Question

Which of the following pairs of gases is mainly responsible for the greenhouse effect?
A. Ozone and Ammonia
B. Oxygen and Nitrogen
C. Nitrogen and Sulphur Dioxide
D. Carbon dioxide and Methane

Answer 1

The greenhouse effect is a natural process that warms the Earth's surface. When the Sun's energy reaches the Earth's atmosphere, some of it is reflected back to space and the rest is absorbed and re-radiated by the greenhouse gases. The absorbed energy during this process warms the atmosphere and the surface of the Earth.

Complete answer: The greenhouse effect is the increase in $C{O_2}$ concentration in the atmosphere that makes the thick layer transparent to incoming solar radiations but opaque to outgoing terrestrial radiations. This thick layer of $C{O_2}$ functions like the glass panels of the greenhouse or glasshouse (that is like the glass window of a car). It allows the incoming solar radiation to filter through and prevent the heat from radiating out into the outer space. If we go 100 years back, the $C{O_2}$ was $275ppm$, but today it has reached upto $350ppm$ and by 2035, it has been estimated that it would reach to about $450ppm$. The main gases responsible for greenhouse effect are $C{O_2}$ $(60\% )$, $CFCs$ $(14\% )$, ${N_2}O$ $(6\% )$, $C{H_4}$ $(20\% )$. Among them, $C{O_2}$ and $C{H_4}$ contribute the most towards greenhouse effects and hence, they are called greenhouse gases. Its main effect can be seen in increasing global temperature (called global warming). In the past century, global temperature has increased by ${0.6^\circ }C$. It has been seen that, $C{O_2}$ increases the earth’s temperature by $50\%$, while $CFCs$ are responsible for another $20\%$ rise. The excess $C{O_2}$ to some extent is absorbed by oceans, but due to industrialisation, the energy consumption releases $C{O_2}$ at a faster rate than the capacity of the ocean to absorb it. A rise of five degrees in the atmospheric temperature would raise the sea level by five meters within a few decades, threatening all the coastal cities.
Hence, the correct answer is option D.

Note: According to scientists, the coming generations would suffer from more hurricanes, typhoons and cyclones. One of the major causes of the greenhouse effect is deforestation. About $40\%$of forests are cleared from tropics and $1\%$ from the temperate region. In India, at the start of the twentieth century, forests covered about 30 percent but at the end of the twentieth century, it reduced to about 19.4 per cent.