We are told by greenhouse theorists that backradiation from the sky warms the ground -- 33C warmer than it would otherwise be without the greenhouse effect. In greenhouse theory, backradiation from the sky is recycled and counted again. For example:
NASA "radiation budget", or as I call it: "how to count energy twice"
Some insist that it's not the backradiation that does the warming, it's that light (EMR) is "slowed down" or "trapped" by the greenhouse layer. But even if EMR is trapped optically by the greenhouse gas layer it continues on its merry way in an energy sense.
Even if EMR is trapped by absorption, every photon that is absorbed by the greenhouse gas layer is matched by one that is emitted. This must be so per Kirchhoff's Law, unless the gas layer is changing in temperature. It will change in temperature from time to time, but not overall, not in a way that energy can be gained.