Previous Year 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?
I and III only
I and II only
I, II and III
II and III only
Correct Answer: C
Detailed Solution
Statement I is correct. In the absence of the natural greenhouse effect, the Earth’s average surface temperature would be approximately -18°C, which is well below the freezing point of water. The natural greenhouse effect keeps the Earth’s present average surface temperature at approximately 15°C.
Statement II is correct. After absorbing solar energy, the Earth’s surface emits it as infrared radiation. Greenhouse gases in the atmosphere absorb a part of this heat and re-radiate it in different directions. This slows the loss of heat to space and maintains the Earth’s average temperature at a level suitable for life.
Statement III is correct. Greenhouse gases such as carbon dioxide, water vapour, methane and nitrous oxide effectively absorb the infrared radiation emitted by the Earth’s surface.
The atmosphere allows most of the incoming short-wave solar radiation to reach the Earth’s surface but absorbs a part of the outgoing long-wave infrared radiation. This is known as the natural greenhouse effect.
The natural greenhouse effect is essential for life. The trapping of heat by the atmosphere mentioned in the question refers to the natural greenhouse effect and not merely to human-induced global warming.