Assertion A Without Greenhouse gases Earth would be a frozen wasteland Reason R The balance of insol...........

Geography and Environment (PCS) World climates

Assertion (A): Without Greenhouse gases, Earth would be a frozen wasteland.

Reason (R): The balance of insolation and outgoing radiation results in a constancy of average temperature of earth’s surface.

if both A and R are true and R is the correct explanation of A

if both A and R are true but R is not the correct explanation of A

if A is true but R is false

if A is false but R is true

Explanation: Both these statements are correct.

The earth’s surface absorbs insolation and radiates it in the form of thermal energy (infrared radiation) that heads back upward. If the earth had no atmosphere, all this energy would escape back into space. But our planet does have an atmosphere, and certain gases (water vapour, carbon dioxide, methane, nitrogen dioxide and ozone) in air absorb thermal radiation and re-radiate it. In effect, these gases trap infrared radiation and keep the lower atmosphere warm.
Since the amount of incoming solar radiation is nearly equal to the amount of outgoing terrestrial radiation for Earth as a whole, the average worldwide temperature remains constant.