Question

The greenhouse effect is mainly due to
A. $SO_2$
B. $CO_2$
C. CO
D. $O_2$

Answer 1

Hint: The greenhouse effect is a natural process that keeps the earth’s temperature warm. Greenhouse gases are those gases that emit and absorb radiant energy within the thermal infrared range.

Complete Answer:
- The greenhouse gas effect is a process in which heat is trapped close to the earth’s surface by greenhouse gases.
- When solar energy or solar radiation falls on the earth, 30 % of solar energy is reflected back to space and 70% is passed through the earth’s atmosphere. It is absorbed by land, oceans, and atmosphere and thus heat up the earth.
- Now, earth re-emits heat in the form of infrared radiation. All infrared radiation does not escape from the atmosphere but gets absorbed by the atmospheric gases (e.g., carbon dioxide, methane, etc.) known as greenhouse gases and are redirected back toward the earth, thereby keeping the earth warm.
- The concentration of greenhouse gases has jumped in the past century due to increased human activities such as burning fossils, increased number of vehicles, and deforestation.

Option a: Sulfur dioxide ($SO_2$) is not said to be a direct greenhouse gas as it does not absorb and trap infrared radiation as it attempts to return. Therefore, this is an incorrect option.

Option b: Carbon dioxide is the primary greenhouse gas emitted through human activities. The concentration of carbon dioxide ( $CO_2$) has recently increased as it has entered the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, and trees. It has also increased due to certain chemical reactions such as the manufacture of cement. Therefore, this is the correct option.

Option c: Carbon monoxide or CO is not said to be a direct greenhouse gas as it does not absorb and trap infrared radiation as it attempts to return. Therefore, this is an incorrect option.

Option d: Oxygen or $O_2$ is not a greenhouse gas as they are transparent to infrared light. Therefore, this is an incorrect option.

Note: The naturally occurring greenhouse gases are water vapor, carbon dioxide, ozone, methane, and nitrous oxide.