Consider the following statements:
Statement-1: The atmosphere is heated more by incoming solar radiation than by terrestrial radiation. Statement-II: 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?
(a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
(b) Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I
(c) Statement-I is correct, but Statement-II is incorrect
(d) Statement-I is incorrect, but Statement-II is correct
Explanation
The correct answer is: (d) Statement-I is incorrect, but Statement-II is correct.
- Statement-I is incorrect: The atmosphere is not heated more by incoming solar radiation than by terrestrial radiation. Instead, it is mainly heated by long wave terrestrial radiation. The Earth’s surface absorbs shortwave solar radiation and re-radiates it as longwave infrared radiation, which is then absorbed by greenhouse gases in the atmosphere, heating it from below.
- Statement-II is correct: Carbon dioxide and other greenhouse gases in the atmosphere are indeed good absorbers of long wave radiation. These gases absorb the infrared radiation emitted by the Earth’s surface and re-radiate it, contributing to the warming of the atmosphere.
Learn more
- Terrestrial Radiation:
- The Earth receives solar energy in the form of shortwave radiation.
- After absorbing this energy, the Earth re-radiates it as longwave infrared radiation.
- This longwave radiation is absorbed by atmospheric gases, particularly carbon dioxide and other greenhouse gases.
- This process is known as terrestrial radiation and is the primary way the atmosphere is heated.
- Greenhouse Effect:
- Greenhouse gases such as water vapor, carbon dioxide, methane, and others absorb longwave infrared radiation emitted by the Earth’s surface.
- These gases then re-radiate the energy in all directions, including back towards the Earth’s surface, creating a warming effect known as the greenhouse effect.
- This effect is crucial for maintaining the Earth’s temperature, making it habitable.
- Insolation:
- Insolation refers to the incoming solar radiation that reaches the Earth’s surface.
- The atmosphere is largely transparent to this shortwave solar radiation, allowing it to pass through and be absorbed by the Earth’s surface.
- However, the atmosphere absorbs only a small fraction of this shortwave radiation directly.
- Energy Balance:
- The Earth’s energy balance involves the absorption of solar radiation and the emission of terrestrial radiation.
- Approximately 30% of incoming solar radiation is reflected back to space, while the remaining 70% is absorbed by the Earth’s surface and atmosphere.
- The absorbed energy is eventually re-radiated as longwave infrared radiation, which is then absorbed by greenhouse gases, maintaining the Earth’s energy balance and temperature.
- Role of Greenhouse Gases:
- Water vapor and carbon dioxide are the most significant greenhouse gases in terms of their ability to absorb and re-radiate infrared radiation.
- These gases trap heat within the atmosphere, preventing it from escaping into space, thus warming the planet.
- Without the natural greenhouse effect, the Earth’s average temperature would be significantly lower, making it less hospitable for life.
By understanding these processes, it becomes clear that the atmosphere is primarily heated by terrestrial radiation rather than direct solar radiation, and greenhouse gases play a crucial role in this heating mechanism.
