Why heat and humidity tend to stay in the air

When sun shines on a forest, the trees in it fix solar energy, CO₂ and H₂O into wood cellulose. If the wood is burnt, the solar energy is released as Q while the CO₂ and _G.H₂O are returned to the air in smoke. This also happens when organic materials rot. Dead leaves fall on the ground in autumn. In winter, they rot to nutrients and _L.H₂O that seep down into the soil while CO₂ is released into the air. Q is also returned to the environment. A compost heap can become so warm that steam rises out of it- rotting rags can catch fire. This effect reduces winter cold in forested regions. In spring and summer plants again bind H₂O, CO₂ and Q into their bodies.

If forests are cleared or burnt, and not replanted, Q, CO₂ and _G.H₂O discharged into the air tend to remain there. The phenomenon has been accelerating since the Industrial Revolution. Fossil fuels contain chemically stored solar energy, CO₂ and _L.H₂O. Air gets hotter and drier when fossil fuels are burnt in it. It can thus absorb more Φ from the environment than it received from combustion gasses. Combustion exhaust gasses have a larger P x V (V = volume) enthalpy component than the inlet air did as well as more LQ and SQ. The enthalpy difference is added to the atmosphere. It does not only become hotter, it also becomes bigger and wetter.

At a given P, warmer, wetter air is lighter (smaller ρ) than dry air. If its P is reduced or its T increased, it can absorb more Φ before it saturates. This effect is cumulative. As more fossil fuels are burnt, the earth's atmosphere becomes thicker, warmer and lighter. Some of the Φ added to the air does not rain out again because warmer air can contain more Φ before it becomes saturated. More of the Q added to it by burning fossil fuels remains in the atmosphere as LQ- and this does not rain out (Foehn effect). The atmosphere may trap a little heat (greenhouse effect); it radiates almost no heat into outer space.Other conditions equal, and according to the first, energy constance, Law Of Thermodynamics, most of the new Q added to the atmosphere when fossil or nuclear fuels are burnt remains permanently in the atmosphere.