Greenhouse Effect - Definition, Causes And its Effects - Practice Questions & MCQ

• The term ‘Greenhouse effect’ has been derived from a phenomenon that occurs in a greenhouse. 
• Greenhouse looks like a small glass house and is used for growing plants especially during winter.
• In a greenhouse the glass panel lets the light in, but does not allow heat to escape.
• Therefore, the greenhouse warms up, very much like inside a car that has been parked in the sun for a few hours.
• The greenhouse effect is a naturally occurring phenomenon that is responsible for heating of Earth’s surface and atmosphere. 
• Without greenhouse effect the average temperature at the surface of Earth would have been a chilly –18oC rather than the present average of 15oC. 

In order to understand the greenhouse effect, it is necessary to know the fate of the energy of sunlight that reaches the outermost atmosphere.

• Clouds and gases reflect about one-fourth of the incoming solar radiation, and absorb some of it but almost half of incoming solar radiation falls on Earth’s surface heating it, while a small proportion is reflected back. 
• Earth’s surface re-emits heat in the form of infrared radiation but part of this does not escape into space as atmospheric gases (e.g., carbon dioxide, methane, etc.) absorb a major fraction of it. 
• The molecules of these gases radiate heat energy, and a major part of which again comes to Earth’s surface, thus heating it up once again.
• This cycle is repeated many times. 
• The above-mentioned gases – carbon dioxide and methane – are commonly known as greenhouse gases because they are responsible for the greenhouse effect.