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

-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.