As I understand it, technically speaking, the earth is in energy-balance, meaning that all the incoming solar energy gets absorbed and re-radiated back out into space. The key to the greenhouse effect is that the level in the atmosphere at which the IR photons re-radiate back out into space gets higher and higher and less efficient. This winds up trapping more heat at the surface but ultimately those IR photons will make it back out into space.
Earth is an open system. The theory doesn't work unless it is a closed system.