Without greenhouse what would be the average temperature at surface of Earth ?

-18^oC

The correct answer is Option (4) – -18^oC

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 surface of Earth would have been a chilly –18^oC rather than the present average of 15^oC. 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 a times. The gases – carbon dioxide and methane – are commonly known as greenhouse gases because they are responsible for the greenhouse effect.