Q. Consider the following statements : - Without the atmosphere, temperature would be well below freezing point everywhere on the Earth's surface.
- Heat absorbed and trapped by the atmosphere maintains our planet's average temperature.
- Atmosphere's gases, like carbon dioxide, are particularly good at absorbing and trapping radiation.
Which of the statements given above are correct? (UPSC Prelims 2025)
Answer:
I, II and III
Notes: The correct answer is
[C] I, II and III. These statements describe the Greenhouse Effect, a natural process that warms the Earth's surface to a level capable of supporting life.
- Statement 1 (Correct): Without an atmosphere, the Earth would have no way to retain the heat it receives from the Sun. Calculations suggest that without the greenhouse effect, the Earth’s average surface temperature would be approximately -18°C, well below the freezing point of water, instead of the current comfortable average of about 15°C.
- Statement 2 (Correct): The atmosphere acts like a thermal blanket. While it allows short-wave solar radiation to pass through and reach the surface, it absorbs and traps the long-wave terrestrial radiation (heat) emitted by the Earth. This energy is then re-radiated back toward the surface, maintaining a stable temperature range.
- Statement 3 (Correct): Certain gases, known as Greenhouse Gases (GHGs), are highly efficient at absorbing infrared radiation. Carbon dioxide (CO2), water vapor, methane, and nitrous oxide are the primary natural components that facilitate this trapping of heat. While nitrogen and oxygen make up 99% of the atmosphere, they do not significantly contribute to this specific warming effect.
The Mechanism:
The Earth's surface, warmed by sunlight, radiates energy back toward space in the form of infrared (thermal) radiation. Greenhouse gases like CO2 absorb this outgoing heat and re-emit it in all directions, effectively "trapping" it within the lower atmosphere. This process is essential for life, though human-induced increases in these gases are currently leading to enhanced global warming.