Question

Assertion : Presently, the global atmosphere is warming up.

Reason : The depletion of stratospheric ozone layer has resulted in increase in ultraviolet radiations reaching the earth.

(a) Both A and R are true and R is the correct explanation of A  

(b) Both A and R are true but R is not correct explanation of A  

(c) A is true but R is false  

(d) A and R are false

Answer 1

Correct option (b) 

Explanation :

The warming up of global atmosphere in the present day is due to the increase in green house effect.

Green house effect (GHE) describe the roles of water vapour, CO₂ and other trace gases in keeping the Earth's surface warmer than it would be otherwise. These radiatively active gases are relatively transparent to incoming shortwave radiation (visible spectrum), but are relatively opaque to outgoing reradiating (infrared rays) long-wave radiation. The latter radiation, which would otherwise escape to space, is trapped by these gases within the lower levels of the atmosphere. The subsequent reradiation of some of the energy back to the surface maintains surface temperature higher than they would be if the gases were absent (without the green house effect the Earth's average global temperature would be -18 degree celsius rather than the present 15 degree celsius). There is concern that increasing concentration of the green house gases including CO₂, CH₄, and man made chlorofluorocarbons (CFCs), may enhance the green house effect and cause global warming.

Ozone layer present in the stratosphere is depleted by the aerosols and chlorofluorocarbons. Ozone protects the earth from high energy ultra violet radiation.