The Ignoring Of Adiabatic Processes – Big Mistake
An attempt is made to reconcile the diabatic and adiabatic processes within a planetary atmosphere and in doing so show how changes in the radiative characeristics of constituent molecules in an atmosphere might not have an effect on the equilibrium temperature of the atmosphere and of the surface beneath it.
Applying the proposed scenario would appear to indicate why and how planetary atmospheres adjust themselves to the ideal lapse rate set by gravity despite divergences from that ideal lapse rate within the vertical temperature profile of the atmosphere.
Essentially, the adiabatic and diabatic loops must always match each other on any given planet at equilibrium because they are then of equal size and run at equal speed but are of opposite sign.
If any forcing element acts on the speed of either loop alone then the other loop changes its own speed to restore equilibrium.
Equilibrium temperature can only change when a forcing element acts on both loops together so as to change the amount of energy tied up in both loops by the same amount.
Only gravity, mass and insolation can achieve that.
1) Basic definitions.
Current climate science concentrates on the exchange of radiation between the Earth and Space and between the surface of the Earth and the top of the atmosphere (TOA).
However, the exchange of energy between the surface and TOA is an adiabatic mechanical process. The exchange of energy between surface and Space is a diabatic process involving the exchange of radiation.
Thus the two types of energy exchange are governed by different rules and it is the failure to realise how the two sets of rules interact within a planetary atmosphere that has caused climate science to get bogged down in a conceptual impasse.
I have encountered much confusion about the relevance of so called diabatic and adiabatic processes in the minds of both alarmed proponents of Anthropogenic Global Warming (AGW) and in the minds of many sceptics.
Here is a simplified summary of the nature of, and differences, between diabatic and adiabatic processes.
“Air that rises will cool adiabatically. Air that sinks will warm adiabatically. Diabatic temperature changes on the other hand can occur in the form of diabatic heating or diabatic cooling. The prime contributor to diabatic heating is the sun.”
Essentially, an adiabatic process is one where temperature changes can occur without addition or removal of energy and a diabatic process is one where temperature changes can only occur as a result of the addition and or removal of energy.
In light of that information we can divide the Earth’s energy budget into two distinct components as follows:
i) A diabatic effect whereby solar energy arriving at TOA penetrates into and through the atmosphere, increases the temperature of the surface and of air within the atmosphere and then leaves again. Energy is being added with a warming outcome but at thermal equilibrium energy out is equal to energy in. I call this the Solar Diabatic Loop (SDL)
ii) An adiabatic effect whereby air warmed by solar input then starts to rise, detaching itself from the surface, rising, expanding and cooling from adiabatic decompression then falling back towards the surface again until it regains contact with the surface having contracted and been warmed again by adiabatic compression. No energy is added or removed from the point at which the parcel of air detaches itself from the surface to the point where it regains contact with the surface yet the temperature changes both on the way up and on the way down. I call this the Atmospheric Adiabatic Loop (AAL).
2) System description
With regard to the diabatic process the exchange of radiation in and out reaches thermal equilibrium relatively quickly (leaving Earth’s oceans out of the scenario for current purposes) and once the temperature rise within the atmosphere has occurred then equilibrium has been achieved and energy in at TOA will match energy out.
With regard to the adiabatic process the exchange of energy does not simply involve radiation and so the process takes more time to reach equilibrium.
When an air parcel detaches itself from the surface during the process of rising it immediately begins to expand due to the reducing of the weight of atmosphere pressing down on it. As it expands, more and more of the kinetic energy (heat content or KE) is converted to potential energy (PE) which is not recorded on temperature sensors.
Whilst that KE is in the form of PE it does not form part of the exchange of radiation between Sun, Earth and Space. It remains locked within the atmosphere.
Throughout the rising process, heat in the form of KE is progressively being removed from the exchange of radiation and throughout the subsequent falling process heat in the form of KE is progressively being added back to the exchange of radiation.
At any specific moment a certain quantity of heat in the atmosphere is out of sensor range in the form of PE.
Note that the AAL is a closed circuit with no net effect because the KE to PE conversion on the rising side is exactly the same as the PE to KE conversion on the falling side. Conservation of energy is therefore preserved.
The adiabatic process, being mechanical rather than radiative, takes longer than the diabatic process.
The more the time that is taken by the adiabatic process the higher the temperature that the surface and atmosphere can reach without upsetting the equilibrium of the diabatic radiation exchange at TOA.
As long as the AAL is a closed loop and kept independent of the Solar Diabatic Loop (SDL) then system equilibrium is maintained however high the surface temperature might rise.
The energy being constantly recycled through the adiabatic loop was originally transferred from SDL to AAL at the time the gas molecules in the atmosphere first floated off the surface.
The amount of that energy was determined as follows:
i) The mass of the atmosphere – providing resistance to the flow of radiation through the atmosphere
ii) The level of solar input which determines the height by which molecules can rise from the surface. The more input the more kinetic energy the molecules will acquire and the higher they can rise.
ii) The intensity of the gravitational field which determines the speed at which the molecules can fall back to the surface.
3) System Change.
It is accepted science that one can change the equilibrium temperature of the system by changing atmospheric mass, the strength of the gravitational field or the power of solar input because each of those changes would affect the total amount of energy that the system could hold and so energy would be transferred between the AAL and the SDL in order to re balance the system and the inevitable outcome would be a change in equilibrium temperature for the system as a whole.
The current impasse in climate science has arisen because AGW proponents say that simply altering the radiative characteristics of constituent molecules within the atmosphere can result in a change in system equilibrium temperature without any need for an increase in mass, gravity or insolation.
I am not aware of that ever having been demonstrated so here I will try to work out whether that could happen.
i) The total exchange of radiation between Space and the TOA and between surface and the TOA is sufficiently large that an increase in the radiative capabilities of an atmospheric constituent that amounts to 0.04% of the atmosphere would appear unlikely to have any significant effect.
ii) The real question is whether changes in radiative characteristics alone can result in energy being transferred from the radiative SDL to the mechanical AAL so as to add to the energy in that latterLoop and thereby significantly increase the temperature of atmosphere and surface by in turn increasing the time delay in the transmission of energy through the system.
iii) There is little doubt that mass, gravity and insolation can do it but what about mere radiative characteristics?
iv) The answer must depend on whether any slowing down of the throughput of radiation from a mere change in radiative characteristics within the SDL would overwhelm the flexibility of the adiabatic processes in the AAL. If it could, then energy would transfer from SDL to AAL and equilibrium temperature must rise. If it cannot, then the speed of the AAL would change but not the amount of energy contained in it at any given moment and equilibrium temperature would not then need to rise.
4) The Atmospheric Adiabatic Loop (AAL)
We are all familiar with the AAL on a daily basis since it gives us weather and climate zones.
We also know how variable can be the speed of convective uplift in depressions and how rising air is related to low surface pressure and descending air to high pressure.
The adiabatic process within the AAL involves conversion of KE to PE and back again and at any given moment the surface has KE of 100% with PE at 0% and top of atmosphere PE nearly 100% and KE nearly 0%. I say ‘nearly’ at TOA because the temperature of Space is not quite at absolute zero so in practice there will still be a little KE even up there.
At some point in the vertical atmospheric column KE will equal PE and that is the point of equilibrium for the AAL.
That point can rise or fall depending on how fast the AAL is transferring energy up or down at any given moment.
If it runs faster for any reason the point of equilibrium will rise and if it runs slower for any reason then the point of equilibrium will fall.
There is, therefore, considerable flexibility in the speed at which it can operate and unless KE and PE become unbalanced throughout the entire vertical column then no energy can be transferred between the AAL and the SDL. There would need to be no point in the vertical column where KE = PE before energy could be transferred in or out of the AAL.
In order to unbalance KE and PE through the entire vertical column of the AAL requires that there be more total energy available to the system but established science says that can only occur from more mass, gravity or insolation.
One must increase the energy content of BOTH the AAL and SDL in order to raise equilibrium temperature. Changing the energy content of just one of the two loops will not be sufficient because the other loop will just change its own speed as an equal and opposite reaction.
This is what would happen:
Kinetic Energy (KE) + Potential Energy (PE) = constant at equilibrium for any given planet.
The value of the constant is only affected by mass, gravity and insolation.
Increasing the proportion of GHGs without increasing mass only affects the value of PE relative to KE with no change in the constant.
Let’s assume for the moment that more GHGs have a net warming effect.
More GHGs would increase PE relative to KE by causing the atmosphere to expand.
Less GHGs would decrease PE relative to KE by allowing the atmosphere to contract
If the constant does not change then the equilibrium temperature does not
(i) If one increases GHGs to slow down energy flow through the diabatic loop thereby warming that loop there will be an increase in PE relative to KE within the adiabatic loop instead of a change in the constant.
Since there has been no change in the constant the extra PE is created at the expense of KE and the adiabatic loop cools.
(ii) If one decreases GHGs to speed up the energy flow through the diabatic loop thereby cooling that loop there will be a reduction in PE relative to KE within the adiabatic loop instead of a change in the constant.
Since there has been no change in the constant the increase of KE relative to PE results in warming of the adiabatic loop.
If the net effect of more GHGs is actually system cooling then the reverse scenario would apply, still with no change in equilibrium temperature.
Thus the effect of changing the proportion of GHGs in the diabatic loop is to produce an equal and opposite thermal effect in the adiabatic loop which leaves equilibrium temperature constant.
Which is why ignoring the adiabatic processes is a big mistake.
Summary and conclusion:
Anything that causes faster radiation out produces a slower running AAL and anything that causes slower radiation out produces a faster running AAL unless mass, gravity and insolation also change at the same time.
A change in radiative characteristics alone does not make more energy available because solar insolation at TOA remains the same, mass stays the same and gravity stays the same.
Instead of transferring more energy from SDL to AAL the effect of changes in the proportion of radiatively active gases would simply be to adjust the speed of the AAL by changing the height within the vertical column at which KE = PE.
So, on those grounds, more GHGs could not affect equilibrium temperature because they provoke an equal and opposite system response to any effect they might have on the transfer of energy through the planetary system.
That is why established science does not list the radiative features of constituent gases as one of the factors that influence the equilibrium temperature of planets with atmospheres.
The similarity between Venus and Earth whereby they are each at much the same temperature at the same pressure subject only to an adjustment for distance from the sun despite vast differences in atmospheric composition is empirical proof.Published by Stephen Wilde December 15, 2012