The lapse rate is the rate of cooling with altitude based on the compression of the atmosphere by gravity. Here is a short derivation of the adiabatic lapse rate
Of course, it's not as simple as that, but to first order it predicts a constant decrease in temperature with altitude. The graph to the right is a represents that with a few twists and turns.
One of the bleats of denial, based on such graphs is that "the temperature profile of the atmosphere has nothing to do with the greenhouse effect", but this is not true.
Eli already gave the answer elsewhere, so they who should not be named should be still for a short while.
Eli promises to link to the answer given by Pieter Vermeesch who wrote the New Years Puzzler. Several have already spotted it. You may, of course, choose to differ