Question 35 from UPSC CSE 2024 - Geograph y

Question

Consider the following statements:
1. The atmosphere is heated more by incoming solar radiation than by terrestrial radiation.
2. Carbon dioxide and other greenhouse gases in the atmosphere are good absorbers of long-wave radiation.
Which one of the following is correct in respect of the above statements?

IASCODEX · Accepted Answer

Correct Option: D. Statement-I is incorrect, but Statement-II is correct

Strategy: - Analyze how the question differentiates atmospheric heating by incoming solar (shortwave) and terrestrial (longwave) radiation.
- Apply atmospheric physics knowledge: the atmosphere primarily absorbs Earth's longwave radiation, not direct solar shortwave energy.
- Determine Statement I as incorrect and Statement II as correct, confirming greenhouse gases absorb longwave radiation.
- Conclude by eliminating other options to arrive at option D.

Key Info: Atmospheric heating primarily results from terrestrial radiation. Solar energy, arriving as shortwave radiation (visible and near-infrared), largely passes through the atmosphere. The Earth's surface absorbs this shortwave radiation and re-emits it as longwave (infrared) radiation.

The atmosphere, particularly greenhouse gases like carbon dioxide, water vapor, methane, and ozone, absorbs this outgoing longwave radiation. This absorption leads to atmospheric warming--a process known as the natural greenhouse effect. The lower atmosphere is heated mainly from below by contact with the Earth's warmed surface and the absorption of terrestrial radiation, not directly by sunlight. Greenhouse gases are crucial for maintaining Earth's temperature through their selective absorption and re-radiation of infrared energy.

A fundamental point in climatology is that incoming solar radiation is not the primary direct heat source for the atmosphere.

**Key Concepts:**
- **Shortwave radiation:** Visible/UV light from the Sun.
- **Longwave radiation:** Infrared radiation emitted from Earth.
- **Atmospheric gases:** Play critical absorptive roles in the greenhouse effect.

IASCODEX · Answer

Option A: Both Statement-I and Statement-II are correct and Statement-II explains Statement-I

IASCODEX · Answer

Option B: Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I

IASCODEX · Answer

Option C: Statement-I is correct, but Statement-II is incorrect