Answer:

Correct Answer: C

Solution:

• The mean global temperature rise by $ 2{}^\circ -6{}^\circ C $ and the concentration of carbon dioxide increases in the troposphere up to 600 ppm. Hence, the surface of the earth becomes warm which causes global warming. The phenomenon is similar to that of green house in which the glass enclosed atmosphere gets heated up due to its insulation from the rest of the environment. Hence, global warming is also known as greenhouse effect and the gases responsible for it are called greenhouse gases e. g $ CH _4 $ , $ CO _2 $ etc.