Real-world climatic significance of ’the enhanced greenhouse effect’ – a straightforward test toward potential falsification.
A surface with a temperature above 0 K would have an incoming and an outgoing heat flux – it would gain its heat from somewhere (incoming heat flux) and at the same time give off heat to its surroundings according to its thermodynamic state. This outgoing heat flux would be the heat loss
of that surface.
The surface of the Earth is such a surface:
If the surface maintains thermodynamic equilibrium with its surroundings, the outgoing heat flux would balance the incoming exactly. And its temperature would remain constant.
To change the temperature of this surface, one thus has to do (at least) one of two things:
• Increase the incoming heat flux – the heat gain, or
• reduce the outgoing heat flux – the heat loss.
So, turning to Earth’s surface, a ’body’ holding a mean temperature of +15°C or 288K, and assuming it’s in a state of thermodynamic equilibrium (this will of course never really be the case 100%), this means the surface temperature remains constant and the heat flux OUT equals the heat flux IN (from the Sun) – according to the new Stephens et al. 2012 study, ~165 W/m2.
The total mean heat loss flux from the global surface of our planet is acquired by summing the shares from latent heat transfer (through evaporation), sensible heat transfer (through conduction/convection) and net thermal radiation (net IR UP).
What, then, can we do to raise the surface temperature from this state of equilibrium?
As already mentioned, there are two ways and two ways only:1)
We can increase the incoming heat (the heat gain), or2)
we can reduce the outgoing heat (the heat loss).
These two are distinctly different methods by which to accomplish surface warming.
the surface is warmed directly – by increasing a heat flux (the incoming one). Extra heat is supplied.
the surface is warmed INdirectly – by reducing a heat flux (the outgoing one). No extra heat is supplied.
(In both cases the opposite flux is assumed to remain constant.
This distinction is crucial.
The two distinct ways to achieve surface warming can be called:1)
The Solar Method, and2)
The Atmospheric Method.
Simply because of what the 2nd law of thermodynamics dictates. It says that heat (the net energy flow) between two warm objects in thermal contact will always go from the warmer to the cooler object, because a system like this will always spontaneously move toward the highest possible state of entropy, which in this case would be thermodynamic equilibrium (even temperature). In nature this process is irreversible.This process
described: ”When two systems come into thermal contact, they exchange energy through the microscopic interactions of their particles. When the systems are at different temperatures, the result is a spontaneous net flow of energy from higher to lower temperature, so that the higher temperature decreases [through heat loss] and the lower increases [through heat gain].”
The Sun is warmer than the Earth’s surface. Thus it CAN transfer heat to the surface. And it does. The NET FLOW OF ENERGY between the Sun and the Earth’s surface will spontaneously go from the former to the latter. Always.
The atmosphere, on the other hand, is cooler than the Earth’s surface. It can NOT transfer heat to the surface. And it doesn’t. It will of course always and continuously transfer thermal ENERGY to the surface, simply because it has a temperature above 0 K. But it can never, on a global scale, transfer HEAT. The NET FLOW OF ENERGY between the atmosphere and the Earth’s surface will spontaneously go from the latter to the former. Always.
As one can see, there are two strictly separate thermodynamic mechanisms at hand to explain surface warming.
And hence we have a way to determine how the observed global warming of the recent three and a half decades came about.
Through which of these two mechanisms was the global surface temperature raised?
This is important:
- The Sun can ONLY change (raise/lower) the surface temperature directly, that is
by changing the net energy INput – heat gain.
- The atmosphere can ONLY change the surface temperature INdirectly, that is by
changing the net energy OUTput – heat loss.
So, who is the culprit? The Sun or the Atmosphere?
We have two possible scenarios:a)
If the solar input increases, the Earth’s surface will warm directly. That means the surface temperature will rise first. And THEN, as a response, the total heat loss from the surface will start increasing. To catch up. It will potentially increase until the heat gap is closed (heat IN + <--> heat OUT) and balance is restored.b)
If the atmospheric forcing is strenghtened, for instance by increasing the optical depth to surface IR radiation through a rising atmospheric content of GHGs, the Earth’s surface will warm INdirectly. That means the total surface heat loss will be suppressed (reduced) first. And THEN, as a response, the surface temperature will start rising. And it will potentially rise until the heat gap is closed (heat IN <--> heat OUT –) and balance is restored.
You see the opposite course of events here?
The size of the heat gap and the time it takes to close it in each case will depend on the size and the rate of the change – how large is the change/divergence accomplished over how much time?
If the change is sudden and large, the closing process will take time. The imbalance will sustain for a considerable period.
If the change is small and gradual/incremental, the imbalance will hardly be observable, because the response mechanisms will have no problem keeping up with the continuous effort to open up the heat gap.
(From ’Earth's Climate Past and Future’ (W.F. Ruddiman, 2000).
Anyway, at this point I think you understand what we need to look for to determine where the observed global warming came from.
Returning to points a)
With direct surface heating (the Sun) the situation looks like this – heat IN + <--> heat OUT
. Then the total surface heat loss will have to increase FROM its original level to be able to balance the increased input.
With INdirect surface heating (the atmosphere) the situation looks like this – heat IN <--> heat OUT –
. Then the total surface heat loss will have to increase back up TO its original level to be able to mend the reduced output.
(In both cases, the surface temperature will rise in the meantime.
This leads us to the following realization:
The total heat loss (the heat/net energy flux OUT) from the Earth’s surface during observed warming can, if:The Sun is responsible for the warming
be observed to either remain constant/unchanged (if the increased forcing is very small and gradual) or to INCREASE
And if:The atmosphere is responsible for the warming
, the total global surface heat loss can ONLY
be observed to either remain constant/unchanged (if the increased forcing is very small and gradual) or to DECREASE
Conversely, in the solar case, the total heat loss can NOT be observed to DECREASE during warming.
And, in the atmospheric case, the total heat loss can NOT be observed to INCREASE during warming.So there you have it. The test.Has the total global heat loss from the Earth’s surface (latent heat transfer + sensible heat transfer + net IR) increased or decreased during the global warming period we’ve seen since the mid 70s?
Is the Sun or the atmosphere responsible?
Did the warming start at the surface or in the atmosphere?