmosphere. The infrared is ultimately the Sun's energy in another form, which is why this option is the right one.
• ✗ (a) CO2 does not absorb water vapour. Water vapour is a separate greenhouse gas that absorbs heat on its own.
• ✗ (b) The heating effect of CO2 does not come from absorbing ultraviolet light. The greenhouse effect works on outgoing long-wave (infrared) radiation.
• ✗ (c) CO2 is transparent to incoming solar radiation, so it does not absorb all of it. It is opaque to the outgoing terrestrial (infrared) radiation.

Remember · CO2 is transparent to incoming short-wave sunlight but absorbs outgoing long-wave (infrared) terrestrial radiation. This is the core of the greenhouse effect.

📘 Read it in NCERT: Class 11 Fundamentals of Physical Geography, Ch 7 (practise this chapter) · Class 11 Fundamentals of Physical Geography, Ch 11 (practise this chapter)

Question: UPSC Civil Services (Preliminary) 2012, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). · Report an error