The wavelength that comes from the sun is 'complete.' It is basically untouched. It does not cause the heating of Earth. There is a spectific spectrum of wavelength from the sun that causes warming/heating. That specific wavelength is called infrared. It is reflected off the surfaces of Earth. Why? Why is infrared produced by Earth. Well, if Earth receives a full wavelength spectrum from the sun and then utilizes it, will the resultant 'waste wavelength' be the same as the 'utilized wavelength?' No. The utilized wavelength is removed and the 'changed' wavelength is left to reflect back 'toward' space.
