Question

Global warming is due to the increase of:
(A) methane and nitrous oxide in atmosphere
(B) methane and ${ CO }_{ 2 }$ in atmosphere
(C) methane and ${ O }_{ 3 }$ in atmosphere
(D) methane and $CO$ in atmosphere

Answer 1

Hint: The unusually rapid increase in Earth’s average surface temperature over the past century is termed as global warming. The major contributors towards global warming are the greenhouse gases that are released due to the burning of fossil fuels.

Complete step by step solution:
Let us first understand the meaning of global warming. The unusually rapid increase in Earth’s average surface temperature over the past century is termed as global warming. The major contributors towards global warming are the greenhouse gases that are released due to the burning of fossil fuels. Between 1906 and 2005, it was observed that the global average surface temperature rose from 0.6 to 0.9 degrees Celsius. The rate of temperature increase has nearly doubled in the last 50 years and it is expected to increase further.
Let us now look into the greenhouse effect. When the sunlight enters the earth’s atmosphere, around 30% of the incoming sunlight is reflected back into space by bright surfaces such as clouds and ice. Most of the remaining 70% sunlight is absorbed by the land and ocean while the rest is absorbed by the atmosphere. This absorbed solar energy is responsible for heating our planet. As the rocks, the air, and the seas warm, they produce thermal infrared radiation. When this energy travels into the atmosphere from the surface, it is absorbed by water vapours and greenhouse gases such as carbon dioxide and methane and radiate heat in all directions. Hence the energy (that was initially coming from the sunlight) is radiated back toward Earth; heating both the lower atmosphere and the surface. This enhances the heating of the earth’s surface as well as the lower atmosphere (that are already getting heated from direct sunlight).

Hence, the correct answer is (B) methane and ${ CO }_{ 2 }$ in atmosphere.

Note: The natural greenhouse effect is beneficial for life on Earth since it keeps the earth’s average surface temperature at around ${ 15 }^{ o }C$. But over the past 250 years, humans activities especially the burning of fossil fuels and deforestation have artificially raised the concentration of greenhouse gases in the atmosphere due to which more of the infrared energy emitted by the surface gets absorbed by the atmosphere due to which the earth’s temperature rises more than what it should causing global warming.