So, the «back radiation» from the greenhouse gas can only heat the surface (at best) to less than the surface radiating temperature which «warmed» the greenhouse gas. (realclimate.org)
On average, there won't be a change in the equilibrium radiating temperature of the Earth, but there will be a change in the effective radiating altitude consequent on the change in the atmosphere's effective thermal conductance. (rabett.blogspot.ru)
The upwelling version has a wide field of view for measuring the narrowband radiating temperature of the ground surface. (arm.gov)