Atmospheric depth and temperature (Score 4, Informative)

Even textbooks on this topic don't usually spell out the very simple dependence between atmospheric depth and surface temperature: when you warm the Earth, air molecules 'bounce' higher, so the atmosphere gets deeper. When you cool it, they bounce less high. The higher they fly, the slower they move, unintuitively termed 'adiabatic cooling'.

A small percentage of the highest bouncers can be reheated by the Sun near the top of their bounces, and I assume the reported lower ionosphere is more due to a decline in this factor than to any global cooling.