The natural greenhouse effect is crucial in maintaining the proper temperature for life on earth. Thus,

Greenhouses effect occurring naturally makes temperature control of the atmosphere. If it is absent, there is no warming hence, no vaporization of H2Ol .  Temperature will be lowered, thus only ice appears. If  content increases, more IR radiations are absorbed and warming  takes place.H2Og⇌H2Ol⇌H2OS.