Greenhouse Gas Effect causes Surface Cooling
A E Banner
Greenhouse gases such as carbon dioxide, methane and water vapour in the atmosphere absorb some of the power radiated to space from the Earth’s surface. More carbon dioxide causes more absorption, and so the power radiated to space becomes less than the input power from the Sun, and the required condition of power balance is thereby disturbed.
The GHG theory for global warming claims that this causes the surface temperature to rise in accordance with the Stefan-Boltzmann Law so that the output power flow to space is restored to its original value. Energy balance is thus established again.
However, the theory has been hampered for more than 30 years by attempts by climate scientists to reconcile climate events with increases in the atmospheric concentration of carbon dioxide. It was implicitly accepted that such climate events depended ultimately on the temperature of the land surface, and that this temperature could be affected by greenhouse absorptions of energy.
The early attempts to establish the theory completely ignored the water vapour in the atmosphere; but this is by far the most important absorbing molecule present. Consequently much work proceeded to try to overcome the difficulties, such as introducing the idea of “climate forcings”. So the theory became more and more complicated. Thoughts of energy were considered, but the theory completely ignored the most fundamental principle of Physics, namely the Law of Conservation of Energy.
Basic facts for a new approach
This is based simply upon energy considerations.
The power absorbed from the Sun is taken throughout to be constant.
There are two fundamental requirements
(a) The Law of Conservation of Energy must be obeyed.
(b) The output power must be equal to the input power. This is the energy (power) balance condition.
It is universally accepted that the power radiated from the surface increases with increases in the temperature, in accordance with the Stefan-Boltzmann Law.
Carbon dioxide and other greenhouse gases in the atmosphere absorb some of the radiant energy (power) emitted from the surface. This energy is then re-radiated and is absorbed into the surface. The difference between the surface power and the output power to space is called the “greenhouse effect”.
The diagram shows the situation, where the surface temperature T is the Absolute temperature in degrees Kelvin.
From Sun Surface Space
Pin Psurf Pout
ǀ ˂ ˂ ˂ ǀ
Pin is the input power from the Sun, taken to be constant.
Pout is the output power to space.
Psurf is the power radiated from the surface.
Pgh is the greenhouse effect
Let Ptot be the total power in the Earth’s system
So, Ptot = Pin + Pout + Psurf + Pgh
Therefore, Psurf = Ptot – (Pin + Pout + Pgh) ………………………(1)
In the stable equilibrium condition of energy balance before anthropogenic activities, the surface temperature attained a value which depended on the power from the Sun and on the concentration of greenhouse gases at that time.
Therefore, the value of the total power, Ptot, in the system was determined and fixed at that concentration because energy cannot be created, by condition (a) above.
Also, for the same reason, the temperature cannot rise.
But, both can fall by losing energy to space. This is not destroying energy.
Now, suppose more carbon dioxide is emitted into the atmosphere. Of course, this is not energy, of itself, but more absorption will certainly occur, (assuming that there is still energy left to be absorbed). It cannot be prevented. So, Pgh increases.
Any effect on the surface temperature can only happen because of the feedback of Pgh to the surface. There is no other mechanism.
But, Pin is unchanged, and so Pout is unchanged, by condition (b) above.
From equation (1) therefore, it is clear that Psurf must decrease for any increase in CO2 above the immediate pre-anthropogenic concentration, and so the surface temperature must also decrease.
This is global COOLING.
It should be pointed out that the cooling involves the LOSS of energy to space. This is not destroying energy, and so Conservation is not contravened.
Measured increase in global temperature
It is generally accepted that surface temperatures have increased by about 1 degC since the start of anthropogenic activities. The correlation with increases in atmospheric carbon dioxide concentration initiated the development of the Greenhouse Gas theory for Global Warming. This is shown above to be incorrect.
However, the temperature rise is real, and so another explanation is required. It might be a reasonable idea to look, with caution, for another correlation.
A E Banner MInstP
Greenhouse Gas Effect causes Surface Cooling