Planetary effective radiating temperature ($T_{\mathrm{eff}}=(\mathrm{OLR}/\sigma {)}^{1/4}$)

Define a planet's effective radiating temperature by its actual outgoing longwave flux, regardless of the surface temperature. In radiative equilibrium with solar irradiance $S_0$ and Bond albedo A, $\sigma T_{\mathrm{eff}}^4=(1-A)S_0/4$. A greenhouse effect changes the surface temperature needed to emit that flux. An effective emissivity relating OLR to surface temperature is a diagnostic of the atmosphere–surface system, not necessarily a material emissivity. Away from equilibrium, the outgoing-flux definition and the temperature inferred from absorbed sunlight need not agree.