The atmospheric engine

I have been following a discussion on this website which is trying to shed some light on the carbon dioxide climate change theory, which seems to be based on spurious assumptions. The carbon dioxide claim is that the earth is warmer at the surface than it would be in the absence of carbon dioxide in the atmosphere, from which it follows that an increase in concentration of this gas would lead to global warming, which must now be stopped as a matter of urgency. The alternative theory is that the temperature at the surface of the earth is simply determined by the  action of gravity on the atmosphere in response to the heat it receives from the sun.

It is common knowledge that the atmosphere gets thinner, and that the atmospheric pressure and temperature get, lower, the higher you go. Think of the conditions at the top of Mount Everest. The atmosphere is an ocean of compressible gas resting on the solid surface of the earth; as a great over-simplification, it can be considered as an assembly of columns of air about 25 km tall, with a temperature of about 15 degrees C at the base and around minus 15 to minus 30 at the top, where it merges into outer space; the fall-off in temperature with height is known as the ‘lapse rate’. At ground level, the pressure is that due to the mass of a layer of air on top of it, approximately 25 km tall, which is the same as a column of mercury 75 cm tall, which adds up to quite a lot. The air is, as a consequence, relatively compressed – 15 lbs per square inch in old money. At the top of the atmosphere, the pressure can be considered to be zero.

Each column of air receives energy from radiation from the sun at its upper end, which passes through the column and is absorbed by the ground, which then heats up. This sets up what amounts to a heat engine. Heat engines work on the adiabatic principle. If you quickly compress the air in a bicycle pump it becomes warmer. The energy for this warming comes from your work. The same principle is applied in a diesel engine, where the temperature rises to the point where a small amount of fuel will burn if it is forced into the hot cylinder. This happens explosively and the piston is forcibly moved as the gas expands. This force can be transferred to a drive system and the energy can thereby be utilised in an engine. This expansion happens adiabatically ie the temperature falls as the gas expands.

This is more easily seen in a steam engine, where a puff of hot steam under pressure is admitted to the cylinder, and the steam expands and pushes the piston. What happens to the steam? It expands to several times its original volume and its pressure and temperature falls, so that it is on the verge of turning into water, which is what you see coming out of the chimney. This is an adiabatic process ie no energy is absorbed or released through the walls of the cylinder, due to the speed with which the expansion occurs. The energy in the hot steam, which was originally chemical energy in the fuel, has been used to make the wheels go round.

I cannot quite picture this myself but I assume that there is a similar process results in the relatively high temperature at ground level and the existence of a lapse rate; the radiation energy flux arriving at the edge of the atmosphere, passes through the atmosphere to the surface, where it is absorbed and heats the surface. This effectively sets up a heat engine, resulting in the lapse rate described.

On this theory, the carbon dioxide effect on Venus might be attributable not to the IR absorption effect but to the higher density of CO2, which has a molecular weight of 44 compared to the average molecular weight of air which is about 29 ie the molecules of CO2 are 1.5 times heavier. If this is the case, the war on carbon is an expensive and futile diversion.